Re: possible lockdep regression introduced by 4d004099a668 ("lockdep: Fix lockdep recursion")

[Filipe Manana <fdmanana@suse.com>]

On 26/10/20 11:40, Peter Zijlstra wrote:
> On Mon, Oct 26, 2020 at 11:26:49AM +0000, Filipe Manana wrote:
>> Hello,
>>
>> I've recently started to hit a warning followed by tasks hanging after
>> attempts to freeze a filesystem. A git bisection pointed to the
>> following commit:
>>
>> commit 4d004099a668c41522242aa146a38cc4eb59cb1e
>> Author: Peter Zijlstra <peterz@infradead.org>
>> Date:   Fri Oct 2 11:04:21 2020 +0200
>>
>>     lockdep: Fix lockdep recursion
>>
>> This happens very reliably when running all xfstests with lockdep
>> enabled, and the tested filesystem is btrfs (haven't tried other
>> filesystems, but it shouldn't matter). The warning and task hangs always
>> happen at either test generic/068 or test generic/390, and (oddly)
>> always have to run all tests for it to trigger, running those tests
>> individually on an infinite loop doesn't seem to trigger it (at least
>> for a couple hours).
>>
>> The warning triggered is at fs/super.c:__sb_start_write() which always
>> results later in several tasks hanging on a percpu rw_sem:
>>
>> https://pastebin.com/qnLvf94E
>>
>> What happens is percpu_rwsem_is_held() is apparently returning a false
>> positive,
> 
> That smells like the same issue reported here:
> 
>   https://lkml.kernel.org/r/20201022111700.GZ2651@hirez.programming.kicks-ass.net
> 
> Make sure you have commit:
> 
>   f8e48a3dca06 ("lockdep: Fix preemption WARN for spurious IRQ-enable")
> 
> (in Linus' tree by now) and do you have CONFIG_DEBUG_PREEMPT enabled?

Yes, CONFIG_DEBUG_PREEMPT is enabled.
I'll try with that commit and let you know, however it's gonna take a
few hours to build a kernel and run all fstests (on that test box it
takes over 3 hours) to confirm that fixes the issue.

Thanks for the quick reply!

> 
> 
> 
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