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xfs: rework xfs_buf_bio_endio error handling

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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: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Dave Chinner <david@fromorbit.com>
This commit is contained in:
Dave Chinner 2014-10-02 09:04:31 +10:00 committed by Dave Chinner
parent e8aaba9a78
commit 61be9c529a
2 changed files with 17 additions and 2 deletions
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18
fs/xfs/xfs_buf.c
View file

@ -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

1
fs/xfs/xfs_buf.h
View file

@ -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 */