SUNRPC: allow svc_recv to break out of 500ms sleep when alloc_page fails

svc_recv() calls alloc_page(), and if it fails it does a 500ms
uninterruptible sleep and then reattempts. There doesn't seem to be any
real reason for this to be uninterruptible, so change it to an
interruptible sleep. Also check for kthread_stop() and signalled() after
setting the task state to avoid races that might lead to sleeping after
kthread_stop() wakes up the task.

I've done some very basic smoke testing with this, but obviously it's
hard to test the actual changes since this all depends on an
alloc_page() call failing.
Signed-off-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>

net/sunrpc/svc_xprt.c

@@ -587,10 +587,12 @@ int svc_recv(struct svc_rqst *rqstp, long timeout)
 		while (rqstp->rq_pages[i] == NULL) {
 			struct page *p = alloc_page(GFP_KERNEL);
 			if (!p) {
-				int j = msecs_to_jiffies(500);
-				if (kthread_should_stop())
+				set_current_state(TASK_INTERRUPTIBLE);
+				if (signalled() || kthread_should_stop()) {
+					set_current_state(TASK_RUNNING);
 					return -EINTR;
-				schedule_timeout_uninterruptible(j);
+				}
+				schedule_timeout(msecs_to_jiffies(500));
 			}
 			rqstp->rq_pages[i] = p;
 		}