The patch titled
Subject: ocfs2: o2dlm: fix a race between purge and master query
has been added to the -mm tree. Its filename is
o2dlm-fix-a-race-between-purge-and-master-query.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/o2dlm-fix-a-race-between-purge-and-master-query.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/o2dlm-fix-a-race-between-purge-and-master-query.patch
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------------------------------------------------------
From: Srinivas Eeda <srinivas.eeda@xxxxxxxxxx>
Subject: ocfs2: o2dlm: fix a race between purge and master query
Node A sends master query request to node B which is the master. At this
time lockres happens to be on purgelist. dlm_master_request_handler gets
the dlm spinlock, finds the resource and releases the dlm spin lock.
Right at this dlm_thread on this node could purge the lockres.
dlm_master_request_handler can then acquire lockres spinlock and reply to
Node A that node B is the master even though lockres on node B is purged.
The above scenario will now make node A falsely think node B is the master
which is inconsistent. Further if another node C tries to master the same
resource, every node will respond they are not the master. Node C then
masters the resource and sends assert master to all nodes. This will now
make node A crash with the following message.
dlm_assert_master_handler:1831 ERROR: DIE! Mastery assert from 9, but current
owner is 10!
Signed-off-by: Srinivas Eeda <srinivas.eeda@xxxxxxxxxx>
Cc: Mark Fasheh <mfasheh@xxxxxxxx>
Cc: Joel Becker <jlbec@xxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
fs/ocfs2/dlm/dlmmaster.c | 12 ++++++++++++
1 file changed, 12 insertions(+)
diff -puN fs/ocfs2/dlm/dlmmaster.c~o2dlm-fix-a-race-between-purge-and-master-query fs/ocfs2/dlm/dlmmaster.c
--- a/fs/ocfs2/dlm/dlmmaster.c~o2dlm-fix-a-race-between-purge-and-master-query
+++ a/fs/ocfs2/dlm/dlmmaster.c
@@ -1460,6 +1460,18 @@ way_up_top:
/* take care of the easy cases up front */
spin_lock(&res->spinlock);
+
+ /*
+ * Right after dlm spinlock was released, dlm_thread could have
+ * purged the lockres. Check if lockres got unhashed. If so
+ * start over.
+ */
+ if (hlist_unhashed(&res->hash_node)) {
+ spin_unlock(&res->spinlock);
+ dlm_lockres_put(res);
+ goto way_up_top;
+ }
+
if (res->state & (DLM_LOCK_RES_RECOVERING|
DLM_LOCK_RES_MIGRATING)) {
spin_unlock(&res->spinlock);
_
Patches currently in -mm which might be from srinivas.eeda@xxxxxxxxxx are
o2dlm-fix-a-race-between-purge-and-master-query.patch
o2dlm-fix-null-pointer-dereference-in-o2dlm_blocking_ast_wrapper.patch
o2dlm-fix-null-pointer-dereference-in-o2dlm_blocking_ast_wrapper-checkpatch-fixes.patch
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