From: Trond Myklebust <trond.myklebust@primarydata.com>
Date: Wed, 19 Nov 2014 17:47:50 +0000 (-0500)
Subject: nfsd: Fix slot wake up race in the nfsv4.1 callback code
X-Git-Tag: v3.2.65~23
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=d74ea723036699f012b695ebf32e4f3b2c7d1fcc;p=pandora-kernel.git

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

commit c6c15e1ed303ffc47e696ea1c9a9df1761c1f603 upstream.

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>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---

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