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[PULL 2/3] virtio-blk: simplify virtio_blk_dma_restart_cb()
From: |
Stefan Hajnoczi |
Subject: |
[PULL 2/3] virtio-blk: simplify virtio_blk_dma_restart_cb() |
Date: |
Mon, 23 Jan 2023 15:04:16 -0500 |
virtio_blk_dma_restart_cb() is tricky because the BH must deal with
virtio_blk_data_plane_start()/virtio_blk_data_plane_stop() being called.
There are two issues with the code:
1. virtio_blk_realize() should use qdev_add_vm_change_state_handler()
instead of qemu_add_vm_change_state_handler(). This ensures the
ordering with virtio_init()'s vm change state handler that calls
virtio_blk_data_plane_start()/virtio_blk_data_plane_stop() is
well-defined. Then blk's AioContext is guaranteed to be up-to-date in
virtio_blk_dma_restart_cb() and it's no longer necessary to have a
special case for virtio_blk_data_plane_start().
2. Only blk_drain() waits for virtio_blk_dma_restart_cb()'s
blk_inc_in_flight() to be decremented. The bdrv_drain() family of
functions do not wait for BlockBackend's in_flight counter to reach
zero. virtio_blk_data_plane_stop() relies on blk_set_aio_context()'s
implicit drain, but that's a bdrv_drain() and not a blk_drain().
Note that virtio_blk_reset() already correctly relies on blk_drain().
If virtio_blk_data_plane_stop() switches to blk_drain() then we can
properly wait for pending virtio_blk_dma_restart_bh() calls.
Once these issues are taken care of the code becomes simpler. This
change is in preparation for multiple IOThreads in virtio-blk where we
need to clean up the multi-threading behavior.
I ran the reproducer from commit 49b44549ace7 ("virtio-blk: On restart,
process queued requests in the proper context") to check that there is
no regression.
Cc: Sergio Lopez <slp@redhat.com>
Cc: Kevin Wolf <kwolf@redhat.com>
Cc: Emanuele Giuseppe Esposito <eesposit@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
Message-id: 20221102182337.252202-1-stefanha@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
---
include/hw/virtio/virtio-blk.h | 2 --
hw/block/dataplane/virtio-blk.c | 17 +++++-------
hw/block/virtio-blk.c | 46 ++++++++++++++-------------------
3 files changed, 26 insertions(+), 39 deletions(-)
diff --git a/include/hw/virtio/virtio-blk.h b/include/hw/virtio/virtio-blk.h
index 7f589b4146..dafec432ce 100644
--- a/include/hw/virtio/virtio-blk.h
+++ b/include/hw/virtio/virtio-blk.h
@@ -55,7 +55,6 @@ struct VirtIOBlock {
VirtIODevice parent_obj;
BlockBackend *blk;
void *rq;
- QEMUBH *bh;
VirtIOBlkConf conf;
unsigned short sector_mask;
bool original_wce;
@@ -93,6 +92,5 @@ typedef struct MultiReqBuffer {
} MultiReqBuffer;
void virtio_blk_handle_vq(VirtIOBlock *s, VirtQueue *vq);
-void virtio_blk_process_queued_requests(VirtIOBlock *s, bool is_bh);
#endif
diff --git a/hw/block/dataplane/virtio-blk.c b/hw/block/dataplane/virtio-blk.c
index 26f965cabc..b28d81737e 100644
--- a/hw/block/dataplane/virtio-blk.c
+++ b/hw/block/dataplane/virtio-blk.c
@@ -237,9 +237,6 @@ int virtio_blk_data_plane_start(VirtIODevice *vdev)
goto fail_aio_context;
}
- /* Process queued requests before the ones in vring */
- virtio_blk_process_queued_requests(vblk, false);
-
/* Kick right away to begin processing requests already in vring */
for (i = 0; i < nvqs; i++) {
VirtQueue *vq = virtio_get_queue(s->vdev, i);
@@ -272,11 +269,6 @@ int virtio_blk_data_plane_start(VirtIODevice *vdev)
fail_host_notifiers:
k->set_guest_notifiers(qbus->parent, nvqs, false);
fail_guest_notifiers:
- /*
- * If we failed to set up the guest notifiers queued requests will be
- * processed on the main context.
