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ocfs2: o2dlm: fix a race between purge and master query

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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>
This commit is contained in:
Srinivas Eeda 2014-12-10 15:41:48 -08:00 committed by Linus Torvalds
parent f5425fcea7
commit cb79662bc2
1 changed files with 12 additions and 0 deletions
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12
fs/ocfs2/dlm/dlmmaster.c
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@ -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);