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

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Date:   Mon, 26 Oct 2020 12:55:41 +0100
From:   Jan Kara <jack@...e.cz>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Filipe Manana <fdmanana@...e.com>,
        LKML <linux-kernel@...r.kernel.org>, Jan Kara <jack@...e.cz>,
        David Sterba <dsterba@...e.com>
Subject: Re: possible lockdep regression introduced by 4d004099a668
 ("lockdep: Fix lockdep recursion")

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@...radead.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?

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...

								Honza
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR