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authorNathaniel W. Turner <nate@houseofnate.net>2009-11-16 19:51:48 +0000
committerAlex Elder <aelder@sgi.com>2009-11-17 10:26:49 -0600
commit6c06f072c2d797ddbb2270363de97c53ebbe0385 (patch)
tree03654fd6af68f5ba0004f9e7c2b6945504de53f3 /fs
parent8ec6dba2581754e375be66f7bedd708d856d8b30 (diff)
xfs: copy li_lsn before dropping AIL lock
Access to log items on the AIL is generally protected by m_ail_lock; this is particularly needed when we're getting or setting the 64-bit li_lsn on a 32-bit platform. This patch fixes a couple places where we were accessing the log item after dropping the AIL lock on 32-bit machines. This can result in a partially-zeroed log->l_tail_lsn if xfs_trans_ail_delete is racing with xfs_trans_ail_update, and in at least some cases, this can leave the l_tail_lsn with a zero cycle number, which means xlog_space_left will think the log is full (unless CONFIG_XFS_DEBUG is set, in which case we'll trip an ASSERT), leading to processes stuck forever in xlog_grant_log_space. Thanks to Adrian VanderSpek for first spotting the race potential and to Dave Chinner for debug assistance. Signed-off-by: Nathaniel W. Turner <nate@houseofnate.net> Reviewed-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Alex Elder <aelder@sgi.com>
Diffstat (limited to 'fs')
-rw-r--r--fs/xfs/xfs_trans_ail.c23
1 files changed, 20 insertions, 3 deletions
diff --git a/fs/xfs/xfs_trans_ail.c b/fs/xfs/xfs_trans_ail.c
index f31271c30de..2ffc570679b 100644
--- a/fs/xfs/xfs_trans_ail.c
+++ b/fs/xfs/xfs_trans_ail.c
@@ -467,6 +467,7 @@ xfs_trans_ail_update(
{
xfs_log_item_t *dlip = NULL;
xfs_log_item_t *mlip; /* ptr to minimum lip */
+ xfs_lsn_t tail_lsn;
mlip = xfs_ail_min(ailp);
@@ -483,8 +484,16 @@ xfs_trans_ail_update(
if (mlip == dlip) {
mlip = xfs_ail_min(ailp);
+ /*
+ * It is not safe to access mlip after the AIL lock is
+ * dropped, so we must get a copy of li_lsn before we do
+ * so. This is especially important on 32-bit platforms
+ * where accessing and updating 64-bit values like li_lsn
+ * is not atomic.
+ */
+ tail_lsn = mlip->li_lsn;
spin_unlock(&ailp->xa_lock);
- xfs_log_move_tail(ailp->xa_mount, mlip->li_lsn);
+ xfs_log_move_tail(ailp->xa_mount, tail_lsn);
} else {
spin_unlock(&ailp->xa_lock);
}
@@ -514,6 +523,7 @@ xfs_trans_ail_delete(
{
xfs_log_item_t *dlip;
xfs_log_item_t *mlip;
+ xfs_lsn_t tail_lsn;
if (lip->li_flags & XFS_LI_IN_AIL) {
mlip = xfs_ail_min(ailp);
@@ -527,9 +537,16 @@ xfs_trans_ail_delete(
if (mlip == dlip) {
mlip = xfs_ail_min(ailp);
+ /*
+ * It is not safe to access mlip after the AIL lock
+ * is dropped, so we must get a copy of li_lsn
+ * before we do so. This is especially important
+ * on 32-bit platforms where accessing and updating
+ * 64-bit values like li_lsn is not atomic.
+ */
+ tail_lsn = mlip ? mlip->li_lsn : 0;
spin_unlock(&ailp->xa_lock);
- xfs_log_move_tail(ailp->xa_mount,
- (mlip ? mlip->li_lsn : 0));
+ xfs_log_move_tail(ailp->xa_mount, tail_lsn);
} else {
spin_unlock(&ailp->xa_lock);
}