Re: [PATCH] lockdep: fix fs_reclaim annotation

From: Peter Zijlstra
Date: Fri Apr 20 2018 - 04:18:05 EST

On Sun, Apr 15, 2018 at 12:42:25AM -0700, Omar Sandoval wrote:
> From: Omar Sandoval <osandov@xxxxxx>
> 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:
> Fixes: d92a8cfcb37e ("locking/lockdep: Rework FS_RECLAIM annotation")
> Signed-off-by: Omar Sandoval <osandov@xxxxxx>

Urgh, thanks for fixing that!