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xfs: fix filesystsem freeze race in xfs_trans_alloc

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As pointed out by Jan xfs_trans_alloc can race with a concurrent filesystem
freeze when it sleeps during the memory allocation.  Fix this by moving the
wait_for_freeze call after the memory allocation.  This means moving the
freeze into the low-level _xfs_trans_alloc helper, which thus grows a new
argument.  Also fix up some comments in that area while at it.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Alex Elder <aelder@sgi.com>
Reviewed-by: Dave Chinner <david@fromorbit.com>
This commit is contained in:
Christoph Hellwig
2011-07-08 14:34:42 +02:00
parent 33b8f7c247
commit 7a249cf83d
5 changed files with 27 additions and 29 deletions
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14
fs/xfs/xfs_mount.c
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@@ -1566,15 +1566,9 @@ xfs_fs_writable(xfs_mount_t *mp)
}
/*
* xfs_log_sbcount
*
* Called either periodically to keep the on disk superblock values
* roughly up to date or from unmount to make sure the values are
* correct on a clean unmount.
*
* Note this code can be called during the process of freezing, so
* we may need to use the transaction allocator which does not not
* block when the transaction subsystem is in its frozen state.
*/
int
xfs_log_sbcount(
@@ -1596,7 +1590,13 @@ xfs_log_sbcount(
if (!xfs_sb_version_haslazysbcount(&mp->m_sb))
return 0;
tp = _xfs_trans_alloc(mp, XFS_TRANS_SB_COUNT, KM_SLEEP);
/*
* We can be called during the process of freezing, so make sure
* we go ahead even if the frozen for new transactions. We will
* always use a sync transaction in the freeze path to make sure
* the transaction has completed by the time we return.
*/
tp = _xfs_trans_alloc(mp, XFS_TRANS_SB_COUNT, KM_SLEEP, false);
error = xfs_trans_reserve(tp, 0, mp->m_sb.sb_sectsize + 128, 0, 0,
XFS_DEFAULT_LOG_COUNT);
if (error) {