在 2023/6/27 5:45, Dave Chinner 写道:
On Mon, Jun 26, 2023 at 09:15:42PM +0800, yangerkun wrote:
From: yangerkun <yangerkun@xxxxxxxxxx>
Combine use of xfs_trans_hold and xfs_trans_set_sync in xfs_sync_sb_buf
can trigger a deadlock once shutdown happened concurrently. xlog_ioend_work
will first unpin the sb(which stuck with xfs_buf_lock), then wakeup
xfs_sync_sb_buf. However, xfs_sync_sb_buf never get the chance to unlock
sb until been wakeup by xlog_ioend_work.
xfs_sync_sb_buf
xfs_trans_getsb // lock sb buf
xfs_trans_bhold // sb buf keep lock until success commit
xfs_trans_commit
...
xfs_log_force_seq
xlog_force_lsn
xlog_wait_on_iclog
xlog_wait(&iclog->ic_force_wait... // shutdown happened
xfs_buf_relse // unlock sb buf
xlog_ioend_work
xlog_force_shutdown
xlog_state_shutdown_callbacks
xlog_cil_process_committed
xlog_cil_committed
...
xfs_buf_item_unpin
xfs_buf_lock // deadlock
wake_up_all(&iclog->ic_force_wait)
xfs_ioc_setlabel use xfs_sync_sb_buf to make sure userspace will see the
change for sb immediately. We can simply call xfs_ail_push_all_sync to
do this and sametime fix the deadlock.
Why is this deadlock specific to the superblock buffer?
Hi Dave,
Thanks a lot for your revirew! We find this problem when do some code
reading(which can help us to fix another growfs bug). And then reproduce
it easily when we set label online frequently with IO error inject at
the sametime.
Can't any buffer that is held locked over a synchronous transaction
commit deadlock during a shutdown like this?
After check all place use xfs_buf_bhold, it seems xfs_sync_sb_buf is the
only convict that combine use xfs_trans_hold and xfs_trans_set_sync(I'm
not familiar with xfs yet, so I may have some problems with my code
check)...
Thanks,
Yang Erkun.
Cheers,
Dave.
