Re: [PATCH] xfs: fix the forward progress assertion in xfs_iwalk_run_callbacks

[Zorro Lang <zlang@redhat.com>]

On Tue, Dec 08, 2020 at 09:16:51AM -0800, Darrick J. Wong wrote:
> From: Darrick J. Wong <darrick.wong@oracle.com>
> 
> In commit 27c14b5daa82 we started tracking the last inode seen during an
> inode walk to avoid infinite loops if a corrupt inobt record happens to
> have a lower ir_startino than the record preceeding it.  Unfortunately,
> the assertion trips over the case where there are completely empty inobt
> records (which can happen quite easily on 64k page filesystems) because
> we advance the tracking cursor without actually putting the empty record
> into the processing buffer.  Fix the assert to allow for this case.
> 
> Reported-by: zlang@redhat.com
> Fixes: 27c14b5daa82 ("xfs: ensure inobt record walks always make forward progress")
> Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
> ---

Looks good to me, and I just gave it a test on the same P9 machine which triggered
this bug, test passed.

Reviewed-by: Zorro Lang <zlang@redhat.com>

>  fs/xfs/xfs_iwalk.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/xfs/xfs_iwalk.c b/fs/xfs/xfs_iwalk.c
> index 2a45138831e3..eae3aff9bc97 100644
> --- a/fs/xfs/xfs_iwalk.c
> +++ b/fs/xfs/xfs_iwalk.c
> @@ -363,7 +363,7 @@ xfs_iwalk_run_callbacks(
>  	/* Delete cursor but remember the last record we cached... */
>  	xfs_iwalk_del_inobt(tp, curpp, agi_bpp, 0);
>  	irec = &iwag->recs[iwag->nr_recs - 1];
> -	ASSERT(next_agino == irec->ir_startino + XFS_INODES_PER_CHUNK);
> +	ASSERT(next_agino >= irec->ir_startino + XFS_INODES_PER_CHUNK);
>  
>  	error = xfs_iwalk_ag_recs(iwag);
>  	if (error)
>