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

[Filipe Manana]

On 26/10/20 11:55, Jan Kara wrote:
> On Mon 26-10-20 12:40:09, 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@xxxxxxxxxxxxx>
>>> 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@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
>>
>> 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?
> 
> Hum, I am at 5.10-rc1 now and above mentioned commit doesn't appear to be
> there? Also googling for the title doesn't help...

Same here, can't find in Linus' tree neither through google.

> 
> 								Honza
>