LinuxTV Patchwork [1/7] media: aspeed: fix a kernel warning on clk control

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Submitter Jae Hyun Yoo
Date May 2, 2019, 7:13 p.m.
Message ID <20190502191317.29698-2-jae.hyun.yoo@linux.intel.com>
Download mbox | patch
Permalink /patch/55984/
State New
Delegated to: Hans Verkuil
Headers show

Comments

Jae Hyun Yoo - May 2, 2019, 7:13 p.m.
Video engine clock control functions in the Aspeed video engine
driver are being called from multiple context without any
protection so video clocks can be double disabled and eventually
it causes a kernel warning with stack dump printing out like below:

[  515.540498] ------------[ cut here ]------------
[  515.545174] WARNING: CPU: 0 PID: 1310 at drivers/clk/clk.c:684 clk_core_unprepare+0x13c/0x170
[  515.553806] vclk-gate already unprepared
[  515.557841] CPU: 0 PID: 1310 Comm: obmc-ikvm Tainted: G        W         5.0.6-df66fbc97853fbba90a0bfa44de32f3d5f7602b4 #1
[  515.568973] Hardware name: Generic DT based system
[  515.573777] Backtrace:
[  515.576272] [<80107cdc>] (dump_backtrace) from [<80107f10>] (show_stack+0x20/0x24)
[  515.583930]  r7:803a5614 r6:00000009 r5:00000000 r4:9d88fe1c
[  515.589712] [<80107ef0>] (show_stack) from [<80690184>] (dump_stack+0x20/0x28)
[  515.597053] [<80690164>] (dump_stack) from [<80116044>] (__warn.part.3+0xb4/0xdc)
[  515.604557] [<80115f90>] (__warn.part.3) from [<801160d8>] (warn_slowpath_fmt+0x6c/0x90)
[  515.612734]  r6:000002ac r5:8080befc r4:80a07008
[  515.617463] [<80116070>] (warn_slowpath_fmt) from [<803a5614>] (clk_core_unprepare+0x13c/0x170)
[  515.626167]  r3:8080cdf4 r2:8080bfc0
[  515.629834]  r7:98d682a8 r6:9d8a9200 r5:9e5151a0 r4:97abd620
[  515.635530] [<803a54d8>] (clk_core_unprepare) from [<803a76a4>] (clk_unprepare+0x34/0x3c)
[  515.643812]  r5:9e5151a0 r4:97abd620
[  515.647529] [<803a7670>] (clk_unprepare) from [<804f36ec>] (aspeed_video_off+0x38/0x50)
[  515.655539]  r5:9e5151a0 r4:9e504000
[  515.659242] [<804f36b4>] (aspeed_video_off) from [<804f4358>] (aspeed_video_release+0x90/0x114)
[  515.668036]  r5:9e5044b0 r4:9e504000
[  515.671643] [<804f42c8>] (aspeed_video_release) from [<804d302c>] (v4l2_release+0xd4/0xe8)
[  515.679999]  r7:98d682a8 r6:9d087810 r5:9d8a9200 r4:9e504318
[  515.685695] [<804d2f58>] (v4l2_release) from [<80236454>] (__fput+0x98/0x1c4)
[  515.692914]  r5:9e51b608 r4:9d8a9200
[  515.696597] [<802363bc>] (__fput) from [<802365e8>] (____fput+0x18/0x1c)
[  515.703315]  r9:80a0700c r8:801011e4 r7:00000000 r6:80a64b9c r5:9d8e35a0 r4:9d8e38dc
[  515.711167] [<802365d0>] (____fput) from [<80131ca4>] (task_work_run+0x7c/0xa0)
[  515.718596] [<80131c28>] (task_work_run) from [<80106884>] (do_work_pending+0x4a8/0x578)
[  515.726777]  r7:801011e4 r6:80a07008 r5:9d88ffb0 r4:ffffe000
[  515.732466] [<801063dc>] (do_work_pending) from [<8010106c>] (slow_work_pending+0xc/0x20)
[  515.740727] Exception stack(0x9d88ffb0 to 0x9d88fff8)
[  515.745840] ffa0:                                     00000000 76f18094 00000000 00000000
[  515.754122] ffc0: 00000007 00176778 7eda4c20 00000006 00000000 00000000 48e20fa4 00000000
[  515.762386] ffe0: 00000002 7eda4b08 00000000 48f91efc 80000010 00000007
[  515.769097]  r10:00000000 r9:9d88e000 r8:801011e4 r7:00000006 r6:7eda4c20 r5:00176778
[  515.777006]  r4:00000007
[  515.779558] ---[ end trace 12c04aadef8afbbb ]---
[  515.784176] ------------[ cut here ]------------
[  515.788817] WARNING: CPU: 0 PID: 1310 at drivers/clk/clk.c:825 clk_core_disable+0x18c/0x204
[  515.797161] eclk-gate already disabled
[  515.800916] CPU: 0 PID: 1310 Comm: obmc-ikvm Tainted: G        W         5.0.6-df66fbc97853fbba90a0bfa44de32f3d5f7602b4 #1
[  515.811945] Hardware name: Generic DT based system
[  515.816730] Backtrace:
[  515.819210] [<80107cdc>] (dump_backtrace) from [<80107f10>] (show_stack+0x20/0x24)
[  515.826782]  r7:803a5900 r6:00000009 r5:00000000 r4:9d88fe04
[  515.832454] [<80107ef0>] (show_stack) from [<80690184>] (dump_stack+0x20/0x28)
[  515.839687] [<80690164>] (dump_stack) from [<80116044>] (__warn.part.3+0xb4/0xdc)
[  515.847170] [<80115f90>] (__warn.part.3) from [<801160d8>] (warn_slowpath_fmt+0x6c/0x90)
[  515.855247]  r6:00000339 r5:8080befc r4:80a07008
[  515.859868] [<80116070>] (warn_slowpath_fmt) from [<803a5900>] (clk_core_disable+0x18c/0x204)
[  515.868385]  r3:8080cdd0 r2:8080c00c
[  515.871957]  r7:98d682a8 r6:9d8a9200 r5:97abd560 r4:97abd560
[  515.877615] [<803a5774>] (clk_core_disable) from [<803a59a0>] (clk_core_disable_lock+0x28/0x34)
[  515.886301]  r7:98d682a8 r6:9d8a9200 r5:97abd560 r4:a0000013
[  515.891960] [<803a5978>] (clk_core_disable_lock) from [<803a7714>] (clk_disable+0x2c/0x30)
[  515.900216]  r5:9e5151a0 r4:9e515f60
[  515.903816] [<803a76e8>] (clk_disable) from [<804f36f8>] (aspeed_video_off+0x44/0x50)
[  515.911656] [<804f36b4>] (aspeed_video_off) from [<804f4358>] (aspeed_video_release+0x90/0x114)
[  515.920341]  r5:9e5044b0 r4:9e504000
[  515.923921] [<804f42c8>] (aspeed_video_release) from [<804d302c>] (v4l2_release+0xd4/0xe8)
[  515.932184]  r7:98d682a8 r6:9d087810 r5:9d8a9200 r4:9e504318
[  515.937851] [<804d2f58>] (v4l2_release) from [<80236454>] (__fput+0x98/0x1c4)
[  515.944980]  r5:9e51b608 r4:9d8a9200
[  515.948559] [<802363bc>] (__fput) from [<802365e8>] (____fput+0x18/0x1c)
[  515.955257]  r9:80a0700c r8:801011e4 r7:00000000 r6:80a64b9c r5:9d8e35a0 r4:9d8e38dc
[  515.963008] [<802365d0>] (____fput) from [<80131ca4>] (task_work_run+0x7c/0xa0)
[  515.970333] [<80131c28>] (task_work_run) from [<80106884>] (do_work_pending+0x4a8/0x578)
[  515.978421]  r7:801011e4 r6:80a07008 r5:9d88ffb0 r4:ffffe000
[  515.984086] [<801063dc>] (do_work_pending) from [<8010106c>] (slow_work_pending+0xc/0x20)
[  515.992247] Exception stack(0x9d88ffb0 to 0x9d88fff8)
[  515.997296] ffa0:                                     00000000 76f18094 00000000 00000000
[  516.005473] ffc0: 00000007 00176778 7eda4c20 00000006 00000000 00000000 48e20fa4 00000000
[  516.013642] ffe0: 00000002 7eda4b08 00000000 48f91efc 80000010 00000007
[  516.020257]  r10:00000000 r9:9d88e000 r8:801011e4 r7:00000006 r6:7eda4c20 r5:00176778
[  516.028072]  r4:00000007
[  516.030606] ---[ end trace 12c04aadef8afbbc ]---

To prevent this issue, this commit adds spinlock protection and
clock status checking logic into the Aspeed video engine driver.

Signed-off-by: Jae Hyun Yoo <jae.hyun.yoo@linux.intel.com>
Reviewed-by: Eddie James <eajames@linux.ibm.com>
---
 drivers/media/platform/aspeed-video.c | 32 ++++++++++++++++++++++++---
 1 file changed, 29 insertions(+), 3 deletions(-)
Benjamin Herrenschmidt - May 8, 2019, 6:31 a.m.
On Thu, 2019-05-02 at 12:13 -0700, Jae Hyun Yoo wrote:
> Video engine clock control functions in the Aspeed video engine
> driver are being called from multiple context without any
> protection so video clocks can be double disabled and eventually
> it causes a kernel warning with stack dump printing out like below:

I already objected to the use of set_bit, clear_bit etc...

Either you are protected by a spinlock, in which case you don't need
them, use either the __ versions (non atomic) or just a bloody bool
flag which is a lot clearer and will generated better code. Or you
aren't protected in which case the code seems racy.


> [  515.540498] ------------[ cut here ]------------
> [  515.545174] WARNING: CPU: 0 PID: 1310 at drivers/clk/clk.c:684
> clk_core_unprepare+0x13c/0x170
> [  515.553806] vclk-gate already unprepared
> [  515.557841] CPU: 0 PID: 1310 Comm: obmc-ikvm Tainted:
> G        W         5.0.6-df66fbc97853fbba90a0bfa44de32f3d5f7602b4 #1
> [  515.568973] Hardware name: Generic DT based system
> [  515.573777] Backtrace:
> [  515.576272] [<80107cdc>] (dump_backtrace) from [<80107f10>]
> (show_stack+0x20/0x24)
> [  515.583930]  r7:803a5614 r6:00000009 r5:00000000 r4:9d88fe1c
> [  515.589712] [<80107ef0>] (show_stack) from [<80690184>]
> (dump_stack+0x20/0x28)
> [  515.597053] [<80690164>] (dump_stack) from [<80116044>]
> (__warn.part.3+0xb4/0xdc)
> [  515.604557] [<80115f90>] (__warn.part.3) from [<801160d8>]
> (warn_slowpath_fmt+0x6c/0x90)
> [  515.612734]  r6:000002ac r5:8080befc r4:80a07008
> [  515.617463] [<80116070>] (warn_slowpath_fmt) from [<803a5614>]
> (clk_core_unprepare+0x13c/0x170)
> [  515.626167]  r3:8080cdf4 r2:8080bfc0
> [  515.629834]  r7:98d682a8 r6:9d8a9200 r5:9e5151a0 r4:97abd620
> [  515.635530] [<803a54d8>] (clk_core_unprepare) from [<803a76a4>]
> (clk_unprepare+0x34/0x3c)
> [  515.643812]  r5:9e5151a0 r4:97abd620
> [  515.647529] [<803a7670>] (clk_unprepare) from [<804f36ec>]
> (aspeed_video_off+0x38/0x50)
> [  515.655539]  r5:9e5151a0 r4:9e504000
> [  515.659242] [<804f36b4>] (aspeed_video_off) from [<804f4358>]
> (aspeed_video_release+0x90/0x114)
> [  515.668036]  r5:9e5044b0 r4:9e504000
> [  515.671643] [<804f42c8>] (aspeed_video_release) from [<804d302c>]
> (v4l2_release+0xd4/0xe8)
> [  515.679999]  r7:98d682a8 r6:9d087810 r5:9d8a9200 r4:9e504318
> [  515.685695] [<804d2f58>] (v4l2_release) from [<80236454>]
> (__fput+0x98/0x1c4)
> [  515.692914]  r5:9e51b608 r4:9d8a9200
> [  515.696597] [<802363bc>] (__fput) from [<802365e8>]
> (____fput+0x18/0x1c)
> [  515.703315]  r9:80a0700c r8:801011e4 r7:00000000 r6:80a64b9c
> r5:9d8e35a0 r4:9d8e38dc
> [  515.711167] [<802365d0>] (____fput) from [<80131ca4>]
> (task_work_run+0x7c/0xa0)
> [  515.718596] [<80131c28>] (task_work_run) from [<80106884>]
> (do_work_pending+0x4a8/0x578)
> [  515.726777]  r7:801011e4 r6:80a07008 r5:9d88ffb0 r4:ffffe000
> [  515.732466] [<801063dc>] (do_work_pending) from [<8010106c>]
> (slow_work_pending+0xc/0x20)
> [  515.740727] Exception stack(0x9d88ffb0 to 0x9d88fff8)
> [  515.745840] ffa0:                                     00000000
> 76f18094 00000000 00000000
> [  515.754122] ffc0: 00000007 00176778 7eda4c20 00000006 00000000
> 00000000 48e20fa4 00000000
> [  515.762386] ffe0: 00000002 7eda4b08 00000000 48f91efc 80000010
> 00000007
> [  515.769097]  r10:00000000 r9:9d88e000 r8:801011e4 r7:00000006
> r6:7eda4c20 r5:00176778
> [  515.777006]  r4:00000007
> [  515.779558] ---[ end trace 12c04aadef8afbbb ]---
> [  515.784176] ------------[ cut here ]------------
> [  515.788817] WARNING: CPU: 0 PID: 1310 at drivers/clk/clk.c:825
> clk_core_disable+0x18c/0x204
> [  515.797161] eclk-gate already disabled
> [  515.800916] CPU: 0 PID: 1310 Comm: obmc-ikvm Tainted:
> G        W         5.0.6-df66fbc97853fbba90a0bfa44de32f3d5f7602b4 #1
> [  515.811945] Hardware name: Generic DT based system
> [  515.816730] Backtrace:
> [  515.819210] [<80107cdc>] (dump_backtrace) from [<80107f10>]
> (show_stack+0x20/0x24)
> [  515.826782]  r7:803a5900 r6:00000009 r5:00000000 r4:9d88fe04
> [  515.832454] [<80107ef0>] (show_stack) from [<80690184>]
> (dump_stack+0x20/0x28)
> [  515.839687] [<80690164>] (dump_stack) from [<80116044>]
> (__warn.part.3+0xb4/0xdc)
> [  515.847170] [<80115f90>] (__warn.part.3) from [<801160d8>]
> (warn_slowpath_fmt+0x6c/0x90)
> [  515.855247]  r6:00000339 r5:8080befc r4:80a07008
> [  515.859868] [<80116070>] (warn_slowpath_fmt) from [<803a5900>]
> (clk_core_disable+0x18c/0x204)
> [  515.868385]  r3:8080cdd0 r2:8080c00c
> [  515.871957]  r7:98d682a8 r6:9d8a9200 r5:97abd560 r4:97abd560
> [  515.877615] [<803a5774>] (clk_core_disable) from [<803a59a0>]
> (clk_core_disable_lock+0x28/0x34)
> [  515.886301]  r7:98d682a8 r6:9d8a9200 r5:97abd560 r4:a0000013
> [  515.891960] [<803a5978>] (clk_core_disable_lock) from [<803a7714>]
> (clk_disable+0x2c/0x30)
> [  515.900216]  r5:9e5151a0 r4:9e515f60
> [  515.903816] [<803a76e8>] (clk_disable) from [<804f36f8>]
> (aspeed_video_off+0x44/0x50)
> [  515.911656] [<804f36b4>] (aspeed_video_off) from [<804f4358>]
> (aspeed_video_release+0x90/0x114)
> [  515.920341]  r5:9e5044b0 r4:9e504000
> [  515.923921] [<804f42c8>] (aspeed_video_release) from [<804d302c>]
> (v4l2_release+0xd4/0xe8)
> [  515.932184]  r7:98d682a8 r6:9d087810 r5:9d8a9200 r4:9e504318
> [  515.937851] [<804d2f58>] (v4l2_release) from [<80236454>]
> (__fput+0x98/0x1c4)
> [  515.944980]  r5:9e51b608 r4:9d8a9200
> [  515.948559] [<802363bc>] (__fput) from [<802365e8>]
> (____fput+0x18/0x1c)
> [  515.955257]  r9:80a0700c r8:801011e4 r7:00000000 r6:80a64b9c
> r5:9d8e35a0 r4:9d8e38dc
> [  515.963008] [<802365d0>] (____fput) from [<80131ca4>]
> (task_work_run+0x7c/0xa0)
> [  515.970333] [<80131c28>] (task_work_run) from [<80106884>]
> (do_work_pending+0x4a8/0x578)
> [  515.978421]  r7:801011e4 r6:80a07008 r5:9d88ffb0 r4:ffffe000
> [  515.984086] [<801063dc>] (do_work_pending) from [<8010106c>]
> (slow_work_pending+0xc/0x20)
> [  515.992247] Exception stack(0x9d88ffb0 to 0x9d88fff8)
> [  515.997296] ffa0:                                     00000000
> 76f18094 00000000 00000000
> [  516.005473] ffc0: 00000007 00176778 7eda4c20 00000006 00000000
> 00000000 48e20fa4 00000000
> [  516.013642] ffe0: 00000002 7eda4b08 00000000 48f91efc 80000010
> 00000007
> [  516.020257]  r10:00000000 r9:9d88e000 r8:801011e4 r7:00000006
> r6:7eda4c20 r5:00176778
> [  516.028072]  r4:00000007
> [  516.030606] ---[ end trace 12c04aadef8afbbc ]---
> 
> To prevent this issue, this commit adds spinlock protection and
> clock status checking logic into the Aspeed video engine driver.
> 
> Signed-off-by: Jae Hyun Yoo <jae.hyun.yoo@linux.intel.com>
> Reviewed-by: Eddie James <eajames@linux.ibm.com>
> ---
>  drivers/media/platform/aspeed-video.c | 32 ++++++++++++++++++++++++-
> --
>  1 file changed, 29 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/media/platform/aspeed-video.c
> b/drivers/media/platform/aspeed-video.c
> index 55c55a68b016..2dac6d20b180 100644
> --- a/drivers/media/platform/aspeed-video.c
> +++ b/drivers/media/platform/aspeed-video.c
> @@ -187,6 +187,7 @@ enum {
>  	VIDEO_STREAMING,
>  	VIDEO_FRAME_INPRG,
>  	VIDEO_STOPPED,
> +	VIDEO_CLOCKS_ON,
>  };
>  
>  struct aspeed_video_addr {
> @@ -483,19 +484,29 @@ static void
> aspeed_video_enable_mode_detect(struct aspeed_video *video)
>  
>  static void aspeed_video_off(struct aspeed_video *video)
>  {
> +	if (!test_bit(VIDEO_CLOCKS_ON, &video->flags))
> +		return;
> +
>  	/* Disable interrupts */
>  	aspeed_video_write(video, VE_INTERRUPT_CTRL, 0);
>  
>  	/* Turn off the relevant clocks */
>  	clk_disable_unprepare(video->vclk);
>  	clk_disable_unprepare(video->eclk);
> +
> +	clear_bit(VIDEO_CLOCKS_ON, &video->flags);
>  }
>  
>  static void aspeed_video_on(struct aspeed_video *video)
>  {
> +	if (test_bit(VIDEO_CLOCKS_ON, &video->flags))
> +		return;
> +
>  	/* Turn on the relevant clocks */
>  	clk_prepare_enable(video->eclk);
>  	clk_prepare_enable(video->vclk);
> +
> +	set_bit(VIDEO_CLOCKS_ON, &video->flags);
>  }
>  
>  static void aspeed_video_bufs_done(struct aspeed_video *video,
> @@ -513,12 +524,14 @@ static void aspeed_video_bufs_done(struct
> aspeed_video *video,
>  
>  static void aspeed_video_irq_res_change(struct aspeed_video *video)
>  {
> +	spin_lock(&video->lock);
>  	dev_dbg(video->dev, "Resolution changed; resetting\n");
>  
>  	set_bit(VIDEO_RES_CHANGE, &video->flags);
>  	clear_bit(VIDEO_FRAME_INPRG, &video->flags);
>  
>  	aspeed_video_off(video);
> +	spin_unlock(&video->lock);
>  	aspeed_video_bufs_done(video, VB2_BUF_STATE_ERROR);
>  
>  	schedule_delayed_work(&video->res_work,
> RESOLUTION_CHANGE_DELAY);
> @@ -938,9 +951,13 @@ static void aspeed_video_init_regs(struct
> aspeed_video *video)
>  
>  static void aspeed_video_start(struct aspeed_video *video)
>  {
> +	unsigned long flags;
> +
> +	spin_lock_irqsave(&video->lock, flags);
>  	aspeed_video_on(video);
>  
>  	aspeed_video_init_regs(video);
> +	spin_unlock_irqrestore(&video->lock, flags);
>  
>  	/* Resolution set to 640x480 if no signal found */
>  	aspeed_video_get_resolution(video);
> @@ -956,6 +973,9 @@ static void aspeed_video_start(struct
> aspeed_video *video)
>  
>  static void aspeed_video_stop(struct aspeed_video *video)
>  {
> +	unsigned long flags;
> +
> +	spin_lock_irqsave(&video->lock, flags);
>  	set_bit(VIDEO_STOPPED, &video->flags);
>  	cancel_delayed_work_sync(&video->res_work);
>  
> @@ -969,6 +989,7 @@ static void aspeed_video_stop(struct aspeed_video
> *video)
>  
>  	video->v4l2_input_status = V4L2_IN_ST_NO_SIGNAL;
>  	video->flags = 0;
> +	spin_unlock_irqrestore(&video->lock, flags);
>  }
>  
>  static int aspeed_video_querycap(struct file *file, void *fh,
> @@ -1306,16 +1327,21 @@ static void
> aspeed_video_resolution_work(struct work_struct *work)
>  	struct delayed_work *dwork = to_delayed_work(work);
>  	struct aspeed_video *video = container_of(dwork, struct
> aspeed_video,
>  						  res_work);
> -	u32 input_status = video->v4l2_input_status;
> +	unsigned long flags;
> +	u32 input_status;
>  
> +	spin_lock_irqsave(&video->lock, flags);
> +	input_status = video->v4l2_input_status;
>  	aspeed_video_on(video);
>  
>  	/* Exit early in case no clients remain */
> -	if (test_bit(VIDEO_STOPPED, &video->flags))
> +	if (test_bit(VIDEO_STOPPED, &video->flags)) {
> +		spin_unlock_irqrestore(&video->lock, flags);
>  		goto done;
> +	}
>  
>  	aspeed_video_init_regs(video);
> -
> +	spin_unlock_irqrestore(&video->lock, flags);
>  	aspeed_video_get_resolution(video);
>  
>  	if (video->detected_timings.width != video-
> >active_timings.width ||
Jae Hyun Yoo - May 8, 2019, 10:19 p.m.
On 5/7/2019 11:31 PM, Benjamin Herrenschmidt wrote:
> On Thu, 2019-05-02 at 12:13 -0700, Jae Hyun Yoo wrote:
>> Video engine clock control functions in the Aspeed video engine
>> driver are being called from multiple context without any
>> protection so video clocks can be double disabled and eventually
>> it causes a kernel warning with stack dump printing out like below:
> 
> I already objected to the use of set_bit, clear_bit etc...
> 
> Either you are protected by a spinlock, in which case you don't need
> them, use either the __ versions (non atomic) or just a bloody bool
> flag which is a lot clearer and will generated better code. Or you
> aren't protected in which case the code seems racy.

Got it. I'll use __set_bit and __clear_bit instead. Thanks for
your pointing it out.

Regards,
Jae

>> [  515.540498] ------------[ cut here ]------------
>> [  515.545174] WARNING: CPU: 0 PID: 1310 at drivers/clk/clk.c:684
>> clk_core_unprepare+0x13c/0x170
>> [  515.553806] vclk-gate already unprepared
>> [  515.557841] CPU: 0 PID: 1310 Comm: obmc-ikvm Tainted:
>> G        W         5.0.6-df66fbc97853fbba90a0bfa44de32f3d5f7602b4 #1
>> [  515.568973] Hardware name: Generic DT based system
>> [  515.573777] Backtrace:
>> [  515.576272] [<80107cdc>] (dump_backtrace) from [<80107f10>]
>> (show_stack+0x20/0x24)
>> [  515.583930]  r7:803a5614 r6:00000009 r5:00000000 r4:9d88fe1c
>> [  515.589712] [<80107ef0>] (show_stack) from [<80690184>]
>> (dump_stack+0x20/0x28)
>> [  515.597053] [<80690164>] (dump_stack) from [<80116044>]
>> (__warn.part.3+0xb4/0xdc)
>> [  515.604557] [<80115f90>] (__warn.part.3) from [<801160d8>]
>> (warn_slowpath_fmt+0x6c/0x90)
>> [  515.612734]  r6:000002ac r5:8080befc r4:80a07008
>> [  515.617463] [<80116070>] (warn_slowpath_fmt) from [<803a5614>]
>> (clk_core_unprepare+0x13c/0x170)
>> [  515.626167]  r3:8080cdf4 r2:8080bfc0
>> [  515.629834]  r7:98d682a8 r6:9d8a9200 r5:9e5151a0 r4:97abd620
>> [  515.635530] [<803a54d8>] (clk_core_unprepare) from [<803a76a4>]
>> (clk_unprepare+0x34/0x3c)
>> [  515.643812]  r5:9e5151a0 r4:97abd620
>> [  515.647529] [<803a7670>] (clk_unprepare) from [<804f36ec>]
>> (aspeed_video_off+0x38/0x50)
>> [  515.655539]  r5:9e5151a0 r4:9e504000
>> [  515.659242] [<804f36b4>] (aspeed_video_off) from [<804f4358>]
>> (aspeed_video_release+0x90/0x114)
>> [  515.668036]  r5:9e5044b0 r4:9e504000
>> [  515.671643] [<804f42c8>] (aspeed_video_release) from [<804d302c>]
>> (v4l2_release+0xd4/0xe8)
>> [  515.679999]  r7:98d682a8 r6:9d087810 r5:9d8a9200 r4:9e504318
>> [  515.685695] [<804d2f58>] (v4l2_release) from [<80236454>]
>> (__fput+0x98/0x1c4)
>> [  515.692914]  r5:9e51b608 r4:9d8a9200
>> [  515.696597] [<802363bc>] (__fput) from [<802365e8>]
>> (____fput+0x18/0x1c)
>> [  515.703315]  r9:80a0700c r8:801011e4 r7:00000000 r6:80a64b9c
>> r5:9d8e35a0 r4:9d8e38dc
>> [  515.711167] [<802365d0>] (____fput) from [<80131ca4>]
>> (task_work_run+0x7c/0xa0)
>> [  515.718596] [<80131c28>] (task_work_run) from [<80106884>]
>> (do_work_pending+0x4a8/0x578)
>> [  515.726777]  r7:801011e4 r6:80a07008 r5:9d88ffb0 r4:ffffe000
>> [  515.732466] [<801063dc>] (do_work_pending) from [<8010106c>]
>> (slow_work_pending+0xc/0x20)
>> [  515.740727] Exception stack(0x9d88ffb0 to 0x9d88fff8)
>> [  515.745840] ffa0:                                     00000000
>> 76f18094 00000000 00000000
>> [  515.754122] ffc0: 00000007 00176778 7eda4c20 00000006 00000000
>> 00000000 48e20fa4 00000000
>> [  515.762386] ffe0: 00000002 7eda4b08 00000000 48f91efc 80000010
>> 00000007
>> [  515.769097]  r10:00000000 r9:9d88e000 r8:801011e4 r7:00000006
>> r6:7eda4c20 r5:00176778
>> [  515.777006]  r4:00000007
>> [  515.779558] ---[ end trace 12c04aadef8afbbb ]---
>> [  515.784176] ------------[ cut here ]------------
>> [  515.788817] WARNING: CPU: 0 PID: 1310 at drivers/clk/clk.c:825
>> clk_core_disable+0x18c/0x204
>> [  515.797161] eclk-gate already disabled
>> [  515.800916] CPU: 0 PID: 1310 Comm: obmc-ikvm Tainted:
>> G        W         5.0.6-df66fbc97853fbba90a0bfa44de32f3d5f7602b4 #1
>> [  515.811945] Hardware name: Generic DT based system
>> [  515.816730] Backtrace:
>> [  515.819210] [<80107cdc>] (dump_backtrace) from [<80107f10>]
>> (show_stack+0x20/0x24)
>> [  515.826782]  r7:803a5900 r6:00000009 r5:00000000 r4:9d88fe04
>> [  515.832454] [<80107ef0>] (show_stack) from [<80690184>]
>> (dump_stack+0x20/0x28)
>> [  515.839687] [<80690164>] (dump_stack) from [<80116044>]
>> (__warn.part.3+0xb4/0xdc)
>> [  515.847170] [<80115f90>] (__warn.part.3) from [<801160d8>]
>> (warn_slowpath_fmt+0x6c/0x90)
>> [  515.855247]  r6:00000339 r5:8080befc r4:80a07008
>> [  515.859868] [<80116070>] (warn_slowpath_fmt) from [<803a5900>]
>> (clk_core_disable+0x18c/0x204)
>> [  515.868385]  r3:8080cdd0 r2:8080c00c
>> [  515.871957]  r7:98d682a8 r6:9d8a9200 r5:97abd560 r4:97abd560
>> [  515.877615] [<803a5774>] (clk_core_disable) from [<803a59a0>]
>> (clk_core_disable_lock+0x28/0x34)
>> [  515.886301]  r7:98d682a8 r6:9d8a9200 r5:97abd560 r4:a0000013
>> [  515.891960] [<803a5978>] (clk_core_disable_lock) from [<803a7714>]
>> (clk_disable+0x2c/0x30)
>> [  515.900216]  r5:9e5151a0 r4:9e515f60
>> [  515.903816] [<803a76e8>] (clk_disable) from [<804f36f8>]
>> (aspeed_video_off+0x44/0x50)
>> [  515.911656] [<804f36b4>] (aspeed_video_off) from [<804f4358>]
>> (aspeed_video_release+0x90/0x114)
>> [  515.920341]  r5:9e5044b0 r4:9e504000
>> [  515.923921] [<804f42c8>] (aspeed_video_release) from [<804d302c>]
>> (v4l2_release+0xd4/0xe8)
>> [  515.932184]  r7:98d682a8 r6:9d087810 r5:9d8a9200 r4:9e504318
>> [  515.937851] [<804d2f58>] (v4l2_release) from [<80236454>]
>> (__fput+0x98/0x1c4)
>> [  515.944980]  r5:9e51b608 r4:9d8a9200
>> [  515.948559] [<802363bc>] (__fput) from [<802365e8>]
>> (____fput+0x18/0x1c)
>> [  515.955257]  r9:80a0700c r8:801011e4 r7:00000000 r6:80a64b9c
>> r5:9d8e35a0 r4:9d8e38dc
>> [  515.963008] [<802365d0>] (____fput) from [<80131ca4>]
>> (task_work_run+0x7c/0xa0)
>> [  515.970333] [<80131c28>] (task_work_run) from [<80106884>]
>> (do_work_pending+0x4a8/0x578)
>> [  515.978421]  r7:801011e4 r6:80a07008 r5:9d88ffb0 r4:ffffe000
>> [  515.984086] [<801063dc>] (do_work_pending) from [<8010106c>]
>> (slow_work_pending+0xc/0x20)
>> [  515.992247] Exception stack(0x9d88ffb0 to 0x9d88fff8)
>> [  515.997296] ffa0:                                     00000000
>> 76f18094 00000000 00000000
