From cb79662bc2f83f7b3b60970ad88df43085f96514 Mon Sep 17 00:00:00 2001 From: Srinivas Eeda Date: Wed, 10 Dec 2014 15:41:48 -0800 Subject: [PATCH] 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 Cc: Mark Fasheh Cc: Joel Becker Reviewed-by: Wengang Wang Tested-by: Joseph Qi Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- fs/ocfs2/dlm/dlmmaster.c | 12 ++++++++++++ 1 file changed, 12 insertions(+) diff --git a/fs/ocfs2/dlm/dlmmaster.c b/fs/ocfs2/dlm/dlmmaster.c index 215e41a..3689b35 100644 --- a/fs/ocfs2/dlm/dlmmaster.c +++ b/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); -- 2.7.4