Re: [PATCH 1/1] ASoC: soc-compress: lock pcm_mutex to resolve lockdep error

[Vinod Koul <vkoul@kernel.org>]

On 31-03-20, 10:54, 이경택 wrote:
> Hi,
> 
> On 30-03-20, 17:17, Vinod Koul wrote:
> >Hello,
> >
> >On 30-03-20, 20:01,  ̰    wrote:
> >> snd_soc_runtime_activate() and snd_soc_runtime_deactivate() require 
> >> locked pcm_mutex.
> >> 
> >> Signed-off-by: Gyeongtaek Lee <gt82.lee@samsung.com>
> >> ---
> >>  sound/soc/soc-compress.c | 4 ++++
> >>  1 file changed, 4 insertions(+)
> >> 
> >> diff --git a/sound/soc/soc-compress.c b/sound/soc/soc-compress.c index 
> >> 392a1c5b15d3..42d416ac7e9b 100644
> >> --- a/sound/soc/soc-compress.c
> >> +++ b/sound/soc/soc-compress.c
> >> @@ -207,7 +207,9 @@ static int soc_compr_open_fe(struct 
> >> snd_compr_stream
> >> *cstream)
> >>  	fe->dpcm[stream].state = SND_SOC_DPCM_STATE_OPEN;
> >>  	fe->dpcm[stream].runtime_update = SND_SOC_DPCM_UPDATE_NO;
> >>  
> >> +	mutex_lock_nested(&fe->pcm_mutex, fe->pcm_subclass);
> >>  	snd_soc_runtime_activate(fe, stream);
> >> +	mutex_unlock(&fe->pcm_mutex);
> >
> >Can you please explain why you need the lock here, as
> >>  
> >>  	mutex_unlock(&fe->card->mutex);
> >
> >we already have a lock here..
> >
> >> @@ -285,7 +287,9 @@ static int soc_compr_free_fe(struct 
> >> snd_compr_stream
> >> *cstream)
> >>  	else
> >>  		stream = SNDRV_PCM_STREAM_CAPTURE;
> >>  
> >> +	mutex_lock_nested(&fe->pcm_mutex, fe->pcm_subclass);
> >>  	snd_soc_runtime_deactivate(fe, stream);
> >> +	mutex_unlock(&fe->pcm_mutex);
> >
> >And this instance is also using fe->card->mutex.. so I think double lock may not serve any purpose here..
> >
> >Can you explain why we need the extra lock?
> You are right.
> The mutex_lock with fe->pcm_mutex has no purpose.

Okay

> It just removes lockdep warning like the below
> <4>[ 1437.857354]  [5:          cplay:11547] ------------[ cut here ]------------
> <4>[ 1437.857463]  [5:          cplay:11547] WARNING: CPU: 5 PID: 11547 at sound/soc/soc-pcm.c:99 snd_soc_runtime_deactivate+0x88/0x140
> <4>[ 1437.857498]  [5:          cplay:11547] Modules linked in:
> <4>[ 1437.857557]  [5:          cplay:11547] CPU: 5 PID: 11547 Comm: cplay Tainted: G S      W         4.19.65-00198-ge6c3a8b64f3d-dirty #146
> <4>[ 1437.857590]  [5:          cplay:11547] Hardware name: Samsung xxx board based on xxx (DT)
> <4>[ 1437.857620]  [5:          cplay:11547] Call trace:
> <4>[ 1437.857662]  [5:          cplay:11547] [<ffffff800808d598>] dump_backtrace+0x0/0x404
> <4>[ 1437.857704]  [5:          cplay:11547] [<ffffff800808d9b0>] show_stack+0x14/0x1c
> <4>[ 1437.857745]  [5:          cplay:11547] [<ffffff8008c5dc24>] dump_stack+0xa0/0xd8
> <4>[ 1437.857784]  [5:          cplay:11547] [<ffffff80080a4b28>] __warn+0xcc/0x12c
> <4>[ 1437.857821]  [5:          cplay:11547] [<ffffff8008c5cd78>] report_bug+0x78/0xcc
> <4>[ 1437.857857]  [5:          cplay:11547] [<ffffff800808e5c0>] bug_handler+0x2c/0x88
> <4>[ 1437.857895]  [5:          cplay:11547] [<ffffff8008085510>] brk_handler+0x88/0xc8
> <4>[ 1437.857930]  [5:          cplay:11547] [<ffffff8008080f0c>] do_debug_exception+0x108/0x194
> <4>[ 1437.857968]  [5:          cplay:11547] Exception stack(0xffffff8028b0b960 to 0xffffff8028b0baa0)
> <4>[ 1437.858002]  [5:          cplay:11547] b960: 0000000000000024 ffffff8008e28a97 ffffffc975bb40a0 ffffff8028b0b748
> <4>[ 1437.858035]  [5:          cplay:11547] b980: 0000000000000080 0000000000000000 ffffff8008129638 0000000000000000
> <4>[ 1437.858066]  [5:          cplay:11547] b9a0: e0b1dc92eba18f00 e0b1dc92eba18f00 0000000000000003 0000000000000000
> <4>[ 1437.858098]  [5:          cplay:11547] b9c0: 0000000000240022 0000000000000004 ffffff8009b2f420 00000000fffffff5
> <4>[ 1437.858130]  [5:          cplay:11547] b9e0: ffffff8008c6baac 000000000000002c 00000000000000b0 ffffffc9673c1e80
> <4>[ 1437.858161]  [5:          cplay:11547] ba00: 0000000000000000 ffffffc8190e6100 0000000000000000 ffffffc95c262e88
> <4>[ 1437.858193]  [5:          cplay:11547] ba20: 0000000000000008 ffffffc8ec3050d0 ffffffc8fb81a4d0 0000000000000004
> <4>[ 1437.858224]  [5:          cplay:11547] ba40: 0000000000000009 ffffff8028b0bac0 ffffff8008a895c8 ffffff8028b0baa0
> <4>[ 1437.858256]  [5:          cplay:11547] ba60: ffffff8008a895c8 0000000060400005 ffffff8028b0ba48 ffffff800811d7b4
> <4>[ 1437.858287]  [5:          cplay:11547] ba80: 0000007fffffffff e0b1dc92eba18f00 ffffff8028b0bac0 ffffff8008a895c8
> <4>[ 1437.858318]  [5:          cplay:11547] [<ffffff8008082b18>] el1_dbg+0x18/0x78
> <4>[ 1437.858355]  [5:          cplay:11547] [<ffffff8008a895c8>] snd_soc_runtime_deactivate+0x88/0x140

So if the lockdep is complaining, then we should add lockdep assert in
the open_fe as well..

-- 
~Vinod