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ocfs2: dlm: fix race between purge and get lock resource 

There is a race window in dlm_get_lock_resource(), which may return a
lock resource which has been purged.  This will cause the process to
hang forever in dlmlock() as the ast msg can't be handled due to its
lock resource not existing.

    dlm_get_lock_resource {
        ...
        spin_lock(&dlm->spinlock);
        tmpres = __dlm_lookup_lockres_full(dlm, lockid, namelen, hash);
        if (tmpres) {
             spin_unlock(&dlm->spinlock);
             >>>>>>>> race window, dlm_run_purge_list() may run and purge
                              the lock resource
             spin_lock(&tmpres->spinlock);
             ...
             spin_unlock(&tmpres->spinlock);
        }
    }

Signed-off-by: Junxiao Bi <junxiao.bi@oracle.com>
Cc: Joseph Qi <joseph.qi@huawei.com>
Cc: Mark Fasheh <mfasheh@suse.com>
Cc: Joel Becker <jlbec@evilplan.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Junxiao Bi 2015-05-05 16:24:02 -07:00 committed by Linus Torvalds
parent d8fd150fe3
commit b1432a2a35
1 changed files with 13 additions and 0 deletions
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13
fs/ocfs2/dlm/dlmmaster.c
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@ -757,6 +757,19 @@ struct dlm_lock_resource * dlm_get_lock_resource(struct dlm_ctxt *dlm,
if (tmpres) {
spin_unlock(&dlm->spinlock);
spin_lock(&tmpres->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(&tmpres->hash_node)) {
spin_unlock(&tmpres->spinlock);
dlm_lockres_put(tmpres);
tmpres = NULL;
goto lookup;
}
/* Wait on the thread that is mastering the resource */
if (tmpres->owner == DLM_LOCK_RES_OWNER_UNKNOWN) {
__dlm_wait_on_lockres(tmpres);