The patch titled
Fix SUNRPC wakeup/execute race condition
has been added to the -mm tree. Its filename is
fix-sunrpc-wakeup-execute-race-condition.patch
See http://www.zip.com.au/~akpm/linux/patches/stuff/added-to-mm.txt to find
out what to do about this
------------------------------------------------------
Subject: Fix SUNRPC wakeup/execute race condition
From: Christophe Saout <christophe@xxxxxxxx>
The sunrpc scheduler contains a race condition that can let an RPC task end
up being neither running nor on any wait queue. The race takes place
between rpc_make_runnable (called from rpc_wake_up_task) and __rpc_execute
under the following condition:
First __rpc_execute calls tk_action which puts the task on some wait queue.
The task is dequeued by another process before __rpc_execute continues its
execution. While executing rpc_make_runnable exactly after setting the
task `running' bit and before clearing the `queued' bit __rpc_execute picks
up execution, clears `running' and subsequently both functions fall
through, both under the false assumption somebody else took the job.
Swapping rpc_test_and_set_running with rpc_clear_queued in
rpc_make_runnable fixes that hole. The reordering hopefully doesn't
introduce some new race condition, in fact the only possible one is already
correctly detected and handled in __rpc_execute.
Bug noticed on a 4-way x86_64 system under XEN with an NFSv4 server
on the same physical machine, apparently one of the few ways to hit
this race condition at all.
Cc: Trond Myklebust <trond.myklebust@xxxxxxxxxx>
Cc: J. Bruce Fields <bfields@xxxxxxxxxxxxxx>
Cc: Olaf Kirch <okir@xxxxxxxxxxxx>
Signed-off-by: Christophe Saout <christophe@xxxxxxxx>
Cc: Neil Brown <neilb@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxx>
---
net/sunrpc/sched.c | 5 +----
1 files changed, 1 insertion(+), 4 deletions(-)
diff -puN net/sunrpc/sched.c~fix-sunrpc-wakeup-execute-race-condition net/sunrpc/sched.c
--- a/net/sunrpc/sched.c~fix-sunrpc-wakeup-execute-race-condition
+++ a/net/sunrpc/sched.c
@@ -295,12 +295,9 @@ EXPORT_SYMBOL(__rpc_wait_for_completion_
*/
static void rpc_make_runnable(struct rpc_task *task)
{
- int do_ret;
-
BUG_ON(task->tk_timeout_fn);
- do_ret = rpc_test_and_set_running(task);
rpc_clear_queued(task);
- if (do_ret)
+ if (rpc_test_and_set_running(task))
return;
if (RPC_IS_ASYNC(task)) {
int status;
_
Patches currently in -mm which might be from christophe@xxxxxxxx are
fix-sunrpc-wakeup-execute-race-condition.patch
-
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