xfs: make AIL target updates and compares 32bit safe. (fd5670f2) · Commits · 戴 / test

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>

fs/xfs/xfs_trans_ail.c

+4 −3

Original line number	Diff line number	Diff line
		@@ -354,7 +354,7 @@ xfs_ail_worker(
		struct xfs_ail_cursor *cur = &ailp->xa_cursors;
		xfs_log_item_t *lip;
		xfs_lsn_t lsn;
		xfs_lsn_t target = ailp->xa_target;
		xfs_lsn_t target;
		long tout = 10;
		int flush_log = 0;
		int stuck = 0;
		@@ -362,6 +362,7 @@ xfs_ail_worker(
		int push_xfsbufd = 0;

		spin_lock(&ailp->xa_lock);
		target = ailp->xa_target;
		xfs_trans_ail_cursor_init(ailp, cur);
		lip = xfs_trans_ail_cursor_first(ailp, cur, ailp->xa_last_pushed_lsn);
		if (!lip \|\| XFS_FORCED_SHUTDOWN(mp)) {
		@@ -491,7 +492,7 @@ out_done:
		* work to do. Wait a bit longer before starting that work.
		*/
		smp_rmb();
		if (ailp->xa_target == target) {
		if (XFS_LSN_CMP(ailp->xa_target, target) == 0) {
		clear_bit(XFS_AIL_PUSHING_BIT, &ailp->xa_flags);
		return;
		}
		@@ -553,7 +554,7 @@ xfs_ail_push(
		* the XFS_AIL_PUSHING_BIT.
		*/
		smp_wmb();
		ailp->xa_target = threshold_lsn;
		xfs_trans_ail_copy_lsn(ailp, &ailp->xa_target, &threshold_lsn);
		if (!test_and_set_bit(XFS_AIL_PUSHING_BIT, &ailp->xa_flags))
		queue_delayed_work(xfs_syncd_wq, &ailp->xa_work, 0);
		}

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