Re: [PATCH] xfs: restore shutdown check in mapped write fault path

[Gao Xiang <hsiangkao@redhat.com>]

On Wed, Feb 10, 2021 at 12:01:12PM -0500, Brian Foster wrote:
> XFS triggers an iomap warning in the write fault path due to a
> !PageUptodate() page if a write fault happens to occur on a page
> that recently failed writeback. The iomap writeback error handling
> code can clear the Uptodate flag if no portion of the page is
> submitted for I/O. This is reproduced by fstest generic/019, which
> combines various forms of I/O with simulated disk failures that
> inevitably lead to filesystem shutdown (which then unconditionally
> fails page writeback).
> 
> This is a regression introduced by commit f150b4234397 ("xfs: split
> the iomap ops for buffered vs direct writes") due to the removal of
> a shutdown check and explicit error return in the ->iomap_begin()
> path used by the write fault path. The explicit error return
> historically translated to a SIGBUS, but now carries on with iomap
> processing where it complains about the unexpected state. Restore
> the shutdown check to xfs_buffered_write_iomap_begin() to restore
> historical behavior.
> 
> Fixes: f150b4234397 ("xfs: split the iomap ops for buffered vs direct writes")
> Signed-off-by: Brian Foster <bfoster@redhat.com>

Taking some time on the internal discussion thread, I also think
SIGBUS is also appropriate after fs shutdown rather than dirty
this page anyway.

Reviewed-by: Gao Xiang <hsiangkao@redhat.com>

Thanks,
Gao Xiang