linux-kernel - Re: BUG: MAX_STACK_TRACE

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Message-ID: <ee3bac8d-d061-7d07-5990-59871e7e2a4b@gmail.com>
Date:   Wed, 10 Jul 2019 22:47:43 +0200
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Bart Van Assche <bvanassche@....org>,
        Eric Dumazet <eric.dumazet@...il.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>, Will Deacon <will@...nel.org>,
        linux-kernel@...r.kernel.org,
        syzbot <syzbot+6f39a9deb697359fe520@...kaller.appspotmail.com>,
        syzkaller-bugs@...glegroups.com
Subject: Re: BUG: MAX_STACK_TRACE_ENTRIES too low! (2)



On 7/10/19 9:09 PM, Bart Van Assche wrote:
> On 7/10/19 11:44 AM, Eric Dumazet wrote:
>> If anything using workqueues in dynamically allocated objects can turn off lockdep,
>> we have a serious issue.
> 
> As far as I know that issue is only hit by syzbot tests.



> Anyway, I see
> two possible paths forward:
> * Revert the patch that makes workqueues use dynamic lockdep keys and
> thereby reintroduce the false positives that lockdep reports if
> different workqueues share a lockdep key. I think there is agreement
> that having to analyze lockdep false positives is annoying, time
> consuming and something nobody likes.
> * Modify lockdep such that space in its fixed size arrays that is no
> longer in use gets reused. Since the stack traces saved in the
> stack_trace[] array have a variable size that array will have to be
> compacted to avoid fragmentation.
> 

Can not destroy_workqueue() undo what alloc_workqueue() did ?