LinuxTV Patchwork dma-buf: fix debugfs versus rcu and fence dumping

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Submitter Jerome Glisse
Date Dec. 6, 2018, 1:41 a.m.
Message ID <20181206014103.1364-1-jglisse@redhat.com>
Download mbox | patch
Permalink /patch/53344/
State Not Applicable
Headers show

Comments

Jerome Glisse - Dec. 6, 2018, 1:41 a.m.
From: Jérôme Glisse <jglisse@redhat.com>

The debugfs take reference on fence without dropping them. Also the
rcu section are not well balance. Fix all that ...

Signed-off-by: Jérôme Glisse <jglisse@redhat.com>
Cc: Christian König <christian.koenig@amd.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Sumit Semwal <sumit.semwal@linaro.org>
Cc: linux-media@vger.kernel.org
Cc: dri-devel@lists.freedesktop.org
Cc: linaro-mm-sig@lists.linaro.org
Cc: Stéphane Marchesin <marcheu@chromium.org>
Cc: stable@vger.kernel.org
---
 drivers/dma-buf/dma-buf.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)
Christian König - Dec. 6, 2018, 8:09 a.m.
Am 06.12.18 um 02:41 schrieb jglisse@redhat.com:
> From: Jérôme Glisse <jglisse@redhat.com>

>

> The debugfs take reference on fence without dropping them. Also the

> rcu section are not well balance. Fix all that ...

>

> Signed-off-by: Jérôme Glisse <jglisse@redhat.com>

> Cc: Christian König <christian.koenig@amd.com>

> Cc: Daniel Vetter <daniel.vetter@ffwll.ch>

> Cc: Sumit Semwal <sumit.semwal@linaro.org>

> Cc: linux-media@vger.kernel.org

> Cc: dri-devel@lists.freedesktop.org

> Cc: linaro-mm-sig@lists.linaro.org

> Cc: Stéphane Marchesin <marcheu@chromium.org>

> Cc: stable@vger.kernel.org


Well NAK, you are now taking the RCU lock twice and dropping the RCU and 
still accessing fobj has a huge potential for accessing freed up memory.

The only correct thing I can see here is to grab a reference to the 
fence before printing any info on it,
Christian.

> ---

>   drivers/dma-buf/dma-buf.c | 11 +++++++++--

>   1 file changed, 9 insertions(+), 2 deletions(-)

>

> diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c

> index 13884474d158..f6f4de42ac49 100644

> --- a/drivers/dma-buf/dma-buf.c

> +++ b/drivers/dma-buf/dma-buf.c

> @@ -1051,24 +1051,31 @@ static int dma_buf_debug_show(struct seq_file *s, void *unused)

>   			fobj = rcu_dereference(robj->fence);

>   			shared_count = fobj ? fobj->shared_count : 0;

>   			fence = rcu_dereference(robj->fence_excl);

> +			fence = dma_fence_get_rcu(fence);

>   			if (!read_seqcount_retry(&robj->seq, seq))

>   				break;

>   			rcu_read_unlock();

>   		}

> -

> -		if (fence)

> +		if (fence) {

>   			seq_printf(s, "\tExclusive fence: %s %s %ssignalled\n",

>   				   fence->ops->get_driver_name(fence),

>   				   fence->ops->get_timeline_name(fence),

>   				   dma_fence_is_signaled(fence) ? "" : "un");

> +			dma_fence_put(fence);

> +		}

> +

> +		rcu_read_lock();

>   		for (i = 0; i < shared_count; i++) {

>   			fence = rcu_dereference(fobj->shared[i]);

>   			if (!dma_fence_get_rcu(fence))

>   				continue;

> +			rcu_read_unlock();

>   			seq_printf(s, "\tShared fence: %s %s %ssignalled\n",

>   				   fence->ops->get_driver_name(fence),

>   				   fence->ops->get_timeline_name(fence),

>   				   dma_fence_is_signaled(fence) ? "" : "un");

> +			dma_fence_put(fence);

> +			rcu_read_lock();

>   		}

>   		rcu_read_unlock();

