This is a note to let you know that I've just added the patch titled
nfsd: Fix slot wake up race in the nfsv4.1 callback code
to the 3.17-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
nfsd-fix-slot-wake-up-race-in-the-nfsv4.1-callback-code.patch
and it can be found in the queue-3.17 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From c6c15e1ed303ffc47e696ea1c9a9df1761c1f603 Mon Sep 17 00:00:00 2001
From: Trond Myklebust <trond.myklebust@xxxxxxxxxxxxxxx>
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@xxxxxxxxxxxxxxx>
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@xxxxxxxxxxxxxxx>
Signed-off-by: J. Bruce Fields <bfields@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
fs/nfsd/nfs4callback.c | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)
--- a/fs/nfsd/nfs4callback.c
+++ b/fs/nfsd/nfs4callback.c
@@ -801,8 +801,12 @@ 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;
}
Patches currently in stable-queue which might be from trond.myklebust@xxxxxxxxxxxxxxx are
queue-3.17/nfsd-fix-slot-wake-up-race-in-the-nfsv4.1-callback-code.patch
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