>> [  516.005473] ffc0: 00000007 00176778 7eda4c20 00000006 00000000
>> 00000000 48e20fa4 00000000
>> [  516.013642] ffe0: 00000002 7eda4b08 00000000 48f91efc 80000010
>> 00000007
>> [  516.020257]  r10:00000000 r9:9d88e000 r8:801011e4 r7:00000006
>> r6:7eda4c20 r5:00176778
>> [  516.028072]  r4:00000007
>> [  516.030606] ---[ end trace 12c04aadef8afbbc ]---
>>
>> To prevent this issue, this commit adds spinlock protection and
>> clock status checking logic into the Aspeed video engine driver.
>>
>> Signed-off-by: Jae Hyun Yoo <jae.hyun.yoo@linux.intel.com>
>> Reviewed-by: Eddie James <eajames@linux.ibm.com>
>> ---
>>   drivers/media/platform/aspeed-video.c | 32 ++++++++++++++++++++++++-
>> --
>>   1 file changed, 29 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/media/platform/aspeed-video.c
>> b/drivers/media/platform/aspeed-video.c
>> index 55c55a68b016..2dac6d20b180 100644
>> --- a/drivers/media/platform/aspeed-video.c
>> +++ b/drivers/media/platform/aspeed-video.c
>> @@ -187,6 +187,7 @@ enum {
>>   	VIDEO_STREAMING,
>>   	VIDEO_FRAME_INPRG,
>>   	VIDEO_STOPPED,
>> +	VIDEO_CLOCKS_ON,
>>   };
>>   
>>   struct aspeed_video_addr {
>> @@ -483,19 +484,29 @@ static void
>> aspeed_video_enable_mode_detect(struct aspeed_video *video)
>>   
>>   static void aspeed_video_off(struct aspeed_video *video)
>>   {
>> +	if (!test_bit(VIDEO_CLOCKS_ON, &video->flags))
>> +		return;
>> +
>>   	/* Disable interrupts */
>>   	aspeed_video_write(video, VE_INTERRUPT_CTRL, 0);
>>   
>>   	/* Turn off the relevant clocks */
>>   	clk_disable_unprepare(video->vclk);
>>   	clk_disable_unprepare(video->eclk);
>> +
>> +	clear_bit(VIDEO_CLOCKS_ON, &video->flags);
>>   }
>>   
>>   static void aspeed_video_on(struct aspeed_video *video)
>>   {
>> +	if (test_bit(VIDEO_CLOCKS_ON, &video->flags))
>> +		return;
>> +
>>   	/* Turn on the relevant clocks */
>>   	clk_prepare_enable(video->eclk);
>>   	clk_prepare_enable(video->vclk);
>> +
>> +	set_bit(VIDEO_CLOCKS_ON, &video->flags);
>>   }
>>   
>>   static void aspeed_video_bufs_done(struct aspeed_video *video,
>> @@ -513,12 +524,14 @@ static void aspeed_video_bufs_done(struct
>> aspeed_video *video,
>>   
>>   static void aspeed_video_irq_res_change(struct aspeed_video *video)
>>   {
>> +	spin_lock(&video->lock);
>>   	dev_dbg(video->dev, "Resolution changed; resetting\n");
>>   
>>   	set_bit(VIDEO_RES_CHANGE, &video->flags);
>>   	clear_bit(VIDEO_FRAME_INPRG, &video->flags);
>>   
>>   	aspeed_video_off(video);
>> +	spin_unlock(&video->lock);
>>   	aspeed_video_bufs_done(video, VB2_BUF_STATE_ERROR);
>>   
>>   	schedule_delayed_work(&video->res_work,
>> RESOLUTION_CHANGE_DELAY);
>> @@ -938,9 +951,13 @@ static void aspeed_video_init_regs(struct
>> aspeed_video *video)
>>   
>>   static void aspeed_video_start(struct aspeed_video *video)
>>   {
>> +	unsigned long flags;
>> +
>> +	spin_lock_irqsave(&video->lock, flags);
>>   	aspeed_video_on(video);
>>   
>>   	aspeed_video_init_regs(video);
>> +	spin_unlock_irqrestore(&video->lock, flags);
>>   
>>   	/* Resolution set to 640x480 if no signal found */
>>   	aspeed_video_get_resolution(video);
>> @@ -956,6 +973,9 @@ static void aspeed_video_start(struct
>> aspeed_video *video)
>>   
>>   static void aspeed_video_stop(struct aspeed_video *video)
>>   {
>> +	unsigned long flags;
>> +
>> +	spin_lock_irqsave(&video->lock, flags);
>>   	set_bit(VIDEO_STOPPED, &video->flags);
>>   	cancel_delayed_work_sync(&video->res_work);
>>   
>> @@ -969,6 +989,7 @@ static void aspeed_video_stop(struct aspeed_video
>> *video)
>>   
>>   	video->v4l2_input_status = V4L2_IN_ST_NO_SIGNAL;
>>   	video->flags = 0;
>> +	spin_unlock_irqrestore(&video->lock, flags);
>>   }
>>   
>>   static int aspeed_video_querycap(struct file *file, void *fh,
>> @@ -1306,16 +1327,21 @@ static void
>> aspeed_video_resolution_work(struct work_struct *work)
>>   	struct delayed_work *dwork = to_delayed_work(work);
>>   	struct aspeed_video *video = container_of(dwork, struct
>> aspeed_video,
>>   						  res_work);
>> -	u32 input_status = video->v4l2_input_status;
>> +	unsigned long flags;
>> +	u32 input_status;
>>   
>> +	spin_lock_irqsave(&video->lock, flags);
>> +	input_status = video->v4l2_input_status;
>>   	aspeed_video_on(video);
>>   
>>   	/* Exit early in case no clients remain */
>> -	if (test_bit(VIDEO_STOPPED, &video->flags))
>> +	if (test_bit(VIDEO_STOPPED, &video->flags)) {
>> +		spin_unlock_irqrestore(&video->lock, flags);
>>   		goto done;
>> +	}
>>   
>>   	aspeed_video_init_regs(video);
>> -
>> +	spin_unlock_irqrestore(&video->lock, flags);
>>   	aspeed_video_get_resolution(video);
>>   
>>   	if (video->detected_timings.width != video-
>>> active_timings.width ||
>
Benjamin Herrenschmidt - May 9, 2019, 1:08 a.m.
On Wed, 2019-05-08 at 15:19 -0700, Jae Hyun Yoo wrote:
> On 5/7/2019 11:31 PM, Benjamin Herrenschmidt wrote:
> > On Thu, 2019-05-02 at 12:13 -0700, Jae Hyun Yoo wrote:
> > > Video engine clock control functions in the Aspeed video engine
> > > driver are being called from multiple context without any
> > > protection so video clocks can be double disabled and eventually
> > > it causes a kernel warning with stack dump printing out like
> > > below:
> > 
> > I already objected to the use of set_bit, clear_bit etc...
> > 
> > Either you are protected by a spinlock, in which case you don't
> > need
> > them, use either the __ versions (non atomic) or just a bloody bool
> > flag which is a lot clearer and will generated better code. Or you
> > aren't protected in which case the code seems racy.
> 
> Got it. I'll use __set_bit and __clear_bit instead. Thanks for
> your pointing it out.

