Re: [PATCH -mm 0/2] Use freezeable workqueues to avoid suspend-related XFS corruptions

[Nigel Cunningham <nigel@suspend2.net>]

Hi all.

I've did some testing this afternoon with bdev freezing disabled and
without any non-vanilla code to freeze kthreads (Rafael's or my older
version).

If I put a BUG_ON() in submit_bio for non suspend2 I/O, it catches this
trace:

submit_bio
xfs_buf_iorequest
xlog_bdstrat_cb
xlog_state_release_iclog
xlog_state_sync_all
xfs_log_force
xfs_syncsub
xfs_sync
vfs_sync
vfs_sync_worker
xfssyncd
keventd_create_kthread

I haven't yet reproduced anything on another code path (eg pdflush).

So, it would appear that freezing kthreads without freezing bdevs should
be a possible solution. It may however leave some I/O unsynced
pre-resume and therefore result in possible dataloss if no resume
occurs. I therefore wonder whether it's better to stick with bdev
freezing or create some variant wherein XFS is taught to fully flush
pending writes and not create new I/O.

Regards,

Nigel