>
Jerome Glisse - Dec. 6, 2018, 3:21 p.m.
On Thu, Dec 06, 2018 at 08:09:28AM +0000, Koenig, Christian wrote:
> Am 06.12.18 um 02:41 schrieb jglisse@redhat.com:
> > From: Jérôme Glisse <jglisse@redhat.com>
> >
> > The debugfs take reference on fence without dropping them. Also the
> > rcu section are not well balance. Fix all that ...
> >
> > Signed-off-by: Jérôme Glisse <jglisse@redhat.com>
> > Cc: Christian König <christian.koenig@amd.com>
> > Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
> > Cc: Sumit Semwal <sumit.semwal@linaro.org>
> > Cc: linux-media@vger.kernel.org
> > Cc: dri-devel@lists.freedesktop.org
> > Cc: linaro-mm-sig@lists.linaro.org
> > Cc: Stéphane Marchesin <marcheu@chromium.org>
> > Cc: stable@vger.kernel.org
> 
> Well NAK, you are now taking the RCU lock twice and dropping the RCU and 
> still accessing fobj has a huge potential for accessing freed up memory.
> 
> The only correct thing I can see here is to grab a reference to the 
> fence before printing any info on it,
> Christian.

Hu ? That is exactly what i am doing, take reference under rcu,
rcu_unlock print the fence info, drop the fence reference, rcu
lock rinse and repeat ...

Note that the fobj in _existing_ code is access outside the rcu
end that there is an rcu imbalance in that code ie a lonlely
rcu_unlock after the for loop.

So that the existing code is broken.

> 
> > ---
> >   drivers/dma-buf/dma-buf.c | 11 +++++++++--
> >   1 file changed, 9 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
> > index 13884474d158..f6f4de42ac49 100644
> > --- a/drivers/dma-buf/dma-buf.c
> > +++ b/drivers/dma-buf/dma-buf.c
> > @@ -1051,24 +1051,31 @@ static int dma_buf_debug_show(struct seq_file *s, void *unused)
> >   			fobj = rcu_dereference(robj->fence);
> >   			shared_count = fobj ? fobj->shared_count : 0;
> >   			fence = rcu_dereference(robj->fence_excl);
> > +			fence = dma_fence_get_rcu(fence);
> >   			if (!read_seqcount_retry(&robj->seq, seq))
> >   				break;
> >   			rcu_read_unlock();
> >   		}
> > -
> > -		if (fence)
> > +		if (fence) {
> >   			seq_printf(s, "\tExclusive fence: %s %s %ssignalled\n",
> >   				   fence->ops->get_driver_name(fence),
> >   				   fence->ops->get_timeline_name(fence),
> >   				   dma_fence_is_signaled(fence) ? "" : "un");
> > +			dma_fence_put(fence);
> > +		}
> > +
> > +		rcu_read_lock();
> >   		for (i = 0; i < shared_count; i++) {
> >   			fence = rcu_dereference(fobj->shared[i]);
> >   			if (!dma_fence_get_rcu(fence))
> >   				continue;
> > +			rcu_read_unlock();
> >   			seq_printf(s, "\tShared fence: %s %s %ssignalled\n",
> >   				   fence->ops->get_driver_name(fence),
> >   				   fence->ops->get_timeline_name(fence),
> >   				   dma_fence_is_signaled(fence) ? "" : "un");
> > +			dma_fence_put(fence);
> > +			rcu_read_lock();
> >   		}
> >   		rcu_read_unlock();
> >   
>
Christian König - Dec. 6, 2018, 4:08 p.m.
Am 06.12.18 um 16:21 schrieb Jerome Glisse:
> On Thu, Dec 06, 2018 at 08:09:28AM +0000, Koenig, Christian wrote:

>> Am 06.12.18 um 02:41 schrieb jglisse@redhat.com:

>>> From: Jérôme Glisse <jglisse@redhat.com>

>>>

>>> The debugfs take reference on fence without dropping them. Also the

>>> rcu section are not well balance. Fix all that ...

>>>

>>> Signed-off-by: Jérôme Glisse <jglisse@redhat.com>

>>> Cc: Christian König <christian.koenig@amd.com>

>>> Cc: Daniel Vetter <daniel.vetter@ffwll.ch>

>>> Cc: Sumit Semwal <sumit.semwal@linaro.org>

>>> Cc: linux-media@vger.kernel.org

>>> Cc: dri-devel@lists.freedesktop.org

>>> Cc: linaro-mm-sig@lists.linaro.org

>>> Cc: Stéphane Marchesin <marcheu@chromium.org>

>>> Cc: stable@vger.kernel.org

>> Well NAK, you are now taking the RCU lock twice and dropping the RCU and

>> still accessing fobj has a huge potential for accessing freed up memory.

