Hello Jason Wang,
The patch 030881372460: "vhost_net: basic polling support" from Mar
4, 2016, leads to the following
Smatch static checker warning:
drivers/vhost/vhost.c:2565 vhost_new_msg()
warn: sleeping in atomic context
vers/vhost/net.c
509 static void vhost_net_busy_poll(struct vhost_net *net,
510 struct vhost_virtqueue *rvq,
511 struct vhost_virtqueue *tvq,
512 bool *busyloop_intr,
513 bool poll_rx)
514 {
515 unsigned long busyloop_timeout;
516 unsigned long endtime;
517 struct socket *sock;
518 struct vhost_virtqueue *vq = poll_rx ? tvq : rvq;
519
520 /* Try to hold the vq mutex of the paired virtqueue. We can't
521 * use mutex_lock() here since we could not guarantee a
522 * consistenet lock ordering.
523 */
524 if (!mutex_trylock(&vq->mutex))
525 return;
526
527 vhost_disable_notify(&net->dev, vq);
528 sock = vhost_vq_get_backend(rvq);
529
530 busyloop_timeout = poll_rx ? rvq->busyloop_timeout:
531 tvq->busyloop_timeout;
532
533 preempt_disable();
^^^^^^^^^^^^^^^^^
This bumps the preemp_count.
I guess this is to disable page faults?
534 endtime = busy_clock() + busyloop_timeout;
535
536 while (vhost_can_busy_poll(endtime)) {
537 if (vhost_has_work(&net->dev)) {
538 *busyloop_intr = true;
539 break;
540 }
541
542 if ((sock_has_rx_data(sock) &&
543 !vhost_vq_avail_empty(&net->dev, rvq)) ||
The call tree from here to the GFP_KERNEL is very long...
vhost_vq_avail_empty()
-> vhost_get_avail_idx()
-> __vhost_get_user()
-> __vhost_get_user_slow()
-> translate_desc()
-> vhost_iotlb_miss vhost_new_msg() <-- GFP_KERNEL
544 !vhost_vq_avail_empty(&net->dev, tvq))
545 break;
546
547 cpu_relax();
548 }
549
550 preempt_enable();
551
552 if (poll_rx || sock_has_rx_data(sock))
553 vhost_net_busy_poll_try_queue(net, vq);
regards,
dan carpenter
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