From: Eric Biggers ebiggers@google.com
commit 10a98cb16d80be3595fdb165fad898bb28b8b6d2 upstream.
Leaving PF_MEMALLOC set when exiting a kthread causes it to remain set during do_exit(). That can confuse things. In particular, if BSD process accounting is enabled, then do_exit() writes data to an accounting file. If that file has FS_SYNC_FL set, then this write occurs synchronously and can misbehave if PF_MEMALLOC is set.
For example, if the accounting file is located on an XFS filesystem, then a WARN_ON_ONCE() in iomap_do_writepage() is triggered and the data doesn't get written when it should. Or if the accounting file is located on an ext4 filesystem without a journal, then a WARN_ON_ONCE() in ext4_write_inode() is triggered and the inode doesn't get written.
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.xfs -f /dev/vdb mount /vdb touch /vdb/file chattr +S /vdb/file accton /vdb/file mkfs.xfs -f /dev/vdc mount /vdc umount /vdc
It causes: WARNING: CPU: 1 PID: 336 at fs/iomap/buffered-io.c:1534 CPU: 1 PID: 336 Comm: xfsaild/vdc Not tainted 5.6.0-rc5 #3 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS ?-20191223_100556-anatol 04/01/2014 RIP: 0010:iomap_do_writepage+0x16b/0x1f0 fs/iomap/buffered-io.c:1534 [...] Call Trace: write_cache_pages+0x189/0x4d0 mm/page-writeback.c:2238 iomap_writepages+0x1c/0x33 fs/iomap/buffered-io.c:1642 xfs_vm_writepages+0x65/0x90 fs/xfs/xfs_aops.c:578 do_writepages+0x41/0xe0 mm/page-writeback.c:2344 __filemap_fdatawrite_range+0xd2/0x120 mm/filemap.c:421 file_write_and_wait_range+0x71/0xc0 mm/filemap.c:760 xfs_file_fsync+0x7a/0x2b0 fs/xfs/xfs_file.c:114 generic_write_sync include/linux/fs.h:2867 [inline] xfs_file_buffered_aio_write+0x379/0x3b0 fs/xfs/xfs_file.c:691 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 bug was originally reported by syzbot at https://lore.kernel.org/r/0000000000000e7156059f751d7b@google.com.
Reported-by: syzbot+1f9dc49e8de2582d90c2@syzkaller.appspotmail.com Signed-off-by: Eric Biggers ebiggers@google.com Reviewed-by: Darrick J. Wong darrick.wong@oracle.com Signed-off-by: Darrick J. Wong darrick.wong@oracle.com Reviewed-by: Christoph Hellwig hch@lst.de Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- fs/xfs/xfs_trans_ail.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-)
--- a/fs/xfs/xfs_trans_ail.c +++ b/fs/xfs/xfs_trans_ail.c @@ -520,8 +520,9 @@ 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) { @@ -592,6 +593,7 @@ xfsaild( tout = xfsaild_push(ailp); }
+ memalloc_noreclaim_restore(noreclaim_flag); return 0; }