linux-kernel - Re: BUG: MAX_STACK_TRACE

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Date:   Wed, 10 Jul 2019 10:46:00 -0700
From:   Bart Van Assche <bvanassche@....org>
To:     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 10:21 AM, Eric Biggers wrote:
> With my simplified reproducer, on commit 669de8bda87b ("kernel/workqueue: Use
> dynamic lockdep keys for workqueues") I see:
> 
> 	WARNING: CPU: 3 PID: 189 at kernel/locking/lockdep.c:747 register_lock_class+0x4f6/0x580
> 
> and then somewhat later:
> 
> 	BUG: MAX_LOCKDEP_KEYS too low!
> 
> If on top of that I cherry pick commit 28d49e282665 ("locking/lockdep: Shrink
> struct lock_class_key"), I see instead:
> 
> 	BUG: MAX_STACK_TRACE_ENTRIES too low!
> 
> I also see that on mainline.
> 
> Alternatively, if I check out 669de8bda87b and revert it, I don't see anything.

Hi Eric,

Is the rdma_ucm code the only code that triggers the "BUG:
MAX_STACK_TRACE_ENTRIES too low!" complaint or is this complaint also
triggered by other kernel code? I'm asking this because I think that
fixing this would require to implement garbage collection for the
stack_trace[] array in the lockdep code. That would make the lockdep
code slower. I don't think that making the lockdep code slower would be
welcome.

Bart.