Why not a bool ? Any reason why you prefer bitops ? They are a bit of
an old-fashioned way of doing things unless you are actively trying to
save space by craming several flags in the same word.

Note: If you do the latter, ensure all users are properly locked, dont'
mix the __set_bit and set_bit variants on the same word.

Cheers,
Ben.
> Regards,
> Jae
> 
> > > [  515.540498] ------------[ cut here ]------------
> > > [  515.545174] WARNING: CPU: 0 PID: 1310 at drivers/clk/clk.c:684
> > > clk_core_unprepare+0x13c/0x170
> > > [  515.553806] vclk-gate already unprepared
> > > [  515.557841] CPU: 0 PID: 1310 Comm: obmc-ikvm Tainted:
> > > G        W         5.0.6-df66fbc97853fbba90a0bfa44de32f3d5f7602b4 
> > > #1
> > > [  515.568973] Hardware name: Generic DT based system
> > > [  515.573777] Backtrace:
> > > [  515.576272] [<80107cdc>] (dump_backtrace) from [<80107f10>]
> > > (show_stack+0x20/0x24)
> > > [  515.583930]  r7:803a5614 r6:00000009 r5:00000000 r4:9d88fe1c
> > > [  515.589712] [<80107ef0>] (show_stack) from [<80690184>]
> > > (dump_stack+0x20/0x28)
> > > [  515.597053] [<80690164>] (dump_stack) from [<80116044>]
> > > (__warn.part.3+0xb4/0xdc)
> > > [  515.604557] [<80115f90>] (__warn.part.3) from [<801160d8>]
> > > (warn_slowpath_fmt+0x6c/0x90)
> > > [  515.612734]  r6:000002ac r5:8080befc r4:80a07008
> > > [  515.617463] [<80116070>] (warn_slowpath_fmt) from [<803a5614>]
> > > (clk_core_unprepare+0x13c/0x170)
> > > [  515.626167]  r3:8080cdf4 r2:8080bfc0
> > > [  515.629834]  r7:98d682a8 r6:9d8a9200 r5:9e5151a0 r4:97abd620
> > > [  515.635530] [<803a54d8>] (clk_core_unprepare) from
> > > [<803a76a4>]
> > > (clk_unprepare+0x34/0x3c)
> > > [  515.643812]  r5:9e5151a0 r4:97abd620
> > > [  515.647529] [<803a7670>] (clk_unprepare) from [<804f36ec>]
> > > (aspeed_video_off+0x38/0x50)
> > > [  515.655539]  r5:9e5151a0 r4:9e504000
> > > [  515.659242] [<804f36b4>] (aspeed_video_off) from [<804f4358>]
> > > (aspeed_video_release+0x90/0x114)
> > > [  515.668036]  r5:9e5044b0 r4:9e504000
> > > [  515.671643] [<804f42c8>] (aspeed_video_release) from
> > > [<804d302c>]
> > > (v4l2_release+0xd4/0xe8)
> > > [  515.679999]  r7:98d682a8 r6:9d087810 r5:9d8a9200 r4:9e504318
> > > [  515.685695] [<804d2f58>] (v4l2_release) from [<80236454>]
> > > (__fput+0x98/0x1c4)
> > > [  515.692914]  r5:9e51b608 r4:9d8a9200
> > > [  515.696597] [<802363bc>] (__fput) from [<802365e8>]
> > > (____fput+0x18/0x1c)
> > > [  515.703315]  r9:80a0700c r8:801011e4 r7:00000000 r6:80a64b9c
> > > r5:9d8e35a0 r4:9d8e38dc
> > > [  515.711167] [<802365d0>] (____fput) from [<80131ca4>]
> > > (task_work_run+0x7c/0xa0)
> > > [  515.718596] [<80131c28>] (task_work_run) from [<80106884>]
> > > (do_work_pending+0x4a8/0x578)
> > > [  515.726777]  r7:801011e4 r6:80a07008 r5:9d88ffb0 r4:ffffe000
> > > [  515.732466] [<801063dc>] (do_work_pending) from [<8010106c>]
> > > (slow_work_pending+0xc/0x20)
> > > [  515.740727] Exception stack(0x9d88ffb0 to 0x9d88fff8)
> > > [  515.745840] ffa0:                                     00000000
> > > 76f18094 00000000 00000000
> > > [  515.754122] ffc0: 00000007 00176778 7eda4c20 00000006 00000000
> > > 00000000 48e20fa4 00000000
> > > [  515.762386] ffe0: 00000002 7eda4b08 00000000 48f91efc 80000010
> > > 00000007
> > > [  515.769097]  r10:00000000 r9:9d88e000 r8:801011e4 r7:00000006
> > > r6:7eda4c20 r5:00176778
> > > [  515.777006]  r4:00000007
> > > [  515.779558] ---[ end trace 12c04aadef8afbbb ]---
> > > [  515.784176] ------------[ cut here ]------------
> > > [  515.788817] WARNING: CPU: 0 PID: 1310 at drivers/clk/clk.c:825
> > > clk_core_disable+0x18c/0x204
> > > [  515.797161] eclk-gate already disabled
> > > [  515.800916] CPU: 0 PID: 1310 Comm: obmc-ikvm Tainted:
> > > G        W         5.0.6-df66fbc97853fbba90a0bfa44de32f3d5f7602b4 
> > > #1
> > > [  515.811945] Hardware name: Generic DT based system
> > > [  515.816730] Backtrace:
> > > [  515.819210] [<80107cdc>] (dump_backtrace) from [<80107f10>]
> > > (show_stack+0x20/0x24)
> > > [  515.826782]  r7:803a5900 r6:00000009 r5:00000000 r4:9d88fe04
> > > [  515.832454] [<80107ef0>] (show_stack) from [<80690184>]
> > > (dump_stack+0x20/0x28)
> > > [  515.839687] [<80690164>] (dump_stack) from [<80116044>]
> > > (__warn.part.3+0xb4/0xdc)
> > > [  515.847170] [<80115f90>] (__warn.part.3) from [<801160d8>]
> > > (warn_slowpath_fmt+0x6c/0x90)
> > > [  515.855247]  r6:00000339 r5:8080befc r4:80a07008
> > > [  515.859868] [<80116070>] (warn_slowpath_fmt) from [<803a5900>]
> > > (clk_core_disable+0x18c/0x204)
> > > [  515.868385]  r3:8080cdd0 r2:8080c00c
> > > [  515.871957]  r7:98d682a8 r6:9d8a9200 r5:97abd560 r4:97abd560
> > > [  515.877615] [<803a5774>] (clk_core_disable) from [<803a59a0>]
> > > (clk_core_disable_lock+0x28/0x34)
> > > [  515.886301]  r7:98d682a8 r6:9d8a9200 r5:97abd560 r4:a0000013
> > > [  515.891960] [<803a5978>] (clk_core_disable_lock) from
> > > [<803a7714>]
> > > (clk_disable+0x2c/0x30)
> > > [  515.900216]  r5:9e5151a0 r4:9e515f60
> > > [  515.903816] [<803a76e8>] (clk_disable) from [<804f36f8>]
> > > (aspeed_video_off+0x44/0x50)
> > > [  515.911656] [<804f36b4>] (aspeed_video_off) from [<804f4358>]
> > > (aspeed_video_release+0x90/0x114)
> > > [  515.920341]  r5:9e5044b0 r4:9e504000
> > > [  515.923921] [<804f42c8>] (aspeed_video_release) from
> > > [<804d302c>]
> > > (v4l2_release+0xd4/0xe8)
> > > [  515.932184]  r7:98d682a8 r6:9d087810 r5:9d8a9200 r4:9e504318
> > > [  515.937851] [<804d2f58>] (v4l2_release) from [<80236454>]
> > > (__fput+0x98/0x1c4)
> > > [  515.944980]  r5:9e51b608 r4:9d8a9200
> > > [  515.948559] [<802363bc>] (__fput) from [<802365e8>]
> > > (____fput+0x18/0x1c)
> > > [  515.955257]  r9:80a0700c r8:801011e4 r7:00000000 r6:80a64b9c
> > > r5:9d8e35a0 r4:9d8e38dc
> > > [  515.963008] [<802365d0>] (____fput) from [<80131ca4>]
> > > (task_work_run+0x7c/0xa0)
> > > [  515.970333] [<80131c28>] (task_work_run) from [<80106884>]
