linux-kernel - [PATCH] xfs: clear PF_MEMALLOC before exiting xfsaild thread

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Message-Id: <20200308043540.1034779-1-ebiggers@kernel.org>
Date:   Sat,  7 Mar 2020 20:35:40 -0800
From:   Eric Biggers <ebiggers@...nel.org>
To:     linux-xfs@...r.kernel.org
Cc:     linux-ext4@...r.kernel.org, syzkaller-bugs@...glegroups.com,
        linux-kernel@...r.kernel.org
Subject: [PATCH] xfs: clear PF_MEMALLOC before exiting xfsaild thread

From: Eric Biggers <ebiggers@...gle.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@...kaller.appspotmail.com
Signed-off-by: Eric Biggers <ebiggers@...gle.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