>>

>> The only correct thing I can see here is to grab a reference to the

>> fence before printing any info on it,

>> Christian.

> Hu ? That is exactly what i am doing, take reference under rcu,

> rcu_unlock print the fence info, drop the fence reference, rcu

> lock rinse and repeat ...

>

> Note that the fobj in _existing_ code is access outside the rcu

> end that there is an rcu imbalance in that code ie a lonlely

> rcu_unlock after the for loop.

>

> So that the existing code is broken.


No, the existing code is perfectly fine.

Please note the break in the loop before the rcu_unlock();
>    			if (!read_seqcount_retry(&robj->seq, seq))

>    				break; <- HERE!

>    			rcu_read_unlock();

>    		}


So your patch breaks that and take the RCU read lock twice.

Regards,
Christian.

>

>>> ---

>>>    drivers/dma-buf/dma-buf.c | 11 +++++++++--

>>>    1 file changed, 9 insertions(+), 2 deletions(-)

>>>

>>> diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c

>>> index 13884474d158..f6f4de42ac49 100644

>>> --- a/drivers/dma-buf/dma-buf.c

>>> +++ b/drivers/dma-buf/dma-buf.c

>>> @@ -1051,24 +1051,31 @@ static int dma_buf_debug_show(struct seq_file *s, void *unused)

>>>    			fobj = rcu_dereference(robj->fence);

>>>    			shared_count = fobj ? fobj->shared_count : 0;

>>>    			fence = rcu_dereference(robj->fence_excl);

>>> +			fence = dma_fence_get_rcu(fence);

>>>    			if (!read_seqcount_retry(&robj->seq, seq))

>>>    				break;

>>>    			rcu_read_unlock();

>>>    		}

>>> -

>>> -		if (fence)

>>> +		if (fence) {

>>>    			seq_printf(s, "\tExclusive fence: %s %s %ssignalled\n",

>>>    				   fence->ops->get_driver_name(fence),

>>>    				   fence->ops->get_timeline_name(fence),

>>>    				   dma_fence_is_signaled(fence) ? "" : "un");

>>> +			dma_fence_put(fence);

>>> +		}

>>> +

>>> +		rcu_read_lock();

>>>    		for (i = 0; i < shared_count; i++) {

>>>    			fence = rcu_dereference(fobj->shared[i]);

>>>    			if (!dma_fence_get_rcu(fence))

>>>    				continue;

>>> +			rcu_read_unlock();

>>>    			seq_printf(s, "\tShared fence: %s %s %ssignalled\n",

>>>    				   fence->ops->get_driver_name(fence),

>>>    				   fence->ops->get_timeline_name(fence),

>>>    				   dma_fence_is_signaled(fence) ? "" : "un");

>>> +			dma_fence_put(fence);

>>> +			rcu_read_lock();

>>>    		}

>>>    		rcu_read_unlock();

>>>
Jerome Glisse - Dec. 6, 2018, 4:19 p.m.
On Thu, Dec 06, 2018 at 04:08:12PM +0000, Koenig, Christian wrote:
> Am 06.12.18 um 16:21 schrieb Jerome Glisse:
> > On Thu, Dec 06, 2018 at 08:09:28AM +0000, Koenig, Christian wrote:
> >> Am 06.12.18 um 02:41 schrieb jglisse@redhat.com:
> >>> From: Jérôme Glisse <jglisse@redhat.com>
> >>>
> >>> The debugfs take reference on fence without dropping them. Also the
> >>> rcu section are not well balance. Fix all that ...
> >>>
> >>> Signed-off-by: Jérôme Glisse <jglisse@redhat.com>
> >>> Cc: Christian König <christian.koenig@amd.com>
> >>> Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
> >>> Cc: Sumit Semwal <sumit.semwal@linaro.org>
> >>> Cc: linux-media@vger.kernel.org
> >>> Cc: dri-devel@lists.freedesktop.org
> >>> Cc: linaro-mm-sig@lists.linaro.org
> >>> Cc: Stéphane Marchesin <marcheu@chromium.org>
> >>> Cc: stable@vger.kernel.org
> >> Well NAK, you are now taking the RCU lock twice and dropping the RCU and
> >> still accessing fobj has a huge potential for accessing freed up memory.
> >>
> >> The only correct thing I can see here is to grab a reference to the
> >> fence before printing any info on it,
> >> Christian.
> > Hu ? That is exactly what i am doing, take reference under rcu,
> > rcu_unlock print the fence info, drop the fence reference, rcu
> > lock rinse and repeat ...
> >
> > Note that the fobj in _existing_ code is access outside the rcu
> > end that there is an rcu imbalance in that code ie a lonlely
> > rcu_unlock after the for loop.
> >
> > So that the existing code is broken.
> 
> No, the existing code is perfectly fine.
> 
> Please note the break in the loop before the rcu_unlock();
> >    			if (!read_seqcount_retry(&robj->seq, seq))
> >    				break; <- HERE!
> >    			rcu_read_unlock();
> >    		}
> 
> So your patch breaks that and take the RCU read lock twice.

