Re: [PATCH 1/8] xfs: check for buffer errors before waiting

Dave Chinner
2012-03-29T21:10:29Z

On Thu, Mar 29, 2012 at 02:04:09PM -0500, Mark Tinguely wrote:
> On 03/29/12 07:23, Dave Chinner wrote:
> >From: Dave Chinner<dchinner@redhat.com>
> >
> >If we call xfs_buf_iowait() on a buffer that failed dispatch due to
> >an IO error, it will wait forever for an Io that does not exist.
> >This is hndled in xfs_buf_read, but there is other code that calls
> >xfs_buf_iowait directly that doesn't.
> >
> >Rather than make the call sites have to handle checking for dispatch
> >errors and then checking for completion errors, make
> >xfs_buf_iowait() check for dispatch errors on the buffer before
> >waiting. This means we handle both dispatch and completion errors
> >with one set of error handling at the caller sites.
> >
> >Signed-off-by: Dave Chinner<dchinner@redhat.com>
> >---
>
> >diff --git a/fs/xfs/xfs_log_recover.c b/fs/xfs/xfs_log_recover.c
> >index 396e3bf..64ed6ff 100644
> >--- a/fs/xfs/xfs_log_recover.c
> >+++ b/fs/xfs/xfs_log_recover.c
> >@@ -179,6 +179,7 @@ xlog_bread_noalign(
> > XFS_BUF_SET_ADDR(bp, log->l_logBBstart + blk_no);
> > XFS_BUF_READ(bp);
> > XFS_BUF_SET_COUNT(bp, BBTOB(nbblks));
> >+ bp->b_error = 0;
> >
> > xfsbdstrat(log->l_mp, bp);
> > error = xfs_buf_iowait(bp);
> >@@ -266,6 +267,7 @@ xlog_bwrite(
> > xfs_buf_hold(bp);
> > xfs_buf_lock(bp);
> > XFS_BUF_SET_COUNT(bp, BBTOB(nbblks));
> >+ bp->b_error = 0;
> >
> > error = xfs_bwrite(bp);
> > if (error)
>
> Just curious, were these needed for a particular reason?

If the previous user of the buffer got an error, it is not
guaranteed to be cleared because the buffer is not re-initialised.
i.e. it's an uncached buffer that we control completely and reuse
from IO to IO with just a reset of the bno and length. If b_error is
non zero here, then the IO can fail because nothing else clears the
error in the dispatch path....

Cheers,

Dave.
--
Dave Chinner
david@fromorbit.com