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Commit 61be9c52 authored by Dave Chinner's avatar Dave Chinner Committed by Dave Chinner
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xfs: rework xfs_buf_bio_endio error handling 



Currently the report of a bio error from completion
immediately marks the buffer with an error. The issue is that this
is racy w.r.t. synchronous IO - the submitter can see b_error being
set before the IO is complete, and hence we cannot differentiate
between submission failures and completion failures.

Add an internal b_io_error field protected by the b_lock to catch IO
completion errors, and only propagate that to the buffer during
final IO completion handling. Hence we can tell in xfs_buf_iorequest
if we've had a submission failure bey checking bp->b_error before
dropping our b_io_remaining reference - that reference will prevent
b_io_error values from being propagated to b_error in the event that
completion races with submission.

Signed-off-by: default avatarDave Chinner <dchinner@redhat.com>
Reviewed-by: default avatarChristoph Hellwig <hch@lst.de>
Signed-off-by: default avatarDave Chinner <david@fromorbit.com>
parent e8aaba9a

fs/xfs/xfs_buf.c

+16 −2
Original line number Diff line number Diff line
@@ -1008,6 +1008,13 @@ xfs_buf_ioend( 


	bp->b_flags &= ~(XBF_READ | XBF_WRITE | XBF_READ_AHEAD);



	/*

	 * Pull in IO completion errors now. We are guaranteed to be running

	 * single threaded, so we don't need the lock to read b_io_error.

	 */

	if (!bp->b_error && bp->b_io_error)

		xfs_buf_ioerror(bp, bp->b_io_error);



	/* Only validate buffers that were read without errors */

	if (read && !bp->b_error && bp->b_ops) {

		ASSERT(!bp->b_iodone);
@@ -1192,8 +1199,12 @@ xfs_buf_bio_end_io( 
	 * don't overwrite existing errors - otherwise we can lose errors on

	 * buffers that require multiple bios to complete.

	 */

	if (!bp->b_error)

		xfs_buf_ioerror(bp, error);

	if (error) {

		spin_lock(&bp->b_lock);

		if (!bp->b_io_error)

			bp->b_io_error = error;

		spin_unlock(&bp->b_lock);

	}



	if (!bp->b_error && xfs_buf_is_vmapped(bp) && (bp->b_flags & XBF_READ))

		invalidate_kernel_vmap_range(bp->b_addr, xfs_buf_vmap_len(bp));
@@ -1379,6 +1390,9 @@ xfs_buf_iorequest( 
	if (bp->b_flags & XBF_WRITE)

		xfs_buf_wait_unpin(bp);



	/* clear the internal error state to avoid spurious errors */

	bp->b_io_error = 0;



	/*

	 * Take references to the buffer. For XBF_ASYNC buffers, holding a

	 * reference for as long as submission takes is all that is necessary

fs/xfs/xfs_buf.h

+1 −0
Original line number Diff line number Diff line
@@ -158,6 +158,7 @@ typedef struct xfs_buf { 
	struct list_head	b_lru;		/* lru list */

	spinlock_t		b_lock;		/* internal state lock */

	unsigned int		b_state;	/* internal state flags */

	int			b_io_error;	/* internal IO error state */

	wait_queue_head_t	b_waiters;	/* unpin waiters */

	struct list_head	b_list;

	struct xfs_perag	*b_pag;		/* contains rbtree root */