diff options
| author | Nathaniel W. Turner <nate@houseofnate.net> | 2009-11-16 19:51:48 +0000 |
|---|---|---|
| committer | Alex Elder <aelder@sgi.com> | 2009-11-17 10:26:49 -0600 |
| commit | 6c06f072c2d797ddbb2270363de97c53ebbe0385 (patch) | |
| tree | 03654fd6af68f5ba0004f9e7c2b6945504de53f3 /fs/xfs | |
| parent | 8ec6dba2581754e375be66f7bedd708d856d8b30 (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/xfs')
| -rw-r--r-- | fs/xfs/xfs_trans_ail.c | 23 |
1 files changed, 20 insertions, 3 deletions
diff --git a/fs/xfs/xfs_trans_ail.c b/fs/xfs/xfs_trans_ail.c index f31271c30de9..2ffc570679be 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); } |