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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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1
fs/xfs/xfs_buf.h
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@ -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 */