[Ocfs2-devel] [PATCH] ocfs2: fix a tiny race that leads file system read-only

[xuejiufei]

when o2hb detect a node down, it first set the dead node to recovery
map and create ocfs2rec which will replay journal for dead node.
o2hb thread then call dlm_do_local_recovery_cleanup() to delete the
lock for dead node. After the lock of dead node is gone, locks for other
nodes can be granted and may modify the meta data without replaying
journal of the dead node. The detail is described as follows.

     N1                         N2                   N3(master)
modify the extent tree of
inode, and commit
dirty metadata to journal,
then goes down.
                                                 o2hb thread detects
                                                 N1 goes down, set
                                                 recovery map and
                                                 delete the lock of N1.

                                                 dlm_thread flush ast
                                                 for the lock of N2.
                        do not detect the death
                        of N1, so recovery map is
                        empty.

                        read inode from disk
                        without replaying
                        the journal of N1 and
                        modify the extent tree
                        of the inode that N1
                        had modified.
                                                 ocfs2rec recover the
                                                 journal of N1.
                                                 The modification of N2
                                                 is lost.

The modification of N1 and N2 are not serial, and it will lead to
read-only file system. We can set recovery_waiting flag to the lock
resource after delete the lock for dead node to prevent other node
from getting the lock before dlm recovery. After dlm recovery, the
recovery map on N2 is not empty, ocfs2_inode_lock_full_nested() will
wait for ocfs2 recovery.

Signed-off-by: Jiufei Xue <xuejiufei at huawei.com>
---
 fs/ocfs2/dlm/dlmcommon.h   | 5 ++++-
 fs/ocfs2/dlm/dlmmaster.c   | 3 ++-
 fs/ocfs2/dlm/dlmrecovery.c | 8 ++++++++
 fs/ocfs2/dlm/dlmthread.c   | 6 ++++--
 4 files changed, 18 insertions(+), 4 deletions(-)

diff --git a/fs/ocfs2/dlm/dlmcommon.h b/fs/ocfs2/dlm/dlmcommon.h
index 68c607e..1276d91 100644
--- a/fs/ocfs2/dlm/dlmcommon.h
+++ b/fs/ocfs2/dlm/dlmcommon.h
@@ -282,6 +282,7 @@ static inline void __dlm_set_joining_node(struct dlm_ctxt *dlm,
 #define DLM_LOCK_RES_DROPPING_REF         0x00000040
 #define DLM_LOCK_RES_BLOCK_DIRTY          0x00001000
 #define DLM_LOCK_RES_SETREF_INPROG        0x00002000
+#define DLM_LOCK_RES_RECOVERY_WAITING     0x00004000

 /* max milliseconds to wait to sync up a network failure with a node death */
 #define DLM_NODE_DEATH_WAIT_MAX (5 * 1000)
@@ -789,7 +790,8 @@ __dlm_lockres_state_to_status(struct dlm_lock_resource *res)

 	assert_spin_locked(&res->spinlock);

-	if (res->state & DLM_LOCK_RES_RECOVERING)
+	if (res->state & (DLM_LOCK_RES_RECOVERING|
+			DLM_LOCK_RES_RECOVERY_WAITING))
 		status = DLM_RECOVERING;
 	else if (res->state & DLM_LOCK_RES_MIGRATING)
 		status = DLM_MIGRATING;
@@ -1009,6 +1011,7 @@ static inline void __dlm_wait_on_lockres(struct dlm_lock_resource *res)
 {
 	__dlm_wait_on_lockres_flags(res, (DLM_LOCK_RES_IN_PROGRESS|
 				    	  DLM_LOCK_RES_RECOVERING|
+					  DLM_LOCK_RES_RECOVERY_WAITING|
 					  DLM_LOCK_RES_MIGRATING));
 }

diff --git a/fs/ocfs2/dlm/dlmmaster.c b/fs/ocfs2/dlm/dlmmaster.c
index 9477d6e..12d385b 100644
--- a/fs/ocfs2/dlm/dlmmaster.c
+++ b/fs/ocfs2/dlm/dlmmaster.c
@@ -2432,7 +2432,8 @@ static int dlm_is_lockres_migrateable(struct dlm_ctxt *dlm,
 		return 0;

 	/* delay migration when the lockres is in RECOCERING state */
-	if (res->state & DLM_LOCK_RES_RECOVERING)
+	if (res->state & (DLM_LOCK_RES_RECOVERING|
+			DLM_LOCK_RES_RECOVERY_WAITING))
 		return 0;

 	if (res->owner != dlm->node_num)
diff --git a/fs/ocfs2/dlm/dlmrecovery.c b/fs/ocfs2/dlm/dlmrecovery.c
index b94a425..099714e 100644
--- a/fs/ocfs2/dlm/dlmrecovery.c
+++ b/fs/ocfs2/dlm/dlmrecovery.c
@@ -2163,6 +2163,13 @@ static void dlm_finish_local_lockres_recovery(struct dlm_ctxt *dlm,
 	for (i = 0; i < DLM_HASH_BUCKETS; i++) {
 		bucket = dlm_lockres_hash(dlm, i);
 		hlist_for_each_entry(res, bucket, hash_node) {
+			if (res->state & DLM_LOCK_RES_RECOVERY_WAITING) {
+				spin_lock(&res->spinlock);
+				res->state &= ~DLM_LOCK_RES_RECOVERY_WAITING;
+				spin_unlock(&res->spinlock);
+				wake_up(&res->wq);
+			}
+
 			if (!(res->state & DLM_LOCK_RES_RECOVERING))
 				continue;

@@ -2300,6 +2307,7 @@ static void dlm_free_dead_locks(struct dlm_ctxt *dlm,
 			     res->lockname.len, res->lockname.name, freed, dead_node);
 			__dlm_print_one_lock_resource(res);
 		}
+		res->state |= DLM_LOCK_RES_RECOVERY_WAITING;
 		dlm_lockres_clear_refmap_bit(dlm, res, dead_node);
 	} else if (test_bit(dead_node, res->refmap)) {
 		mlog(0, "%s:%.*s: dead node %u had a ref, but had "
diff --git a/fs/ocfs2/dlm/dlmthread.c b/fs/ocfs2/dlm/dlmthread.c
index c5f6c24..73c03be 100644
--- a/fs/ocfs2/dlm/dlmthread.c
+++ b/fs/ocfs2/dlm/dlmthread.c
@@ -106,7 +106,8 @@ int __dlm_lockres_unused(struct dlm_lock_resource *res)
 	if (!list_empty(&res->dirty) || res->state & DLM_LOCK_RES_DIRTY)
 		return 0;

-	if (res->state & DLM_LOCK_RES_RECOVERING)
+	if (res->state & (DLM_LOCK_RES_RECOVERING|
+			DLM_LOCK_RES_RECOVERY_WAITING))
 		return 0;

 	/* Another node has this resource with this node as the master */
@@ -700,7 +701,8 @@ static int dlm_thread(void *data)
 			 * dirty for a short while. */
 			BUG_ON(res->state & DLM_LOCK_RES_MIGRATING);
 			if (res->state & (DLM_LOCK_RES_IN_PROGRESS |
-					  DLM_LOCK_RES_RECOVERING)) {
+					  DLM_LOCK_RES_RECOVERING |
+					  DLM_LOCK_RES_RECOVERY_WAITING)) {
 				/* move it to the tail and keep going */
 				res->state &= ~DLM_LOCK_RES_DIRTY;
 				spin_unlock(&res->spinlock);
-- 
1.8.4.3