diff options
| author | Trond Myklebust <trond.myklebust@primarydata.com> | 2014-11-19 12:47:50 -0500 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2014-12-06 15:05:49 -0800 |
| commit | bfa09bfcfb3a6f172f3c6c623e5b376f8e73fd15 (patch) | |
| tree | b1f3c12641a8defbc36f66fc55dc8238fb789115 /fs | |
| parent | 158a695a37743947958ca415fcea2dbd88ee7661 (diff) | |
| download | lwn-bfa09bfcfb3a6f172f3c6c623e5b376f8e73fd15.tar.gz lwn-bfa09bfcfb3a6f172f3c6c623e5b376f8e73fd15.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>
Diffstat (limited to 'fs')
| -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 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; } |