> > > (do_work_pending+0x4a8/0x578)
> > > [  515.978421]  r7:801011e4 r6:80a07008 r5:9d88ffb0 r4:ffffe000
> > > [  515.984086] [<801063dc>] (do_work_pending) from [<8010106c>]
> > > (slow_work_pending+0xc/0x20)
> > > [  515.992247] Exception stack(0x9d88ffb0 to 0x9d88fff8)
> > > [  515.997296] ffa0:                                     00000000
> > > 76f18094 00000000 00000000
> > > [  516.005473] ffc0: 00000007 00176778 7eda4c20 00000006 00000000
> > > 00000000 48e20fa4 00000000
> > > [  516.013642] ffe0: 00000002 7eda4b08 00000000 48f91efc 80000010
> > > 00000007
> > > [  516.020257]  r10:00000000 r9:9d88e000 r8:801011e4 r7:00000006
> > > r6:7eda4c20 r5:00176778
> > > [  516.028072]  r4:00000007
> > > [  516.030606] ---[ end trace 12c04aadef8afbbc ]---
> > > 
> > > To prevent this issue, this commit adds spinlock protection and
> > > clock status checking logic into the Aspeed video engine driver.
> > > 
> > > Signed-off-by: Jae Hyun Yoo <jae.hyun.yoo@linux.intel.com>
> > > Reviewed-by: Eddie James <eajames@linux.ibm.com>
> > > ---
> > >   drivers/media/platform/aspeed-video.c | 32
> > > ++++++++++++++++++++++++-
> > > --
> > >   1 file changed, 29 insertions(+), 3 deletions(-)
> > > 
> > > diff --git a/drivers/media/platform/aspeed-video.c
> > > b/drivers/media/platform/aspeed-video.c
> > > index 55c55a68b016..2dac6d20b180 100644
> > > --- a/drivers/media/platform/aspeed-video.c
> > > +++ b/drivers/media/platform/aspeed-video.c
> > > @@ -187,6 +187,7 @@ enum {
> > >   	VIDEO_STREAMING,
> > >   	VIDEO_FRAME_INPRG,
> > >   	VIDEO_STOPPED,
> > > +	VIDEO_CLOCKS_ON,
> > >   };
> > >   
> > >   struct aspeed_video_addr {
> > > @@ -483,19 +484,29 @@ static void
> > > aspeed_video_enable_mode_detect(struct aspeed_video *video)
> > >   
> > >   static void aspeed_video_off(struct aspeed_video *video)
> > >   {
> > > +	if (!test_bit(VIDEO_CLOCKS_ON, &video->flags))
> > > +		return;
> > > +
> > >   	/* Disable interrupts */
> > >   	aspeed_video_write(video, VE_INTERRUPT_CTRL, 0);
> > >   
> > >   	/* Turn off the relevant clocks */
> > >   	clk_disable_unprepare(video->vclk);
> > >   	clk_disable_unprepare(video->eclk);
> > > +
> > > +	clear_bit(VIDEO_CLOCKS_ON, &video->flags);
> > >   }
> > >   
> > >   static void aspeed_video_on(struct aspeed_video *video)
> > >   {
> > > +	if (test_bit(VIDEO_CLOCKS_ON, &video->flags))
> > > +		return;
> > > +
> > >   	/* Turn on the relevant clocks */
> > >   	clk_prepare_enable(video->eclk);
> > >   	clk_prepare_enable(video->vclk);
> > > +
> > > +	set_bit(VIDEO_CLOCKS_ON, &video->flags);
> > >   }
> > >   
> > >   static void aspeed_video_bufs_done(struct aspeed_video *video,
> > > @@ -513,12 +524,14 @@ static void aspeed_video_bufs_done(struct
> > > aspeed_video *video,
> > >   
> > >   static void aspeed_video_irq_res_change(struct aspeed_video
> > > *video)
> > >   {
> > > +	spin_lock(&video->lock);
> > >   	dev_dbg(video->dev, "Resolution changed; resetting\n");
> > >   
> > >   	set_bit(VIDEO_RES_CHANGE, &video->flags);
> > >   	clear_bit(VIDEO_FRAME_INPRG, &video->flags);
> > >   
> > >   	aspeed_video_off(video);
> > > +	spin_unlock(&video->lock);
> > >   	aspeed_video_bufs_done(video, VB2_BUF_STATE_ERROR);
> > >   
> > >   	schedule_delayed_work(&video->res_work,
> > > RESOLUTION_CHANGE_DELAY);
> > > @@ -938,9 +951,13 @@ static void aspeed_video_init_regs(struct
> > > aspeed_video *video)
> > >   
> > >   static void aspeed_video_start(struct aspeed_video *video)
> > >   {
> > > +	unsigned long flags;
> > > +
> > > +	spin_lock_irqsave(&video->lock, flags);
> > >   	aspeed_video_on(video);
> > >   
> > >   	aspeed_video_init_regs(video);
> > > +	spin_unlock_irqrestore(&video->lock, flags);
> > >   
> > >   	/* Resolution set to 640x480 if no signal found */
> > >   	aspeed_video_get_resolution(video);
> > > @@ -956,6 +973,9 @@ static void aspeed_video_start(struct
> > > aspeed_video *video)
> > >   
> > >   static void aspeed_video_stop(struct aspeed_video *video)
> > >   {
> > > +	unsigned long flags;
> > > +
> > > +	spin_lock_irqsave(&video->lock, flags);
> > >   	set_bit(VIDEO_STOPPED, &video->flags);
> > >   	cancel_delayed_work_sync(&video->res_work);
> > >   
> > > @@ -969,6 +989,7 @@ static void aspeed_video_stop(struct
> > > aspeed_video
> > > *video)
> > >   
> > >   	video->v4l2_input_status = V4L2_IN_ST_NO_SIGNAL;
> > >   	video->flags = 0;
> > > +	spin_unlock_irqrestore(&video->lock, flags);
> > >   }
> > >   
> > >   static int aspeed_video_querycap(struct file *file, void *fh,
> > > @@ -1306,16 +1327,21 @@ static void
> > > aspeed_video_resolution_work(struct work_struct *work)
> > >   	struct delayed_work *dwork = to_delayed_work(work);
> > >   	struct aspeed_video *video = container_of(dwork, struct
> > > aspeed_video,
> > >   						  res_work);
> > > -	u32 input_status = video->v4l2_input_status;
> > > +	unsigned long flags;
> > > +	u32 input_status;
> > >   
> > > +	spin_lock_irqsave(&video->lock, flags);
> > > +	input_status = video->v4l2_input_status;
> > >   	aspeed_video_on(video);
> > >   
> > >   	/* Exit early in case no clients remain */
> > > -	if (test_bit(VIDEO_STOPPED, &video->flags))
> > > +	if (test_bit(VIDEO_STOPPED, &video->flags)) {
> > > +		spin_unlock_irqrestore(&video->lock, flags);
> > >   		goto done;
> > > +	}
> > >   
> > >   	aspeed_video_init_regs(video);
> > > -
> > > +	spin_unlock_irqrestore(&video->lock, flags);
> > >   	aspeed_video_get_resolution(video);
> > >   
> > >   	if (video->detected_timings.width != video-
> > > > active_timings.width ||
Benjamin Herrenschmidt - May 9, 2019, 2:16 a.m.
On Wed, 2019-05-08 at 18:19 -0700, Jae Hyun Yoo wrote:
> I changed that from a bool because the maintainer of this code, Eddie
> doesn't like adding of an additional flag. I'll change it back with
> codes in the first submit:
> https://www.spinics.net/lists/linux-media/msg148955.html
> 
> Eddie,
> Please let me know if you have any objection on that.

