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From: Eric Biggers <ebiggers@kernel.org>
To: linux-xfs@vger.kernel.org
Cc: linux-ext4@vger.kernel.org, syzkaller-bugs@googlegroups.com,
	linux-kernel@vger.kernel.org
Subject: [PATCH] xfs: clear PF_MEMALLOC before exiting xfsaild thread
Date: Sat,  7 Mar 2020 20:35:40 -0800	[thread overview]
Message-ID: <20200308043540.1034779-1-ebiggers@kernel.org> (raw)
In-Reply-To: <0000000000000e7156059f751d7b@google.com>

From: Eric Biggers <ebiggers@google.com>

Leaving PF_MEMALLOC set when exiting a kthread causes it to remain set
during do_exit().  That can confuse things.  For example, if BSD process
accounting is enabled, then it's possible for do_exit() to end up
calling ext4_write_inode().  That triggers the
WARN_ON_ONCE(current->flags & PF_MEMALLOC) there, as it assumes
(appropriately) that inodes aren't written when allocating memory.

This case was reported by syzbot at
https://lkml.kernel.org/r/0000000000000e7156059f751d7b@google.com.

Fix this in xfsaild() by using the helper functions to save and restore
PF_MEMALLOC.

Reported-by: syzbot+1f9dc49e8de2582d90c2@syzkaller.appspotmail.com
Signed-off-by: Eric Biggers <ebiggers@google.com>
---
 fs/xfs/xfs_trans_ail.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/fs/xfs/xfs_trans_ail.c b/fs/xfs/xfs_trans_ail.c
index 00cc5b8734be..3bc570c90ad9 100644
--- a/fs/xfs/xfs_trans_ail.c
+++ b/fs/xfs/xfs_trans_ail.c
@@ -529,8 +529,9 @@ xfsaild(
 {
 	struct xfs_ail	*ailp = data;
 	long		tout = 0;	/* milliseconds */
+	unsigned int	noreclaim_flag;
 
-	current->flags |= PF_MEMALLOC;
+	noreclaim_flag = memalloc_noreclaim_save();
 	set_freezable();
 
 	while (1) {
@@ -601,6 +602,7 @@ xfsaild(
 		tout = xfsaild_push(ailp);
 	}
 
+	memalloc_noreclaim_restore(noreclaim_flag);
 	return 0;
 }
 
-- 
2.25.1


  reply	other threads:[~2020-03-08  4:36 UTC|newest]

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-02-26  6:57 WARNING in ext4_write_inode syzbot
2020-03-08  4:35 ` Eric Biggers [this message]
2020-03-08 23:03   ` [PATCH] xfs: clear PF_MEMALLOC before exiting xfsaild thread Dave Chinner
2020-03-09  1:04     ` Eric Biggers
2020-03-09  4:34       ` [PATCH v2] " Eric Biggers
2020-03-09 10:57         ` Brian Foster
2020-03-09 16:24         ` Darrick J. Wong
2020-03-09 18:04           ` Eric Biggers
2020-03-09 18:13             ` Darrick J. Wong
2020-03-09 18:57               ` [PATCH v3] " Eric Biggers
2020-03-10 15:47                 ` Darrick J. Wong
2020-03-11  6:34                 ` Christoph Hellwig
2020-03-12 22:20           ` [PATCH v2] " Eric Biggers
2020-03-08  4:36 ` [PATCH] cifs: clear PF_MEMALLOC before exiting demultiplex thread Eric Biggers
2020-03-08  6:16   ` [PATCH v2] " Eric Biggers
2020-03-08 18:43     ` Steve French
2020-03-09  5:56       ` Eric Biggers
2020-03-09  5:58         ` [PATCH v3] " Eric Biggers

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