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authorTrond Myklebust <trond.myklebust@primarydata.com>2014-11-19 12:47:50 -0500
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2014-12-06 15:05:49 -0800
commitbfa09bfcfb3a6f172f3c6c623e5b376f8e73fd15 (patch)
treeb1f3c12641a8defbc36f66fc55dc8238fb789115
parent158a695a37743947958ca415fcea2dbd88ee7661 (diff)
downloadlinux-linaro-stable-bfa09bfcfb3a6f172f3c6c623e5b376f8e73fd15.tar.gz
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: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
-rw-r--r--fs/nfsd/nfs4callback.c8
1 files changed, 6 insertions, 2 deletions
diff --git a/fs/nfsd/nfs4callback.c b/fs/nfsd/nfs4callback.c
index cc8c5b32043c..f42bbe5fbc0a 100644
--- a/fs/nfsd/nfs4callback.c
+++ b/fs/nfsd/nfs4callback.c
@@ -784,8 +784,12 @@ 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;
}