Ok missed that, i wonder if the refcount in balance explains
the crash that was reported to me ... i sent a patch just for
that.

Thank you for reviewing and pointing out the code i was
oblivious too :)

Cheers,
Jérôme
kbuild test robot - Dec. 16, 2018, 7:23 p.m.
Hi Jérôme,

I love your patch! Perhaps something to improve:

[auto build test WARNING on linus/master]
[also build test WARNING on v4.20-rc6 next-20181214]
[if your patch is applied to the wrong git tree, please drop us a note to help improve the system]

url:    https://github.com/0day-ci/linux/commits/jglisse-redhat-com/dma-buf-fix-debugfs-versus-rcu-and-fence-dumping/20181206-205935
config: x86_64-allmodconfig (attached as .config)
compiler: gcc-7 (Debian 7.3.0-1) 7.3.0
reproduce:
        # save the attached .config to linux build tree
        make ARCH=x86_64 

All warnings (new ones prefixed by >>):

   include/linux/slab.h:332:43: warning: dubious: x & !y
   include/linux/slab.h:332:43: warning: dubious: x & !y
>> drivers/dma-buf/dma-buf.c:1031:9: warning: context imbalance in 'dma_buf_debug_show' - different lock contexts for basic block

vim +/dma_buf_debug_show +1031 drivers/dma-buf/dma-buf.c

b89e3563 drivers/base/dma-buf.c    Sumit Semwal   2013-04-04  1008  
b89e3563 drivers/base/dma-buf.c    Sumit Semwal   2013-04-04  1009  #ifdef CONFIG_DEBUG_FS
eb0b947e drivers/dma-buf/dma-buf.c Mathias Krause 2016-06-19  1010  static int dma_buf_debug_show(struct seq_file *s, void *unused)
b89e3563 drivers/base/dma-buf.c    Sumit Semwal   2013-04-04  1011  {
b89e3563 drivers/base/dma-buf.c    Sumit Semwal   2013-04-04  1012  	int ret;
b89e3563 drivers/base/dma-buf.c    Sumit Semwal   2013-04-04  1013  	struct dma_buf *buf_obj;
b89e3563 drivers/base/dma-buf.c    Sumit Semwal   2013-04-04  1014  	struct dma_buf_attachment *attach_obj;
5eb2c72c drivers/dma-buf/dma-buf.c Russell King   2017-03-31  1015  	struct reservation_object *robj;
5eb2c72c drivers/dma-buf/dma-buf.c Russell King   2017-03-31  1016  	struct reservation_object_list *fobj;
5eb2c72c drivers/dma-buf/dma-buf.c Russell King   2017-03-31  1017  	struct dma_fence *fence;
5eb2c72c drivers/dma-buf/dma-buf.c Russell King   2017-03-31  1018  	unsigned seq;
5eb2c72c drivers/dma-buf/dma-buf.c Russell King   2017-03-31  1019  	int count = 0, attach_count, shared_count, i;
b89e3563 drivers/base/dma-buf.c    Sumit Semwal   2013-04-04  1020  	size_t size = 0;
b89e3563 drivers/base/dma-buf.c    Sumit Semwal   2013-04-04  1021  
b89e3563 drivers/base/dma-buf.c    Sumit Semwal   2013-04-04  1022  	ret = mutex_lock_interruptible(&db_list.lock);
b89e3563 drivers/base/dma-buf.c    Sumit Semwal   2013-04-04  1023  
b89e3563 drivers/base/dma-buf.c    Sumit Semwal   2013-04-04  1024  	if (ret)
b89e3563 drivers/base/dma-buf.c    Sumit Semwal   2013-04-04  1025  		return ret;
b89e3563 drivers/base/dma-buf.c    Sumit Semwal   2013-04-04  1026  
c0b00a52 drivers/base/dma-buf.c    Sumit Semwal   2014-02-03  1027  	seq_puts(s, "\nDma-buf Objects:\n");
da6c8f5e drivers/dma-buf/dma-buf.c Russell King   2017-03-31  1028  	seq_printf(s, "%-8s\t%-8s\t%-8s\t%-8s\texp_name\n",
da6c8f5e drivers/dma-buf/dma-buf.c Russell King   2017-03-31  1029  		   "size", "flags", "mode", "count");
b89e3563 drivers/base/dma-buf.c    Sumit Semwal   2013-04-04  1030  
