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SubjectRe: Deadlock in net/sunrpc/sched.c
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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
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