xfs: dummy transactions should not dirty VFS state

When we  need to cover the log, we issue dummy transactions to ensure
the current log tail is on disk. Unfortunately we currently use the
root inode in the dummy transaction, and the act of committing the
transaction dirties the inode at the VFS level.

As a result, the VFS writeback of the dirty inode will prevent the
filesystem from idling long enough for the log covering state
machine to complete. The state machine gets stuck in a loop issuing
new dummy transactions to cover the log and never makes progress.

To avoid this problem, the dummy transactions should not cause
externally visible state changes. To ensure this occurs, make sure
that dummy transactions log an unchanging field in the superblock as
it's state is never propagated outside the filesystem. This allows
the log covering state machine to complete successfully and the
filesystem now correctly enters a fully idle state about 90s after
the last modification was made.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>

diff --git a/fs/xfs/linux-2.6/xfs_super.c b/fs/xfs/linux-2.6/xfs_super.c
index c6b24e7c308a94ee7d4a9e2b4c7daabbea875c97..a4e07974955be3025ebbbe3839264b9bb1acba74 100644 (file)
--- a/fs/xfs/linux-2.6/xfs_super.c
+++ b/fs/xfs/linux-2.6/xfs_super.c
@@ -1407,7 +1407,7 @@ xfs_fs_freeze(
 
        xfs_save_resvblks(mp);
        xfs_quiesce_attr(mp);
-       return -xfs_fs_log_dummy(mp);
+       return -xfs_fs_log_dummy(mp, SYNC_WAIT);
 }
 
 STATIC int

diff --git a/fs/xfs/linux-2.6/xfs_sync.c b/fs/xfs/linux-2.6/xfs_sync.c
index dfcbd98d15997e62e7d8a433fa71e5b8a9912609..d59c4a65d492c9b6b0713accaec1ab1c2ba7ea5f 100644 (file)
--- a/fs/xfs/linux-2.6/xfs_sync.c
+++ b/fs/xfs/linux-2.6/xfs_sync.c
@@ -34,6 +34,7 @@
 #include "xfs_inode_item.h"
 #include "xfs_quota.h"
 #include "xfs_trace.h"
+#include "xfs_fsops.h"
 
 #include <linux/kthread.h>
 #include <linux/freezer.h>
@@ -340,38 +341,6 @@ xfs_sync_attr(
                                     XFS_ICI_NO_TAG, 0, NULL);
 }
 
-STATIC int
-xfs_commit_dummy_trans(
-       struct xfs_mount        *mp,
-       uint                    flags)
-{
-       struct xfs_inode        *ip = mp->m_rootip;
-       struct xfs_trans        *tp;
-       int                     error;
-
-       /*
-        * Put a dummy transaction in the log to tell recovery
-        * that all others are OK.
-        */
-       tp = xfs_trans_alloc(mp, XFS_TRANS_DUMMY1);
-       error = xfs_trans_reserve(tp, 0, XFS_ICHANGE_LOG_RES(mp), 0, 0, 0);
-       if (error) {
-               xfs_trans_cancel(tp, 0);
-               return error;
-       }
-
-       xfs_ilock(ip, XFS_ILOCK_EXCL);
-
-       xfs_trans_ijoin(tp, ip);
-       xfs_trans_log_inode(tp, ip, XFS_ILOG_CORE);
-       error = xfs_trans_commit(tp, 0);
-       xfs_iunlock(ip, XFS_ILOCK_EXCL);
-
-       /* the log force ensures this transaction is pushed to disk */
-       xfs_log_force(mp, (flags & SYNC_WAIT) ? XFS_LOG_SYNC : 0);
-       return error;
-}
-
 STATIC int
 xfs_sync_fsdata(
        struct xfs_mount        *mp)
@@ -432,7 +401,7 @@ xfs_quiesce_data(
 
        /* mark the log as covered if needed */
        if (xfs_log_need_covered(mp))
-               error2 = xfs_commit_dummy_trans(mp, SYNC_WAIT);
+               error2 = xfs_fs_log_dummy(mp, SYNC_WAIT);
 
