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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>
This commit is contained in:
Dave Chinner 2011-05-06 02:54:07 +00:00 committed by Alex Elder
parent cb64026b6e
commit fd5670f22f
1 changed files with 4 additions and 3 deletions
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7
fs/xfs/xfs_trans_ail.c
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@ -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);
}