nfsd: Fix slot wake up race in the nfsv4.1 callback code
commit c6c15e1ed3
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>
This commit is contained in:
parent
9942a780b6
commit
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@ -784,9 +784,13 @@ 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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/* 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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