Re: [PATCH v2] xfs: fix iclog release error check race with shutdown

[Christoph Hellwig <hch@infradead.org>]

On Tue, Feb 18, 2020 at 12:54:25PM -0500, Brian Foster wrote:
> Prior to commit df732b29c8 ("xfs: call xlog_state_release_iclog with
> l_icloglock held"), xlog_state_release_iclog() always performed a
> locked check of the iclog error state before proceeding into the
> sync state processing code. As of this commit, part of
> xlog_state_release_iclog() was open-coded into
> xfs_log_release_iclog() and as a result the locked error state check
> was lost.
> 
> The lockless check still exists, but this doesn't account for the
> possibility of a race with a shutdown being performed by another
> task causing the iclog state to change while the original task waits
> on ->l_icloglock. This has reproduced very rarely via generic/475
> and manifests as an assert failure in __xlog_state_release_iclog()
> due to an unexpected iclog state.
> 
> Restore the locked error state check in xlog_state_release_iclog()
> to ensure that an iclog state update via shutdown doesn't race with
> the iclog release state processing code.

Btw, from code inspection I think we also need the same check after
taking the lock in xlog_state_release_iclog.