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>
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@ -784,8 +784,12 @@ static bool nfsd41_cb_get_slot(struct nfs4_client *clp, struct rpc_task *task)
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{
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if (test_and_set_bit(0, &clp->cl_cb_slot_busy) != 0) {
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rpc_sleep_on(&clp->cl_cb_waitq, task, NULL);
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dprintk("%s slot is busy\n", __func__);
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return false;
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/* Race breaker */
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if (test_and_set_bit(0, &clp->cl_cb_slot_busy) != 0) {
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dprintk("%s slot is busy\n", __func__);
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return false;
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}
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rpc_wake_up_queued_task(&clp->cl_cb_waitq, task);
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}
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return true;
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}
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