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SubjectRe: [PATCH 2/2] fs: xfs: use BUG_ON if writepage call comes from direct reclaim
On Tue, Jul 03, 2018 at 12:11:19PM +0800, Yang Shi wrote:
> direct reclaim doesn't write out filesystem page, only kswapd could do
> this. So, if it is called from direct relaim, it is definitely a bug.
>
> And, Mel Gorman mentioned "Ultimately, this will be a BUG_ON." in commit
> 94054fa3fca1fd78db02cb3d68d5627120f0a1d4 ("xfs: warn if direct reclaim
> tries to writeback pages"),
>
> It has been many years since that commit, so it should be safe to
> elevate WARN_ON to BUG_ON now.
>
> Cc: Mel Gorman <mgorman@techsingularity.net>
> Cc: Darrick J. Wong <darrick.wong@oracle.com>
> Cc: Dave Chinner <dchinner@redhat.com>
> Signed-off-by: Yang Shi <yang.shi@linux.alibaba.com>
> ---
> fs/xfs/xfs_aops.c | 6 ++----
> 1 file changed, 2 insertions(+), 4 deletions(-)
>
> diff --git a/fs/xfs/xfs_aops.c b/fs/xfs/xfs_aops.c
> index 8eb3ba3..7efc2d2 100644
> --- a/fs/xfs/xfs_aops.c
> +++ b/fs/xfs/xfs_aops.c
> @@ -1080,11 +1080,9 @@ static inline int xfs_bio_add_buffer(struct bio *bio, struct buffer_head *bh)
> * allow reclaim from kswapd as the stack usage there is relatively low.
> *
> * This should never happen except in the case of a VM regression so
> - * warn about it.
> + * BUG about it.
> */
> - if (WARN_ON_ONCE((current->flags & (PF_MEMALLOC|PF_KSWAPD)) ==
> - PF_MEMALLOC))
> - goto redirty;
> + BUG_ON((current->flags & (PF_MEMALLOC|PF_KSWAPD)) == PF_MEMALLOC);

Ugh, please do not increase the BUG() factor. Even if this happens due
to a regression it's /much/ easier to debug if we don't halt the system.

(IOWs, I decline to take this patch.)

--D

>
> /*
> * Given that we do not allow direct reclaim to call us, we should
> --
> 1.8.3.1
>
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