[PATCH] [33/50] SUNRPC: Fix a race between work-queue and rpc_killall_tasks

Andi Kleen
2011-07-28T23:49:14Z

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

[ upstream commit b55c59892e1f3b6c7d4b9ccffb4263e1486fb990 ]

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>
Cc: stable@kernel.org
Signed-off-by: Andi Kleen <ak@linux.intel.com>

Index: linux-2.6.35.y/net/sunrpc/sched.c
===================================================================
--- linux-2.6.35.y.orig/net/sunrpc/sched.c
+++ linux-2.6.35.y/net/sunrpc/sched.c
@@ -623,30 +623,25 @@ 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.