ocfs2/dlm: fix a race between purge and migratio
PATCH 1/1 ocfs2/dlm: fix a race between purge and migratio
We found a race between purge and migration when doing code review. Node A put lockres to purgelist before receiving the migrate message from node B which is the master. dlm_mig_lockres_handler finds the lockres and releases the dlm spinlock. Then dlm_thread on node A can purge the lockres. dlm_mig_lockres_handler then gets the lockres spinlock and sends assert master message to tell other nodes that node A is the master now even lockres is purged. If node C set the master to node A, and another node D master the lockres because no node respond he is the master. That will make node C crash when node D send assert master to node C. So check if lockres gets unhashed in dlm_mig_lockres_handler to fix this race.
--- fs/ocfs2/dlm/dlmrecovery.c | 22 ++++++++++++++++++++++ 1 file changed, 22 insertions(+)
fs/ocfs2/dlm/dlmrecovery.c +22 -0
@@ -1400,11 +1400,33 @@ int dlm_mig_lockres_handler(struct o2net_msg *msg, u32 len, void *data,/* lookup the lock to see if we have a secondary queue for this * already... just add the locks in and this will have its owner * and RECOVERY flag changed when it completes. */ +way_up_top: res =dlm_lookup_lockres (dlm, mres->lockname, mres->lockname_len);if (res) {/* this will get a ref on res */ /* mark it as recovering/migrating and hash it */ 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; + } + +/* Wait on the resource purge to complete before continuing */ +if (res->state &DLM_LOCK_RES_DROPPING_REF ) { +__dlm_wait_on_lockres_flags (res, +DLM_LOCK_RES_DROPPING_REF ); +spin_unlock (&res->spinlock); +dlm_lockres_put (res); + goto way_up_top; + } +if (mres->flags &DLM_MRES_RECOVERY ) { res->state |=DLM_LOCK_RES_RECOVERING ; }else {
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1.8.4.3