nfsd: Fix slot wake up race in the nfsv4.1 callback code
authorTrond Myklebust <trond.myklebust@primarydata.com>
Wed, 19 Nov 2014 17:47:50 +0000 (12:47 -0500)
committerJ. Bruce Fields <bfields@redhat.com>
Wed, 19 Nov 2014 20:45:44 +0000 (15:45 -0500)
commitc6c15e1ed303ffc47e696ea1c9a9df1761c1f603
tree14422719ae15d5d0cf05393169e485c4ac645fca
parent093a1468b6edb0e568be7311b8d2228d205702db
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: Trond Myklebust <trond.myklebust@primarydata.com>
Cc: stable@vger.kernel.org
Signed-off-by: J. Bruce Fields <bfields@redhat.com>
fs/nfsd/nfs4callback.c