b89e3563 drivers/base/dma-buf.c    Sumit Semwal   2013-04-04 @1031  	list_for_each_entry(buf_obj, &db_list.head, list_node) {
b89e3563 drivers/base/dma-buf.c    Sumit Semwal   2013-04-04  1032  		ret = mutex_lock_interruptible(&buf_obj->lock);
b89e3563 drivers/base/dma-buf.c    Sumit Semwal   2013-04-04  1033  
b89e3563 drivers/base/dma-buf.c    Sumit Semwal   2013-04-04  1034  		if (ret) {
c0b00a52 drivers/base/dma-buf.c    Sumit Semwal   2014-02-03  1035  			seq_puts(s,
b89e3563 drivers/base/dma-buf.c    Sumit Semwal   2013-04-04  1036  				 "\tERROR locking buffer object: skipping\n");
b89e3563 drivers/base/dma-buf.c    Sumit Semwal   2013-04-04  1037  			continue;
b89e3563 drivers/base/dma-buf.c    Sumit Semwal   2013-04-04  1038  		}
b89e3563 drivers/base/dma-buf.c    Sumit Semwal   2013-04-04  1039  
c0b00a52 drivers/base/dma-buf.c    Sumit Semwal   2014-02-03  1040  		seq_printf(s, "%08zu\t%08x\t%08x\t%08ld\t%s\n",
c0b00a52 drivers/base/dma-buf.c    Sumit Semwal   2014-02-03  1041  				buf_obj->size,
b89e3563 drivers/base/dma-buf.c    Sumit Semwal   2013-04-04  1042  				buf_obj->file->f_flags, buf_obj->file->f_mode,
a1f6dbac drivers/dma-buf/dma-buf.c Al Viro        2014-08-20  1043  				file_count(buf_obj->file),
c0b00a52 drivers/base/dma-buf.c    Sumit Semwal   2014-02-03  1044  				buf_obj->exp_name);
b89e3563 drivers/base/dma-buf.c    Sumit Semwal   2013-04-04  1045  
5eb2c72c drivers/dma-buf/dma-buf.c Russell King   2017-03-31  1046  		robj = buf_obj->resv;
5eb2c72c drivers/dma-buf/dma-buf.c Russell King   2017-03-31  1047  		while (true) {
5eb2c72c drivers/dma-buf/dma-buf.c Russell King   2017-03-31  1048  			seq = read_seqcount_begin(&robj->seq);
5eb2c72c drivers/dma-buf/dma-buf.c Russell King   2017-03-31  1049  			rcu_read_lock();
5eb2c72c drivers/dma-buf/dma-buf.c Russell King   2017-03-31  1050  			fobj = rcu_dereference(robj->fence);
5eb2c72c drivers/dma-buf/dma-buf.c Russell King   2017-03-31  1051  			shared_count = fobj ? fobj->shared_count : 0;
5eb2c72c drivers/dma-buf/dma-buf.c Russell King   2017-03-31  1052  			fence = rcu_dereference(robj->fence_excl);
87e66c10 drivers/dma-buf/dma-buf.c Jérôme Glisse  2018-12-05  1053  			fence = dma_fence_get_rcu(fence);
5eb2c72c drivers/dma-buf/dma-buf.c Russell King   2017-03-31  1054  			if (!read_seqcount_retry(&robj->seq, seq))
5eb2c72c drivers/dma-buf/dma-buf.c Russell King   2017-03-31  1055  				break;
5eb2c72c drivers/dma-buf/dma-buf.c Russell King   2017-03-31  1056  			rcu_read_unlock();
5eb2c72c drivers/dma-buf/dma-buf.c Russell King   2017-03-31  1057  		}
87e66c10 drivers/dma-buf/dma-buf.c Jérôme Glisse  2018-12-05  1058  		if (fence) {
5eb2c72c drivers/dma-buf/dma-buf.c Russell King   2017-03-31  1059  			seq_printf(s, "\tExclusive fence: %s %s %ssignalled\n",
5eb2c72c drivers/dma-buf/dma-buf.c Russell King   2017-03-31  1060  				   fence->ops->get_driver_name(fence),
5eb2c72c drivers/dma-buf/dma-buf.c Russell King   2017-03-31  1061  				   fence->ops->get_timeline_name(fence),
5eb2c72c drivers/dma-buf/dma-buf.c Russell King   2017-03-31  1062  				   dma_fence_is_signaled(fence) ? "" : "un");
87e66c10 drivers/dma-buf/dma-buf.c Jérôme Glisse  2018-12-05  1063  			dma_fence_put(fence);
87e66c10 drivers/dma-buf/dma-buf.c Jérôme Glisse  2018-12-05  1064  		}
87e66c10 drivers/dma-buf/dma-buf.c Jérôme Glisse  2018-12-05  1065  
87e66c10 drivers/dma-buf/dma-buf.c Jérôme Glisse  2018-12-05  1066  		rcu_read_lock();
