Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1761973AbZLJWf1 (ORCPT ); Thu, 10 Dec 2009 17:35:27 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1761822AbZLJWfY (ORCPT ); Thu, 10 Dec 2009 17:35:24 -0500 Received: from e31.co.us.ibm.com ([32.97.110.149]:58804 "EHLO e31.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1761248AbZLJWfX (ORCPT ); Thu, 10 Dec 2009 17:35:23 -0500 Subject: [PATCH] virtio: Fix scheduling while atomic in virtio_balloon stats From: Adam Litke To: Rusty Russell Cc: Anthony Liguori , linux-kernel@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Organization: IBM Date: Thu, 10 Dec 2009 16:35:15 -0600 Message-ID: <1260484515.4860.2.camel@aglitke> Mime-Version: 1.0 X-Mailer: Evolution 2.28.1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3601 Lines: 101 [PATCH] virtio: Fix scheduling while atomic in virtio_balloon stats This is a fix for my earlier patch: "virtio: Add memory statistics reporting to the balloon driver (V4)". I discovered that all_vm_events() can sleep and therefore stats collection cannot be done in interrupt context. One solution is to handle the interrupt by noting that stats need to be collected and waking the existing vballoon kthread which will complete the work via stats_handle_request(). Rusty, is this a saner way of doing business? There is one issue that I would like a broader opinion on. In stats_request, I update vb->need_stats_update and then wake up the kthread. The kthread uses vb->need_stats_update as a condition variable. Do I need a memory barrier between the update and wake_up to ensure that my kthread sees the correct value? My testing suggests that it is not needed but I would like some confirmation from the experts. Signed-off-by: Adam Litke To: Rusty Russell Cc: Anthony Liguori Cc: linux-kernel@vger.kernel.org diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c index b45d946..c4a6437 100644 --- a/drivers/virtio/virtio_balloon.c +++ b/drivers/virtio/virtio_balloon.c @@ -52,6 +52,7 @@ struct virtio_balloon u32 pfns[256]; /* Memory statistics */ + int need_stats_update; struct virtio_balloon_stat stats[VIRTIO_BALLOON_S_NR]; }; @@ -194,20 +195,30 @@ static void update_balloon_stats(struct virtio_balloon *vb) * the stats queue operates in reverse. The driver initializes the virtqueue * with a single buffer. From that point forward, all conversations consist of * a hypervisor request (a call to this function) which directs us to refill - * the virtqueue with a fresh stats buffer. + * the virtqueue with a fresh stats buffer. Since stats collection can sleep, + * we notify our kthread which does the actual work via stats_handle_request(). */ -static void stats_ack(struct virtqueue *vq) +static void stats_request(struct virtqueue *vq) { struct virtio_balloon *vb; unsigned int len; - struct scatterlist sg; vb = vq->vq_ops->get_buf(vq, &len); if (!vb) return; + vb->need_stats_update = 1; + wake_up(&vb->config_change); +} + +static void stats_handle_request(struct virtio_balloon *vb) +{ + struct virtqueue *vq; + struct scatterlist sg; + vb->need_stats_update = 0; update_balloon_stats(vb); + vq = vb->stats_vq; sg_init_one(&sg, vb->stats, sizeof(vb->stats)); if (vq->vq_ops->add_buf(vq, &sg, 1, 0, vb) < 0) BUG(); @@ -250,8 +261,11 @@ static int balloon(void *_vballoon) try_to_freeze(); wait_event_interruptible(vb->config_change, (diff = towards_target(vb)) != 0 + || vb->need_stats_update || kthread_should_stop() || freezing(current)); + if (vb->need_stats_update) + stats_handle_request(vb); if (diff > 0) fill_balloon(vb, diff); else if (diff < 0) @@ -265,7 +279,7 @@ static int virtballoon_probe(struct virtio_device *vdev) { struct virtio_balloon *vb; struct virtqueue *vqs[3]; - vq_callback_t *callbacks[] = { balloon_ack, balloon_ack, stats_ack }; + vq_callback_t *callbacks[] = { balloon_ack, balloon_ack, stats_request }; const char *names[] = { "inflate", "deflate", "stats" }; int err, nvqs; -- Thanks, Adam -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/