Ok, so random flags ... ugh.

Well, you can approach it either way. Have them all be bitops or all be
bool.

The tricky thing however is that if they are bitops you need to ensure
that they are *all* manipulated under the same lock. If not you have to
use the atomic bitops variants.

The reason I don't like that is that experience shows that most uses of
such atomic variants in drivers usually are failed attempts at papering
over broken locking.

If everything is covered by a lock, then using the non-atomic versions
is more efficient, but so is using bool (optionally with :1 bitfield
qualifiers to avoid wasting memory), which from a pure C language
perspective I think is more expressive of what you are doing and more
readable.

Cheers,
Ben.
Eddie James - May 9, 2019, 3:19 p.m.
On 5/8/19 9:16 PM, Benjamin Herrenschmidt wrote:
> On Wed, 2019-05-08 at 18:19 -0700, Jae Hyun Yoo wrote:
>> I changed that from a bool because the maintainer of this code, Eddie
>> doesn't like adding of an additional flag. I'll change it back with
>> codes in the first submit:
>> https://www.spinics.net/lists/linux-media/msg148955.html
>>
>> Eddie,
>> Please let me know if you have any objection on that.


Thats fine with me. I merely thought it was more conventional to use 
flags rather than bools, but I may be mistaken.

Thanks!

Eddie


> Ok, so random flags ... ugh.
>
> Well, you can approach it either way. Have them all be bitops or all be
> bool.
>
> The tricky thing however is that if they are bitops you need to ensure
> that they are *all* manipulated under the same lock. If not you have to
> use the atomic bitops variants.
>
> The reason I don't like that is that experience shows that most uses of
> such atomic variants in drivers usually are failed attempts at papering
> over broken locking.
>
> If everything is covered by a lock, then using the non-atomic versions
> is more efficient, but so is using bool (optionally with :1 bitfield
> qualifiers to avoid wasting memory), which from a pure C language
> perspective I think is more expressive of what you are doing and more
> readable.
>
> Cheers,
> Ben.
>
Jae Hyun Yoo - May 9, 2019, 5:19 p.m.
On 5/8/2019 7:16 PM, Benjamin Herrenschmidt wrote:
> On Wed, 2019-05-08 at 18:19 -0700, Jae Hyun Yoo wrote:
>> I changed that from a bool because the maintainer of this code, Eddie
>> doesn't like adding of an additional flag. I'll change it back with
>> codes in the first submit:
>> https://www.spinics.net/lists/linux-media/msg148955.html
>>
>> Eddie,
>> Please let me know if you have any objection on that.
> 
> Ok, so random flags ... ugh.
> 
> Well, you can approach it either way. Have them all be bitops or all be
> bool.
> 
> The tricky thing however is that if they are bitops you need to ensure
> that they are *all* manipulated under the same lock. If not you have to
> use the atomic bitops variants.
> 
> The reason I don't like that is that experience shows that most uses of
> such atomic variants in drivers usually are failed attempts at papering
> over broken locking.
> 
> If everything is covered by a lock, then using the non-atomic versions
> is more efficient, but so is using bool (optionally with :1 bitfield
> qualifiers to avoid wasting memory), which from a pure C language
> perspective I think is more expressive of what you are doing and more
> readable.

Okay. Probably I need to add one another patch in this series to address
what you pointed out.

I have one question. I reviewed again all bitops in this driver and
checked that some bitops are protected by a spinlock and some others
are not. In this case, can I mix use atomic and non-atomic bitops
depend on each bitop's protection state by the spinlock? Or, would it be
better to change all of them to bool in this case?

Thanks,
Jae

> 
> Cheers,
> Ben.
>
Benjamin Herrenschmidt - May 9, 2019, 11:19 p.m.
On Thu, 2019-05-09 at 10:19 -0700, Jae Hyun Yoo wrote:
> 
> Okay. Probably I need to add one another patch in this series to address
> what you pointed out.
> 
> I have one question. I reviewed again all bitops in this driver and
> checked that some bitops are protected by a spinlock and some others
> are not. In this case, can I mix use atomic and non-atomic bitops
> depend on each bitop's protection state by the spinlock? Or, would it be
> better to change all of them to bool in this case?

No, if some aren't protected by a lock and some are, then they need to
remain atomic.

The question then becomes whether the unprotected ones are actually
correct or just exposing more races.

