From: "Darrick J. Wong" djwong@kernel.org
[ Upstream commit f0c2d7d2abca24d19831c99edea458704fac8087 ]
Every now and then, I see the following hang during mount time quotacheck when running fstests. Turning on KASAN seems to make it happen somewhat more frequently. I've edited the backtrace for brevity.
XFS (sdd): Quotacheck needed: Please wait. XFS: Assertion failed: bp->b_flags & _XBF_DELWRI_Q, file: fs/xfs/xfs_buf.c, line: 2411 ------------[ cut here ]------------ WARNING: CPU: 0 PID: 1831409 at fs/xfs/xfs_message.c:104 assfail+0x46/0x4a [xfs] CPU: 0 PID: 1831409 Comm: mount Tainted: G W 5.19.0-rc6-xfsx #rc6 09911566947b9f737b036b4af85e399e4b9aef64 Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.15.0-1 04/01/2014 RIP: 0010:assfail+0x46/0x4a [xfs] Code: a0 8f 41 a0 e8 45 fe ff ff 8a 1d 2c 36 10 00 80 fb 01 76 0f 0f b6 f3 48 c7 c7 c0 f0 4f a0 e8 10 f0 02 e1 80 e3 01 74 02 0f 0b <0f> 0b 5b c3 48 8d 45 10 48 89 e2 4c 89 e6 48 89 1c 24 48 89 44 24 RSP: 0018:ffffc900078c7b30 EFLAGS: 00010246 RAX: 0000000000000000 RBX: ffff8880099ac000 RCX: 000000007fffffff RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffffffffa0418fa0 RBP: ffff8880197bc1c0 R08: 0000000000000000 R09: 000000000000000a R10: 000000000000000a R11: f000000000000000 R12: ffffc900078c7d20 R13: 00000000fffffff5 R14: ffffc900078c7d20 R15: 0000000000000000 FS: 00007f0449903800(0000) GS:ffff88803ec00000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00005610ada631f0 CR3: 0000000014dd8002 CR4: 00000000001706f0 Call Trace: <TASK> xfs_buf_delwri_pushbuf+0x150/0x160 [xfs 4561f5b32c9bfb874ec98d58d0719464e1f87368] xfs_qm_flush_one+0xd6/0x130 [xfs 4561f5b32c9bfb874ec98d58d0719464e1f87368] xfs_qm_dquot_walk.isra.0+0x109/0x1e0 [xfs 4561f5b32c9bfb874ec98d58d0719464e1f87368] xfs_qm_quotacheck+0x319/0x490 [xfs 4561f5b32c9bfb874ec98d58d0719464e1f87368] xfs_qm_mount_quotas+0x65/0x2c0 [xfs 4561f5b32c9bfb874ec98d58d0719464e1f87368] xfs_mountfs+0x6b5/0xab0 [xfs 4561f5b32c9bfb874ec98d58d0719464e1f87368] xfs_fs_fill_super+0x781/0x990 [xfs 4561f5b32c9bfb874ec98d58d0719464e1f87368] get_tree_bdev+0x175/0x280 vfs_get_tree+0x1a/0x80 path_mount+0x6f5/0xaa0 __x64_sys_mount+0x103/0x140 do_syscall_64+0x2b/0x80 entry_SYSCALL_64_after_hwframe+0x46/0xb0
I /think/ this can happen if xfs_qm_flush_one is racing with xfs_qm_dquot_isolate (i.e. dquot reclaim) when the second function has taken the dquot flush lock but xfs_qm_dqflush hasn't yet locked the dquot buffer, let alone queued it to the delwri list. In this case, flush_one will fail to get the dquot flush lock, but it can lock the incore buffer, but xfs_buf_delwri_pushbuf will then trip over this ASSERT, which checks that the buffer isn't on a delwri list. The hang results because the _delwri_submit_buffers ignores non DELWRI_Q buffers, which means that xfs_buf_iowait waits forever for an IO that has not yet been scheduled.
AFAICT, a reasonable solution here is to detect a dquot buffer that is not on a DELWRI list, drop it, and return -EAGAIN to try the flush again. It's not /that/ big of a deal if quotacheck writes the dquot buffer repeatedly before we even set QUOTA_CHKD.
Signed-off-by: Darrick J. Wong djwong@kernel.org Reviewed-by: Dave Chinner dchinner@redhat.com Signed-off-by: Alexey Panov apanov@astralinux.ru --- Tested with the syzkaller reproducer for https://syzkaller.appspot.com/bug?extid=3ae67535b07c92aa02fd: the issue triggers on vanilla v5.10.y and no longer reproduces with this patch applied. fs/xfs/xfs_qm.c | 7 +++++++ 1 file changed, 7 insertions(+)
diff --git a/fs/xfs/xfs_qm.c b/fs/xfs/xfs_qm.c index 3c17e0c0f816..907819e7873e 100644 --- a/fs/xfs/xfs_qm.c +++ b/fs/xfs/xfs_qm.c @@ -1245,6 +1245,13 @@ xfs_qm_flush_one( error = -EINVAL; goto out_unlock; } + + if (!(bp->b_flags & _XBF_DELWRI_Q)) { + error = -EAGAIN; + xfs_buf_relse(bp); + goto out_unlock; + } + xfs_buf_unlock(bp);
xfs_buf_delwri_pushbuf(bp, buffer_list);