| From c6c15e1ed303ffc47e696ea1c9a9df1761c1f603 Mon Sep 17 00:00:00 2001 |
| From: Trond Myklebust <trond.myklebust@primarydata.com> |
| Date: Wed, 19 Nov 2014 12:47:50 -0500 |
| Subject: nfsd: Fix slot wake up race in the nfsv4.1 callback code |
| |
| From: Trond Myklebust <trond.myklebust@primarydata.com> |
| |
| 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> |
| |
| --- |
| fs/nfsd/nfs4callback.c | 8 ++++++-- |
| 1 file changed, 6 insertions(+), 2 deletions(-) |
| |
| --- a/fs/nfsd/nfs4callback.c |
| +++ b/fs/nfsd/nfs4callback.c |
| @@ -784,8 +784,12 @@ static bool nfsd41_cb_get_slot(struct nf |
| { |
| 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; |
| } |