Cheers,
Ben.
Jae Hyun Yoo - May 9, 2019, 11:51 p.m.
On 5/9/2019 4:19 PM, Benjamin Herrenschmidt wrote:
> On Thu, 2019-05-09 at 10:19 -0700, Jae Hyun Yoo wrote:
>>
>> Okay. Probably I need to add one another patch in this series to address
>> what you pointed out.
>>
>> I have one question. I reviewed again all bitops in this driver and
>> checked that some bitops are protected by a spinlock and some others
>> are not. In this case, can I mix use atomic and non-atomic bitops
>> depend on each bitop's protection state by the spinlock? Or, would it be
>> better to change all of them to bool in this case?
> 
> No, if some aren't protected by a lock and some are, then they need to
> remain atomic.
> 
> The question then becomes whether the unprotected ones are actually
> correct or just exposing more races.

Got it. Not sure yet but I think the protected bitops could be moved out
from the spinlock scope then all bitops could be kept as atomic. I'll
look at and test this driver code more deeply again, and will submit v2
soon.

Again, thanks a lot for your review.

Regards,
Jae
Benjamin Herrenschmidt - May 10, 2019, 3:01 a.m.
On Thu, 2019-05-09 at 16:51 -0700, Jae Hyun Yoo wrote:
> On 5/9/2019 4:19 PM, Benjamin Herrenschmidt wrote:
> > On Thu, 2019-05-09 at 10:19 -0700, Jae Hyun Yoo wrote:
> > > 
> > > Okay. Probably I need to add one another patch in this series to
> > > address
> > > what you pointed out.
> > > 
> > > I have one question. I reviewed again all bitops in this driver
> > > and
> > > checked that some bitops are protected by a spinlock and some
> > > others
> > > are not. In this case, can I mix use atomic and non-atomic bitops
> > > depend on each bitop's protection state by the spinlock? Or,
> > > would it be
> > > better to change all of them to bool in this case?
> > 
> > No, if some aren't protected by a lock and some are, then they need
> > to
> > remain atomic.
> > 
> > The question then becomes whether the unprotected ones are actually
> > correct or just exposing more races.
> 
> Got it. Not sure yet but I think the protected bitops could be moved
> out
> from the spinlock scope then all bitops could be kept as atomic.

Which is very likely to be extremely racy... (and gratuitously more
costly) :-)

>  I'll
> look at and test this driver code more deeply again, and will submit
> v2
> soon.
> 
> Again, thanks a lot for your review.
> 
> Regards,
> Jae
Jae Hyun Yoo - May 10, 2019, 4:28 a.m.
On 5/9/2019 8:01 PM, Benjamin Herrenschmidt wrote:
> On Thu, 2019-05-09 at 16:51 -0700, Jae Hyun Yoo wrote:
>> On 5/9/2019 4:19 PM, Benjamin Herrenschmidt wrote:
>>> On Thu, 2019-05-09 at 10:19 -0700, Jae Hyun Yoo wrote:
>>>>
>>>> Okay. Probably I need to add one another patch in this series to
>>>> address
>>>> what you pointed out.
>>>>
>>>> I have one question. I reviewed again all bitops in this driver
>>>> and
>>>> checked that some bitops are protected by a spinlock and some
>>>> others
>>>> are not. In this case, can I mix use atomic and non-atomic bitops
>>>> depend on each bitop's protection state by the spinlock? Or,
>>>> would it be
>>>> better to change all of them to bool in this case?
>>>
>>> No, if some aren't protected by a lock and some are, then they need
>>> to
>>> remain atomic.
>>>
>>> The question then becomes whether the unprotected ones are actually
>>> correct or just exposing more races.
>>
>> Got it. Not sure yet but I think the protected bitops could be moved
>> out
>> from the spinlock scope then all bitops could be kept as atomic.
> 
> Which is very likely to be extremely racy... (and gratuitously more
> costly) :-)

Okay then, will try to wrap all bitops using a single spinlock and
change all of them to non-atomic bitops. Is it right approach?

Thanks,
Jae

>>   I'll
>> look at and test this driver code more deeply again, and will submit
>> v2
>> soon.
>>
>> Again, thanks a lot for your review.
>>
>> Regards,
>> Jae
>

Patch

diff --git a/drivers/media/platform/aspeed-video.c b/drivers/media/platform/aspeed-video.c
index 55c55a68b016..2dac6d20b180 100644
--- a/drivers/media/platform/aspeed-video.c
+++ b/drivers/media/platform/aspeed-video.c
@@ -187,6 +187,7 @@  enum {
 	VIDEO_STREAMING,
 	VIDEO_FRAME_INPRG,
 	VIDEO_STOPPED,
+	VIDEO_CLOCKS_ON,
 };
 
 struct aspeed_video_addr {
@@ -483,19 +484,29 @@  static void aspeed_video_enable_mode_detect(struct aspeed_video *video)
 
 static void aspeed_video_off(struct aspeed_video *video)
 {
+	if (!test_bit(VIDEO_CLOCKS_ON, &video->flags))
+		return;
+
 	/* Disable interrupts */
 	aspeed_video_write(video, VE_INTERRUPT_CTRL, 0);
 
 	/* Turn off the relevant clocks */
 	clk_disable_unprepare(video->vclk);
 	clk_disable_unprepare(video->eclk);
+
+	clear_bit(VIDEO_CLOCKS_ON, &video->flags);
 }
 
 static void aspeed_video_on(struct aspeed_video *video)
 {
+	if (test_bit(VIDEO_CLOCKS_ON, &video->flags))
+		return;
+
 	/* Turn on the relevant clocks */
 	clk_prepare_enable(video->eclk);
 	clk_prepare_enable(video->vclk);
+
+	set_bit(VIDEO_CLOCKS_ON, &video->flags);
 }
 
 static void aspeed_video_bufs_done(struct aspeed_video *video,
@@ -513,12 +524,14 @@  static void aspeed_video_bufs_done(struct aspeed_video *video,
 
 static void aspeed_video_irq_res_change(struct aspeed_video *video)
 {
+	spin_lock(&video->lock);
 	dev_dbg(video->dev, "Resolution changed; resetting\n");
 
 	set_bit(VIDEO_RES_CHANGE, &video->flags);
 	clear_bit(VIDEO_FRAME_INPRG, &video->flags);
 
 	aspeed_video_off(video);
+	spin_unlock(&video->lock);
 	aspeed_video_bufs_done(video, VB2_BUF_STATE_ERROR);
 
 	schedule_delayed_work(&video->res_work, RESOLUTION_CHANGE_DELAY);
@@ -938,9 +951,13 @@  static void aspeed_video_init_regs(struct aspeed_video *video)
 
 static void aspeed_video_start(struct aspeed_video *video)
 {
+	unsigned long flags;
+
+	spin_lock_irqsave(&video->lock, flags);
 	aspeed_video_on(video);
 
 	aspeed_video_init_regs(video);
+	spin_unlock_irqrestore(&video->lock, flags);
 
 	/* Resolution set to 640x480 if no signal found */
 	aspeed_video_get_resolution(video);
@@ -956,6 +973,9 @@  static void aspeed_video_start(struct aspeed_video *video)
 
 static void aspeed_video_stop(struct aspeed_video *video)
 {
+	unsigned long flags;
+
+	spin_lock_irqsave(&video->lock, flags);
 	set_bit(VIDEO_STOPPED, &video->flags);
 	cancel_delayed_work_sync(&video->res_work);
 
@@ -969,6 +989,7 @@  static void aspeed_video_stop(struct aspeed_video *video)
 
 	video->v4l2_input_status = V4L2_IN_ST_NO_SIGNAL;
 	video->flags = 0;
+	spin_unlock_irqrestore(&video->lock, flags);
 }
 
 static int aspeed_video_querycap(struct file *file, void *fh,
@@ -1306,16 +1327,21 @@  static void aspeed_video_resolution_work(struct work_struct *work)
 	struct delayed_work *dwork = to_delayed_work(work);
 	struct aspeed_video *video = container_of(dwork, struct aspeed_video,
 						  res_work);
-	u32 input_status = video->v4l2_input_status;
+	unsigned long flags;
+	u32 input_status;
 
+	spin_lock_irqsave(&video->lock, flags);
+	input_status = video->v4l2_input_status;
 	aspeed_video_on(video);
 
 	/* Exit early in case no clients remain */
-	if (test_bit(VIDEO_STOPPED, &video->flags))
+	if (test_bit(VIDEO_STOPPED, &video->flags)) {
+		spin_unlock_irqrestore(&video->lock, flags);
 		goto done;
+	}
 
 	aspeed_video_init_regs(video);
-
+	spin_unlock_irqrestore(&video->lock, flags);
 	aspeed_video_get_resolution(video);
 
 	if (video->detected_timings.width != video->active_timings.width ||

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