linux-kernel - Re: [PATCH] lockdep: fix fs

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Date:   Tue, 24 Apr 2018 15:58:34 -0700
From:   Omar Sandoval <osandov@...ndov.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-kernel@...r.kernel.org,
        Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
        Ingo Molnar <mingo@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        kernel-team@...com
Subject: Re: [PATCH] lockdep: fix fs_reclaim annotation

On Fri, Apr 20, 2018 at 10:17:42AM +0200, Peter Zijlstra wrote:
> On Sun, Apr 15, 2018 at 12:42:25AM -0700, Omar Sandoval wrote:
> > From: Omar Sandoval <osandov@...com>
> > 
> > While revisiting my Btrfs swapfile series [1], I introduced a situation
> > in which reclaim would lock i_rwsem, and even though the swapon() path
> > clearly made GFP_KERNEL allocations while holding i_rwsem, I got no
> > complaints from lockdep. It turns out that the rework of the fs_reclaim
> > annotation was broken: if the current task has PF_MEMALLOC set, we don't
> > acquire the dummy fs_reclaim lock, but when reclaiming we always check
> > this _after_ we've just set the PF_MEMALLOC flag. In most cases, we can
> > fix this by moving the fs_reclaim_{acquire,release}() outside of the
> > memalloc_noreclaim_{save,restore}(), althought kswapd is slightly
> > different. After applying this, I got the expected lockdep splats.
> > 
> > 1: https://lwn.net/Articles/625412/
> > Fixes: d92a8cfcb37e ("locking/lockdep: Rework FS_RECLAIM annotation")
> > Signed-off-by: Omar Sandoval <osandov@...com>
> 
> Urgh, thanks for fixing that!

Is this going to go through the tip tree? Should Andrew take it?