From: Eric Biggers <ebiggers@xxxxxxxxxx> 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 and the accounting file has FS_SYNC_FL set and is located on an ext4 filesystem without a journal, then do_exit() ends 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. Fix this in xfsaild() by using the helper functions to save and restore PF_MEMALLOC. This can be reproduced as follows in the kvm-xfstests test appliance modified to add the 'acct' Debian package, and with kvm-xfstests's recommended kconfig modified to add CONFIG_BSD_PROCESS_ACCT=y: mkfs.ext2 -F /dev/vdb mount /vdb -t ext4 touch /vdb/file chattr +S /vdb/file accton /vdb/file mkfs.xfs -f /dev/vdc mount /vdc umount /vdc It causes: WARNING: CPU: 0 PID: 332 at fs/ext4/inode.c:5097 ext4_write_inode+0x140/0x1a0 CPU: 0 PID: 332 Comm: xfsaild/vdc Not tainted 5.6.0-rc5 #5 [...] RIP: 0010:ext4_write_inode+0x140/0x1a0 fs/ext4/inode.c:5097 [...] Call Trace: write_inode fs/fs-writeback.c:1312 [inline] __writeback_single_inode+0x465/0x5f0 fs/fs-writeback.c:1511 writeback_single_inode+0xad/0x120 fs/fs-writeback.c:1565 sync_inode fs/fs-writeback.c:2602 [inline] sync_inode_metadata+0x3d/0x57 fs/fs-writeback.c:2622 ext4_fsync_nojournal fs/ext4/fsync.c:94 [inline] ext4_sync_file+0x243/0x4b0 fs/ext4/fsync.c:172 generic_write_sync include/linux/fs.h:2867 [inline] ext4_buffered_write_iter+0xe1/0x130 fs/ext4/file.c:277 call_write_iter include/linux/fs.h:1901 [inline] new_sync_write+0x130/0x1d0 fs/read_write.c:483 __kernel_write+0x54/0xe0 fs/read_write.c:515 do_acct_process+0x122/0x170 kernel/acct.c:522 slow_acct_process kernel/acct.c:581 [inline] acct_process+0x1d4/0x27c kernel/acct.c:607 do_exit+0x83d/0xbc0 kernel/exit.c:791 kthread+0xf1/0x140 kernel/kthread.c:257 ret_from_fork+0x27/0x50 arch/x86/entry/entry_64.S:352 This case was originally reported by syzbot at https://lore.kernel.org/r/0000000000000e7156059f751d7b@xxxxxxxxxx. Reported-by: syzbot+1f9dc49e8de2582d90c2@xxxxxxxxxxxxxxxxxxxxxxxxx Signed-off-by: Eric Biggers <ebiggers@xxxxxxxxxx> --- v2: include more details in the commit message. 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 00cc5b8734be8..3bc570c90ad97 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
