From: Tzung-Bi Shih <tzungbi@google.com>
To: Marek Szyprowski <m.szyprowski@samsung.com>
Cc: ALSA development <alsa-devel@alsa-project.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Linux Samsung SOC <linux-samsung-soc@vger.kernel.org>,
Mark Brown <broonie@kernel.org>,
Sylwester Nawrocki <s.nawrocki@samsung.com>,
Dylan Reid <dgreid@google.com>,
Jimmy Cheng-Yi Chiang <cychiang@google.com>,
Krzysztof Kozlowski <krzk@kernel.org>,
Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Subject: Re: [PATCH 2/2] ASoC: max98090: fix lockdep warning
Date: Fri, 10 Jan 2020 09:05:59 +0800 [thread overview]
Message-ID: <CA+Px+wWiZ9MWwi-moXo9rJrbgLFVEbOqjQMhOZmm5mRL7EeMbQ@mail.gmail.com> (raw)
In-Reply-To: <83169752-ac05-d1b1-ece9-fbe1109287cf@samsung.com>
On Thu, Jan 9, 2020 at 7:09 PM Marek Szyprowski
<m.szyprowski@samsung.com> wrote:
> On 09.01.2020 06:36, Tzung-Bi Shih wrote:
> > On Wed, Jan 8, 2020 at 7:50 PM Marek Szyprowski
> > <m.szyprowski@samsung.com> wrote:
> >> Fix this by introducing a separate mutex only for serializing the SHDN
> >> hardware register related operations.
> > This fix makes less sense to me. We used dapm_mutex intentionally
> > because: both DAPM and userspace mixer control would change SHDN bit
> > at the same time.
We should not use a separate lock. Either mixer control or DAPM would
change the SHDN bit. The patch overlooks the calling path from DAPM.
As a result, DAPM can change the bit in the middle of mixer control.
> Nope. This is just a lockdep warning about possible hypothetical
> situation on the test system during the normal boot. It doesn't mean
> that the circular dependency actually happens (if so, it would end in
> deadlock). It also doesn't mean that such circular dependency can be
> really triggered, because some other dependencies that not known to
> lockdep engine might protect against it. However the easiest way to fix
> it is to use fine-grained locking instead of reusing some framework
> locks for other purposes. Such approach is also usually a good practice.
If the possible circular locking is a hypothetical situation, shall we
ignore it since we are very sure userspace cannot see the control
devices when building the sound card?
WARNING: multiple messages have this Message-ID (diff)
From: Tzung-Bi Shih <tzungbi@google.com>
To: Marek Szyprowski <m.szyprowski@samsung.com>
Cc: ALSA development <alsa-devel@alsa-project.org>,
Linux Samsung SOC <linux-samsung-soc@vger.kernel.org>,
Jimmy Cheng-Yi Chiang <cychiang@google.com>,
Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Krzysztof Kozlowski <krzk@kernel.org>,
Mark Brown <broonie@kernel.org>,
Sylwester Nawrocki <s.nawrocki@samsung.com>,
Dylan Reid <dgreid@google.com>
Subject: Re: [alsa-devel] [PATCH 2/2] ASoC: max98090: fix lockdep warning
Date: Fri, 10 Jan 2020 09:05:59 +0800 [thread overview]
Message-ID: <CA+Px+wWiZ9MWwi-moXo9rJrbgLFVEbOqjQMhOZmm5mRL7EeMbQ@mail.gmail.com> (raw)
In-Reply-To: <83169752-ac05-d1b1-ece9-fbe1109287cf@samsung.com>
On Thu, Jan 9, 2020 at 7:09 PM Marek Szyprowski
<m.szyprowski@samsung.com> wrote:
> On 09.01.2020 06:36, Tzung-Bi Shih wrote:
> > On Wed, Jan 8, 2020 at 7:50 PM Marek Szyprowski
> > <m.szyprowski@samsung.com> wrote:
> >> Fix this by introducing a separate mutex only for serializing the SHDN
> >> hardware register related operations.
> > This fix makes less sense to me. We used dapm_mutex intentionally
> > because: both DAPM and userspace mixer control would change SHDN bit
> > at the same time.
We should not use a separate lock. Either mixer control or DAPM would
change the SHDN bit. The patch overlooks the calling path from DAPM.
As a result, DAPM can change the bit in the middle of mixer control.
> Nope. This is just a lockdep warning about possible hypothetical
> situation on the test system during the normal boot. It doesn't mean
> that the circular dependency actually happens (if so, it would end in
> deadlock). It also doesn't mean that such circular dependency can be
> really triggered, because some other dependencies that not known to
> lockdep engine might protect against it. However the easiest way to fix
> it is to use fine-grained locking instead of reusing some framework
> locks for other purposes. Such approach is also usually a good practice.
If the possible circular locking is a hypothetical situation, shall we
ignore it since we are very sure userspace cannot see the control
devices when building the sound card?
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next prev parent reply other threads:[~2020-01-10 1:06 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <CGME20200108115027eucas1p2abcd40e359e993e5b471229b02b69fc3@eucas1p2.samsung.com>
2020-01-08 11:50 ` [PATCH 1/2] ASoC: max98090: fix incorrect helper in max98090_dapm_put_enum_double() Marek Szyprowski
2020-01-08 11:50 ` [alsa-devel] " Marek Szyprowski
[not found] ` <CGME20200108115027eucas1p1d3645ba53703780679c662921efbca78@eucas1p1.samsung.com>
2020-01-08 11:50 ` [PATCH 2/2] ASoC: max98090: fix lockdep warning Marek Szyprowski
2020-01-08 11:50 ` [alsa-devel] " Marek Szyprowski
2020-01-09 5:36 ` Tzung-Bi Shih
2020-01-09 5:36 ` [alsa-devel] " Tzung-Bi Shih
2020-01-09 10:59 ` Tzung-Bi Shih
2020-01-09 10:59 ` [alsa-devel] " Tzung-Bi Shih
2020-01-09 11:09 ` Marek Szyprowski
2020-01-09 11:09 ` [alsa-devel] " Marek Szyprowski
2020-01-10 1:05 ` Tzung-Bi Shih [this message]
2020-01-10 1:05 ` Tzung-Bi Shih
2020-01-09 21:29 ` Applied "ASoC: max98090: fix lockdep warning" to the asoc tree Mark Brown
2020-01-09 21:29 ` [alsa-devel] " Mark Brown
2020-01-09 5:11 ` [PATCH 1/2] ASoC: max98090: fix incorrect helper in max98090_dapm_put_enum_double() Tzung-Bi Shih
2020-01-09 5:11 ` [alsa-devel] " Tzung-Bi Shih
2020-01-09 21:29 ` Applied "ASoC: max98090: fix incorrect helper in max98090_dapm_put_enum_double()" to the asoc tree Mark Brown
2020-01-09 21:29 ` [alsa-devel] " Mark Brown
2020-01-09 21:29 ` Mark Brown
2020-01-09 21:29 ` [alsa-devel] " Mark Brown
2020-01-10 9:02 ` Marek Szyprowski
2020-01-10 9:02 ` [alsa-devel] " Marek Szyprowski
2020-01-10 13:25 ` Mark Brown
2020-01-10 13:25 ` [alsa-devel] " Mark Brown
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