        /* flush data-only devices */
        if (mp->m_rtdev_targp)
@@ -563,7 +532,7 @@ xfs_flush_inodes(
 /*
  * Every sync period we need to unpin all items, reclaim inodes and sync
  * disk quotas.  We might need to cover the log to indicate that the
- * filesystem is idle.
+ * filesystem is idle and not frozen.
  */
 STATIC void
 xfs_sync_worker(
@@ -577,8 +546,9 @@ xfs_sync_worker(
                xfs_reclaim_inodes(mp, 0);
                /* dgc: errors ignored here */
                error = xfs_qm_sync(mp, SYNC_TRYLOCK);
-               if (xfs_log_need_covered(mp))
-                       error = xfs_commit_dummy_trans(mp, 0);
+               if (mp->m_super->s_frozen == SB_UNFROZEN &&
+                   xfs_log_need_covered(mp))
+                       error = xfs_fs_log_dummy(mp, 0);
        }
        mp->m_sync_seq++;
        wake_up(&mp->m_wait_single_sync_task);

diff --git a/fs/xfs/xfs_fsops.c b/fs/xfs/xfs_fsops.c
index dbca5f5c37bad18fc220ce21f551d17b58f0c13a..43b1d56993350ba3af58c53757be99dfa936c017 100644 (file)
--- a/fs/xfs/xfs_fsops.c
+++ b/fs/xfs/xfs_fsops.c
@@ -604,31 +604,36 @@ out:
        return 0;
 }
 
+/*
+ * Dump a transaction into the log that contains no real change. This is needed
+ * to be able to make the log dirty or stamp the current tail LSN into the log
+ * during the covering operation.
+ *
+ * We cannot use an inode here for this - that will push dirty state back up
+ * into the VFS and then periodic inode flushing will prevent log covering from
+ * making progress. Hence we log a field in the superblock instead.
+ */
 int
 xfs_fs_log_dummy(
-       xfs_mount_t     *mp)
+       xfs_mount_t     *mp,
+       int             flags)
 {
        xfs_trans_t     *tp;
-       xfs_inode_t     *ip;
        int             error;
 
        tp = _xfs_trans_alloc(mp, XFS_TRANS_DUMMY1, KM_SLEEP);
-       error = xfs_trans_reserve(tp, 0, XFS_ICHANGE_LOG_RES(mp), 0, 0, 0);
+       error = xfs_trans_reserve(tp, 0, mp->m_sb.sb_sectsize + 128, 0, 0,
+                                       XFS_DEFAULT_LOG_COUNT);
        if (error) {
                xfs_trans_cancel(tp, 0);
                return error;
        }
 
-       ip = mp->m_rootip;
-       xfs_ilock(ip, XFS_ILOCK_EXCL);
-
-       xfs_trans_ijoin(tp, ip);
-       xfs_trans_log_inode(tp, ip, XFS_ILOG_CORE);
-       xfs_trans_set_sync(tp);
-       error = xfs_trans_commit(tp, 0);
-
-       xfs_iunlock(ip, XFS_ILOCK_EXCL);
-       return error;
+       /* log the UUID because it is an unchanging field */
+       xfs_mod_sb(tp, XFS_SB_UUID);
+       if (flags & SYNC_WAIT)
+               xfs_trans_set_sync(tp);
+       return xfs_trans_commit(tp, 0);
 }
 
 int

diff --git a/fs/xfs/xfs_fsops.h b/fs/xfs/xfs_fsops.h
index 88435e0a77c9b2f67035344e8f3afc58532d4d5c..a786c5212c1e478677e46f2725105a010ebd1262 100644 (file)
--- a/fs/xfs/xfs_fsops.h
+++ b/fs/xfs/xfs_fsops.h
@@ -25,6 +25,6 @@ extern int xfs_fs_counts(xfs_mount_t *mp, xfs_fsop_counts_t *cnt);
 extern int xfs_reserve_blocks(xfs_mount_t *mp, __uint64_t *inval,
                                xfs_fsop_resblks_t *outval);
 extern int xfs_fs_goingdown(xfs_mount_t *mp, __uint32_t inflags);
-extern int xfs_fs_log_dummy(xfs_mount_t *mp);
+extern int xfs_fs_log_dummy(xfs_mount_t *mp, int flags);
 
 #endif /* __XFS_FSOPS_H__ */