| From | lizf@kernel ... | Subject | [PATCH 3.4 009/176] nfsd: Fix slot wake up race in the nfsv4.1 callback code | Date | Thu, 9 Apr 2015 16:44:17 +0800 |
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From: Trond Myklebust <trond.myklebust@primarydata.com>
3.4.107-rc1 review patch. If anyone has any objections, please let me know.
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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: Zefan Li <lizefan@huawei.com> --- fs/nfsd/nfs4callback.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-)
diff --git a/fs/nfsd/nfs4callback.c b/fs/nfsd/nfs4callback.c index c8e9f63..ebf3f59 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; } -- 1.9.1
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