5eb2c72c drivers/dma-buf/dma-buf.c Russell King   2017-03-31  1067  		for (i = 0; i < shared_count; i++) {
5eb2c72c drivers/dma-buf/dma-buf.c Russell King   2017-03-31  1068  			fence = rcu_dereference(fobj->shared[i]);
5eb2c72c drivers/dma-buf/dma-buf.c Russell King   2017-03-31  1069  			if (!dma_fence_get_rcu(fence))
5eb2c72c drivers/dma-buf/dma-buf.c Russell King   2017-03-31  1070  				continue;
87e66c10 drivers/dma-buf/dma-buf.c Jérôme Glisse  2018-12-05  1071  			rcu_read_unlock();
5eb2c72c drivers/dma-buf/dma-buf.c Russell King   2017-03-31  1072  			seq_printf(s, "\tShared fence: %s %s %ssignalled\n",
5eb2c72c drivers/dma-buf/dma-buf.c Russell King   2017-03-31  1073  				   fence->ops->get_driver_name(fence),
5eb2c72c drivers/dma-buf/dma-buf.c Russell King   2017-03-31  1074  				   fence->ops->get_timeline_name(fence),
5eb2c72c drivers/dma-buf/dma-buf.c Russell King   2017-03-31  1075  				   dma_fence_is_signaled(fence) ? "" : "un");
87e66c10 drivers/dma-buf/dma-buf.c Jérôme Glisse  2018-12-05  1076  			dma_fence_put(fence);
87e66c10 drivers/dma-buf/dma-buf.c Jérôme Glisse  2018-12-05  1077  			rcu_read_lock();
5eb2c72c drivers/dma-buf/dma-buf.c Russell King   2017-03-31  1078  		}
5eb2c72c drivers/dma-buf/dma-buf.c Russell King   2017-03-31  1079  		rcu_read_unlock();
5eb2c72c drivers/dma-buf/dma-buf.c Russell King   2017-03-31  1080  
c0b00a52 drivers/base/dma-buf.c    Sumit Semwal   2014-02-03  1081  		seq_puts(s, "\tAttached Devices:\n");
b89e3563 drivers/base/dma-buf.c    Sumit Semwal   2013-04-04  1082  		attach_count = 0;
b89e3563 drivers/base/dma-buf.c    Sumit Semwal   2013-04-04  1083  
b89e3563 drivers/base/dma-buf.c    Sumit Semwal   2013-04-04  1084  		list_for_each_entry(attach_obj, &buf_obj->attachments, node) {
9eddb41d drivers/dma-buf/dma-buf.c Markus Elfring 2017-05-08  1085  			seq_printf(s, "\t%s\n", dev_name(attach_obj->dev));
b89e3563 drivers/base/dma-buf.c    Sumit Semwal   2013-04-04  1086  			attach_count++;
b89e3563 drivers/base/dma-buf.c    Sumit Semwal   2013-04-04  1087  		}
b89e3563 drivers/base/dma-buf.c    Sumit Semwal   2013-04-04  1088  
c0b00a52 drivers/base/dma-buf.c    Sumit Semwal   2014-02-03  1089  		seq_printf(s, "Total %d devices attached\n\n",
b89e3563 drivers/base/dma-buf.c    Sumit Semwal   2013-04-04  1090  				attach_count);
b89e3563 drivers/base/dma-buf.c    Sumit Semwal   2013-04-04  1091  
b89e3563 drivers/base/dma-buf.c    Sumit Semwal   2013-04-04  1092  		count++;
b89e3563 drivers/base/dma-buf.c    Sumit Semwal   2013-04-04  1093  		size += buf_obj->size;
b89e3563 drivers/base/dma-buf.c    Sumit Semwal   2013-04-04  1094  		mutex_unlock(&buf_obj->lock);
b89e3563 drivers/base/dma-buf.c    Sumit Semwal   2013-04-04  1095  	}
b89e3563 drivers/base/dma-buf.c    Sumit Semwal   2013-04-04  1096  
b89e3563 drivers/base/dma-buf.c    Sumit Semwal   2013-04-04  1097  	seq_printf(s, "\nTotal %d objects, %zu bytes\n", count, size);
b89e3563 drivers/base/dma-buf.c    Sumit Semwal   2013-04-04  1098  
b89e3563 drivers/base/dma-buf.c    Sumit Semwal   2013-04-04  1099  	mutex_unlock(&db_list.lock);
b89e3563 drivers/base/dma-buf.c    Sumit Semwal   2013-04-04  1100  	return 0;
b89e3563 drivers/base/dma-buf.c    Sumit Semwal   2013-04-04  1101  }
b89e3563 drivers/base/dma-buf.c    Sumit Semwal   2013-04-04  1102  

