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    Subject[PATCH 3.2 075/164] ocfs2: dlm: fix race between purge and get lock resource
    3.2.70-rc1 review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Junxiao Bi <junxiao.bi@oracle.com>

    commit b1432a2a35565f538586774a03bf277c27fc267d upstream.

    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>
    Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
    Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
    Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
    ---
    fs/ocfs2/dlm/dlmmaster.c | 13 +++++++++++++
    1 file changed, 13 insertions(+)

    --- a/fs/ocfs2/dlm/dlmmaster.c
    +++ b/fs/ocfs2/dlm/dlmmaster.c
    @@ -729,6 +729,19 @@ lookup:
    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);


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