linux-kernel - Re: [syzbot] WARNING: locking bug in umh

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Message-ID: <Y/Xhsna3gfadzAAk@hirez.programming.kicks-ass.net>
Date:   Wed, 22 Feb 2023 10:34:42 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Schspa Shi <schspa@...il.com>
Cc:     Luis Chamberlain <mcgrof@...nel.org>,
        Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
        Ingo Molnar <mingo@...nel.org>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        linux-kernel@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        syzkaller-bugs@...glegroups.com,
        syzbot <syzbot+6cd18e123583550cf469@...kaller.appspotmail.com>,
        Hillf Danton <hdanton@...a.com>
Subject: Re: [syzbot] WARNING: locking bug in umh_complete

On Tue, Feb 14, 2023 at 10:31:58AM +0800, Schspa Shi wrote:
> Peter Zijlstra <peterz@...radead.org> writes:

> > If so, perhaps the simplest rule would to be ensure there is an
> > unconditional uninterruptible wait-for-completion() before going out of
> > scope.
> >
> > This latter can be spelled like wait_for_completion() or
> > wait_for_completion_state(TASK_UNINTERRUPTIBLE). More specifically,
> > TASK_INTERRUPTIBLE and TASK_WAKEKILL must not be set in the state mask
> > for the wait to be uninterruptible.
> >
> > If it cannot be proven, raise a warning and audit or somesuch.
> 
> This is a good suggestion. I have written a SmPL patch to complete this
> check, and now I need to rule out the situation that the driver has
> added an additional lock to protect it.
> 
> And I have found a lot of bad usage, should we consider adding a new
> helper API to simplify the fix this?

Please first share some of the locations where this would be applied.