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xfs: make AIL target updates and compares 32bit safe.
The recent conversion of the xfsaild functionality to a work queue introduced a hard-to-hit log space grant hang. One of the problems noticed was that updates of the push target are not 32 bit safe as the target is a 64 bit value. We cannot copy a 64 bit LSN without the possibility of corrupting the result when racing with another updating thread. We have function to do this update safely without needing to care about 32/64 bit issues - xfs_trans_ail_copy_lsn() - so use that when updating the AIL push target. Also move the reading of the target in the push work inside the AIL lock, and use XFS_LSN_CMP() for the unlocked comparison during work termination to close read holes as well. Signed-off-by: Dave Chinner <david@fromorbit.com> Reviewed-by: Christoph Hellwig <hch@lst.de> Reviewed-by: Alex Elder <aelder@sgi.com>
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1 changed files with 4 additions and 3 deletions
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@ -354,7 +354,7 @@ xfs_ail_worker(
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struct xfs_ail_cursor *cur = &ailp->xa_cursors;
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xfs_log_item_t *lip;
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xfs_lsn_t lsn;
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xfs_lsn_t target = ailp->xa_target;
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xfs_lsn_t target;
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long tout = 10;
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int flush_log = 0;
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int stuck = 0;
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@ -362,6 +362,7 @@ xfs_ail_worker(
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int push_xfsbufd = 0;
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spin_lock(&ailp->xa_lock);
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target = ailp->xa_target;
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xfs_trans_ail_cursor_init(ailp, cur);
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lip = xfs_trans_ail_cursor_first(ailp, cur, ailp->xa_last_pushed_lsn);
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if (!lip || XFS_FORCED_SHUTDOWN(mp)) {
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@ -491,7 +492,7 @@ xfs_ail_worker(
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* work to do. Wait a bit longer before starting that work.
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*/
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smp_rmb();
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if (ailp->xa_target == target) {
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if (XFS_LSN_CMP(ailp->xa_target, target) == 0) {
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clear_bit(XFS_AIL_PUSHING_BIT, &ailp->xa_flags);
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return;
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}
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@ -553,7 +554,7 @@ xfs_ail_push(
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* the XFS_AIL_PUSHING_BIT.
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*/
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smp_wmb();
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ailp->xa_target = threshold_lsn;
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xfs_trans_ail_copy_lsn(ailp, &ailp->xa_target, &threshold_lsn);
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if (!test_and_set_bit(XFS_AIL_PUSHING_BIT, &ailp->xa_flags))
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queue_delayed_work(xfs_syncd_wq, &ailp->xa_work, 0);
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}
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