:::::: The code at line 1031 was first introduced by commit
:::::: b89e35636bc75b72d15a1af6d49798802aff77d5 dma-buf: Add debugfs support

:::::: TO: Sumit Semwal <sumit.semwal@linaro.org>
:::::: CC: Sumit Semwal <sumit.semwal@linaro.org>

---
0-DAY kernel test infrastructure                Open Source Technology Center
https://lists.01.org/pipermail/kbuild-all                   Intel Corporation

Patch

diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
index 13884474d158..f6f4de42ac49 100644
--- a/drivers/dma-buf/dma-buf.c
+++ b/drivers/dma-buf/dma-buf.c
@@ -1051,24 +1051,31 @@  static int dma_buf_debug_show(struct seq_file *s, void *unused)
 			fobj = rcu_dereference(robj->fence);
 			shared_count = fobj ? fobj->shared_count : 0;
 			fence = rcu_dereference(robj->fence_excl);
+			fence = dma_fence_get_rcu(fence);
 			if (!read_seqcount_retry(&robj->seq, seq))
 				break;
 			rcu_read_unlock();
 		}
-
-		if (fence)
+		if (fence) {
 			seq_printf(s, "\tExclusive fence: %s %s %ssignalled\n",
 				   fence->ops->get_driver_name(fence),
 				   fence->ops->get_timeline_name(fence),
 				   dma_fence_is_signaled(fence) ? "" : "un");
+			dma_fence_put(fence);
+		}
+
+		rcu_read_lock();
 		for (i = 0; i < shared_count; i++) {
 			fence = rcu_dereference(fobj->shared[i]);
 			if (!dma_fence_get_rcu(fence))
 				continue;
+			rcu_read_unlock();
 			seq_printf(s, "\tShared fence: %s %s %ssignalled\n",
 				   fence->ops->get_driver_name(fence),
 				   fence->ops->get_timeline_name(fence),
 				   dma_fence_is_signaled(fence) ? "" : "un");
+			dma_fence_put(fence);
+			rcu_read_lock();
 		}
 		rcu_read_unlock();
 

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