Commit cb79662b authored Dec 10, 2014 by Srinivas Eeda Committed by Linus Torvalds Dec 10, 2014

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@oracle.com>
Cc: Mark Fasheh <mfasheh@suse.com>
Cc: Joel Becker <jlbec@evilplan.org>
Reviewed-by: Wengang Wang <wen.gang.wang@oracle.com>
Tested-by: Joseph Qi <joseph.qi@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent f5425fce

fs/ocfs2/dlm/dlmmaster.c

+12 −0

Original line number	Diff line number	Diff line
		@@ -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);

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