linux-ext4 - [PATCH 2/2] fs: xfs: use BUG_ON if writepage call comes from direct reclaim

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Date:   Tue,  3 Jul 2018 12:11:19 +0800
From:   Yang Shi <yang.shi@...ux.alibaba.com>
To:     mgorman@...hsingularity.net, tytso@....edu,
        adilger.kernel@...ger.ca, darrick.wong@...cle.com,
        dchinner@...hat.com, akpm@...ux-foundation.org
Cc:     yang.shi@...ux.alibaba.com, linux-ext4@...r.kernel.org,
        linux-xfs@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: [PATCH 2/2] fs: xfs: use BUG_ON if writepage call comes from direct reclaim

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@...hsingularity.net>
Cc: Darrick J. Wong <darrick.wong@...cle.com>
Cc: Dave Chinner <dchinner@...hat.com>
Signed-off-by: Yang Shi <yang.shi@...ux.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);
 
 	/*
 	 * Given that we do not allow direct reclaim to call us, we should
-- 
1.8.3.1