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| author | Trond Myklebust <trond.myklebust@primarydata.com> | 2014-11-19 12:47:50 -0500 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2014-12-06 15:57:31 -0800 |
| commit | 1fe01fbe4220c6d91441aa6416275a6ef984a132 (patch) | |
| tree | 0660fd5d1a01547961c8d52045eb8899a7285a92 | |
| parent | d97056a5ec2b1a110499f6906fbe58865d21ee8a (diff) | |
| download | lwn-1fe01fbe4220c6d91441aa6416275a6ef984a132.tar.gz lwn-1fe01fbe4220c6d91441aa6416275a6ef984a132.zip | |
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.c | 8 |
1 files changed, 6 insertions, 2 deletions
diff --git a/fs/nfsd/nfs4callback.c b/fs/nfsd/nfs4callback.c index e0be57b0f79b..c6d7c879867e 100644 --- a/fs/nfsd/nfs4callback.c +++ b/fs/nfsd/nfs4callback.c @@ -801,8 +801,12 @@ 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; } |