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Subject[05/50] SUNRPC: Fix a race between work-queue and rpc_killall_tasks
2.6.33-longterm review patch.  If anyone has any objections, please let us know.

------------------
From: Trond Myklebust <Trond.Myklebust@netapp.com>

commit b55c59892e1f3b6c7d4b9ccffb4263e1486fb990 upstream.

Since rpc_killall_tasks may modify the rpc_task's tk_action field
without any locking, we need to be careful when dereferencing it.

Reported-by: Ben Greear <greearb@candelatech.com>
Tested-by: Ben Greear <greearb@candelatech.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
net/sunrpc/sched.c | 27 +++++++++++----------------
1 file changed, 11 insertions(+), 16 deletions(-)
--- a/net/sunrpc/sched.c
+++ b/net/sunrpc/sched.c
@@ -628,30 +628,25 @@ static void __rpc_execute(struct rpc_tas
BUG_ON(RPC_IS_QUEUED(task));

for (;;) {
+ void (*do_action)(struct rpc_task *);

/*
- * Execute any pending callback.
+ * Execute any pending callback first.
*/
- if (task->tk_callback) {
- void (*save_callback)(struct rpc_task *);
-
- /*
- * We set tk_callback to NULL before calling it,
- * in case it sets the tk_callback field itself:
- */
- save_callback = task->tk_callback;
- task->tk_callback = NULL;
- save_callback(task);
- } else {
+ do_action = task->tk_callback;
+ task->tk_callback = NULL;
+ if (do_action == NULL) {
/*
* Perform the next FSM step.
- * tk_action may be NULL when the task has been killed
- * by someone else.
+ * tk_action may be NULL if the task has been killed.
+ * In particular, note that rpc_killall_tasks may
+ * do this at any time, so beware when dereferencing.
*/
- if (task->tk_action == NULL)
+ do_action = task->tk_action;
+ if (do_action == NULL)
break;
- task->tk_action(task);
}
+ do_action(task);

/*
* Lockless check for whether task is sleeping or not.



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