Re: Deadlock in net/sunrpc/sched.c

[Trond Myklebust <Trond.Myklebust@netapp.com>]

On Thu, 2006-03-02 at 18:51 +0100, Frederik Deweerdt wrote:
> (Added Trond Myklebust to the cc list, as he's working on sunrpc)
> > +	if (RPC_IS_QUEUED(task)) {
> > +		struct rpc_wait_queue *queue = task->u.tk_wait.rpc_waitq;
> > +		spin_lock_bh(&queue->lock);
> > +		if (rpc_start_wakeup(task))  {
> We may end up list_del'ing a task that is not queued
> anymore: we may be interrupted just after the RPC_IS_QUEUED test.
> Don't you think this patch could be enough?
> 
> --- linux-2.6.16-rc5/net/sunrpc/sched.c 2006-03-01 11:26:15.000000000 +0100
> +++ linux-2.6.16-rc5-2/net/sunrpc/sched.c       2006-03-02 15:43:18.000000000 +0100
> @@ -521,8 +521,7 @@
>         spin_lock_bh(&queue->lock);
>         head = &queue->tasks[queue->maxpriority];
>         for (;;) {
> -               while (!list_empty(head)) {
> -                       task = list_entry(head->next, struct rpc_task, u.tk_wait.list);
> +               list_for_each_entry(task, head, u.tk_wait.list) {
>                         __rpc_wake_up_task(task);
>                 }
>                 if (head == &queue->tasks[0])

You need a list_for_each_entry_safe() here, since __rpc_wake_up_task()
will cause the task to be removed from the list. See the patch I sent
out 1/2 hour ago.

Cheers
  Trond