Commit c6c15e1e authored by Trond Myklebust's avatar Trond Myklebust Committed by J. Bruce Fields

nfsd: Fix slot wake up race in the nfsv4.1 callback code

The currect code for nfsd41_cb_get_slot() and nfsd4_cb_done() has no
locking in order to guarantee atomicity, and so allows for races of
the form.

Task 1                                  Task 2
======                                  ======
if (test_and_set_bit(0) != 0) {
                                        clear_bit(0)
                                        rpc_wake_up_next(queue)
        rpc_sleep_on(queue)
        return false;
}

This patch breaks the race condition by adding a retest of the bit
after the call to rpc_sleep_on().
Signed-off-by: default avatarTrond Myklebust <trond.myklebust@primarydata.com>
Cc: stable@vger.kernel.org
Signed-off-by: default avatarJ. Bruce Fields <bfields@redhat.com>
parent 093a1468
......@@ -774,8 +774,12 @@ static bool nfsd41_cb_get_slot(struct nfs4_client *clp, struct rpc_task *task)
{
if (test_and_set_bit(0, &clp->cl_cb_slot_busy) != 0) {
rpc_sleep_on(&clp->cl_cb_waitq, task, NULL);
dprintk("%s slot is busy\n", __func__);
return false;
/* Race breaker */
if (test_and_set_bit(0, &clp->cl_cb_slot_busy) != 0) {
dprintk("%s slot is busy\n", __func__);
return false;
}
rpc_wake_up_queued_task(&clp->cl_cb_waitq, task);
}
return true;
}
......
Markdown is supported
0%
or
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment