linux-kernel - Re: [PATCH v1 3/3] PM: sleep: Fix possible deadlocks in core system-wide PM code

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Message-ID: <2024010322-uneven-nanometer-7d6d@gregkh>
Date: Wed, 3 Jan 2024 11:33:58 +0100
From: Greg KH <gregkh@...uxfoundation.org>
To: Ulf Hansson <ulf.hansson@...aro.org>
Cc: "Rafael J. Wysocki" <rafael@...nel.org>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>, linux-pm@...r.kernel.org,
	Youngmin Nam <youngmin.nam@...sung.com>,
	linux-kernel@...r.kernel.org, d7271.choe@...sung.com,
	janghyuck.kim@...sung.com, hyesoo.yu@...sung.com,
	Alan Stern <stern@...land.harvard.edu>
Subject: Re: [PATCH v1 3/3] PM: sleep: Fix possible deadlocks in core
 system-wide PM code

On Wed, Jan 03, 2024 at 11:17:18AM +0100, Ulf Hansson wrote:
> On Tue, 2 Jan 2024 at 14:54, Rafael J. Wysocki <rafael@...nel.org> wrote:
> >
> > On Tue, Jan 2, 2024 at 2:35 PM Ulf Hansson <ulf.hansson@...aro.org> wrote:
> > >
> > > On Wed, 27 Dec 2023 at 21:41, Rafael J. Wysocki <rjw@...ysocki.net> wrote:
> > > >
> > > > From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> > > >
> > > > It is reported that in low-memory situations the system-wide resume core
> > > > code deadlocks, because async_schedule_dev() executes its argument
> > > > function synchronously if it cannot allocate memory (an not only then)
> > > > and that function attempts to acquire a mutex that is already held.
> > > >
> > > > Address this by changing the code in question to use
> > > > async_schedule_dev_nocall() for scheduling the asynchronous
> > > > execution of device suspend and resume functions and to directly
> > > > run them synchronously if async_schedule_dev_nocall() returns false.
> > > >
> > > > Fixes: 09beebd8f93b ("PM: sleep: core: Switch back to async_schedule_dev()")
> > > > Link: https://lore.kernel.org/linux-pm/ZYvjiqX6EsL15moe@perf/
> > > > Reported-by: Youngmin Nam <youngmin.nam@...sung.com>
> > > > Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> > > > ---
> > > >
> > > > The commit pointed to by the Fixes: tag is the last one that modified
> > > > the code in question, even though the bug had been there already before.
> > > >
> > > > Still, the fix will not apply to the code before that commit.
> > >
> > > An option could be to just do "Cc: stable@...r.kernel.org # v5.7+"
> > > instead of pointing to a commit with a Fixes tag.
> >
> > Right, but one can argue that every commit with a "Cc: stable" tag is
> > a fix, so it should carry a Fixes: tag too anyway.
> 
> Yes, certainly. But in this case it's more questionable as it's not
> really fixing the commit it points out.
> 
> Note that, I have no strong opinion here, but maybe Greg has a preferred way?

Either is fine with me, just to give me a good hint on how far back a
commit should be backported to.

thanks,

greg k-h