- */
- virtio_blk_process_queued_requests(vblk, false);
vblk->dataplane_disabled = true;
s->starting = false;
vblk->dataplane_started = true;
@@ -325,8 +317,13 @@ void virtio_blk_data_plane_stop(VirtIODevice *vdev)
aio_context_acquire(s->ctx);
aio_wait_bh_oneshot(s->ctx, virtio_blk_data_plane_stop_bh, s);
- /* Drain and try to switch bs back to the QEMU main loop. If other users
- * keep the BlockBackend in the iothread, that's ok */
+ /* Wait for virtio_blk_dma_restart_bh() and in flight I/O to complete */
+ blk_drain(s->conf->conf.blk);
+
+ /*
+ * Try to switch bs back to the QEMU main loop. If other users keep the
+ * BlockBackend in the iothread, that's ok
+ */
blk_set_aio_context(s->conf->conf.blk, qemu_get_aio_context(), NULL);
aio_context_release(s->ctx);
diff --git a/hw/block/virtio-blk.c b/hw/block/virtio-blk.c
index f717550fdc..1762517878 100644
--- a/hw/block/virtio-blk.c
+++ b/hw/block/virtio-blk.c
@@ -806,8 +806,10 @@ static void virtio_blk_handle_output(VirtIODevice *vdev,
VirtQueue *vq)
virtio_blk_handle_vq(s, vq);
}
-void virtio_blk_process_queued_requests(VirtIOBlock *s, bool is_bh)
+static void virtio_blk_dma_restart_bh(void *opaque)
{
+ VirtIOBlock *s = opaque;
+
VirtIOBlockReq *req = s->rq;
MultiReqBuffer mrb = {};
@@ -834,43 +836,27 @@ void virtio_blk_process_queued_requests(VirtIOBlock *s,
bool is_bh)
if (mrb.num_reqs) {
virtio_blk_submit_multireq(s, &mrb);
}
- if (is_bh) {
- blk_dec_in_flight(s->conf.conf.blk);
- }
+
+ /* Paired with inc in virtio_blk_dma_restart_cb() */
+ blk_dec_in_flight(s->conf.conf.blk);
+
aio_context_release(blk_get_aio_context(s->conf.conf.blk));
}
-static void virtio_blk_dma_restart_bh(void *opaque)
-{
- VirtIOBlock *s = opaque;
-
- qemu_bh_delete(s->bh);
- s->bh = NULL;
-
- virtio_blk_process_queued_requests(s, true);
-}
-
static void virtio_blk_dma_restart_cb(void *opaque, bool running,
RunState state)
{
VirtIOBlock *s = opaque;
- BusState *qbus = BUS(qdev_get_parent_bus(DEVICE(s)));
- VirtioBusState *bus = VIRTIO_BUS(qbus);
if (!running) {
return;
}
- /*
- * If ioeventfd is enabled, don't schedule the BH here as queued
- * requests will be processed while starting the data plane.
- */
- if (!s->bh && !virtio_bus_ioeventfd_enabled(bus)) {
- s->bh = aio_bh_new(blk_get_aio_context(s->conf.conf.blk),
- virtio_blk_dma_restart_bh, s);
- blk_inc_in_flight(s->conf.conf.blk);
- qemu_bh_schedule(s->bh);
- }
+ /* Paired with dec in virtio_blk_dma_restart_bh() */
+ blk_inc_in_flight(s->conf.conf.blk);
+
+ aio_bh_schedule_oneshot(blk_get_aio_context(s->conf.conf.blk),
+ virtio_blk_dma_restart_bh, s);
}
static void virtio_blk_reset(VirtIODevice *vdev)
@@ -1213,7 +1199,13 @@ static void virtio_blk_device_realize(DeviceState *dev,
Error **errp)
return;
}
- s->change = qemu_add_vm_change_state_handler(virtio_blk_dma_restart_cb, s);
+ /*
+ * This must be after virtio_init() so virtio_blk_dma_restart_cb() gets
+ * called after ->start_ioeventfd() has already set blk's AioContext.
+ */
+ s->change =
+ qdev_add_vm_change_state_handler(dev, virtio_blk_dma_restart_cb, s);
+
blk_ram_registrar_init(&s->blk_ram_registrar, s->blk);
blk_set_dev_ops(s->blk, &virtio_block_ops, s);
--
2.39.0