[PULL 0/1] Block patches
[PULL 0/1] Block patches
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The following changes since commit 98b2e3c9ab3abfe476a2b02f8f51813edb90e72d:
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The following changes since commit 887cba855bb6ff4775256f7968409281350b568c:
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Merge remote-tracking branch 'remotes/stefanha/tags/block-pull-request' into staging (2019-10-08 16:08:35 +0100)
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configure: Fix cross-building for RISCV host (v5) (2023-07-11 17:56:09 +0100)
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are available in the Git repository at:
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are available in the Git repository at:
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https://github.com/stefanha/qemu.git tags/block-pull-request
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https://gitlab.com/stefanha/qemu.git tags/block-pull-request
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for you to fetch changes up to 69de48445a0d6169f1e2a6c5bfab994e1c810e33:
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for you to fetch changes up to 75dcb4d790bbe5327169fd72b185960ca58e2fa6:
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test-bdrv-drain: fix iothread_join() hang (2019-10-14 09:48:01 +0100)
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virtio-blk: fix host notifier issues during dataplane start/stop (2023-07-12 15:20:32 -0400)
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----------------------------------------------------------------
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----------------------------------------------------------------
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Pull request
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Pull request
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----------------------------------------------------------------
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----------------------------------------------------------------
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Stefan Hajnoczi (1):
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Stefan Hajnoczi (1):
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test-bdrv-drain: fix iothread_join() hang
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virtio-blk: fix host notifier issues during dataplane start/stop
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tests/iothread.c | 10 ++++++++--
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hw/block/dataplane/virtio-blk.c | 67 +++++++++++++++++++--------------
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1 file changed, 8 insertions(+), 2 deletions(-)
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1 file changed, 38 insertions(+), 29 deletions(-)
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--
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--
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2.21.0
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2.40.1
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diff view generated by jsdifflib
[PULL 1/1] test-bdrv-drain: fix iothread_join() hang
[PULL 1/1] virtio-blk: fix host notifier issues during dataplane start/stop
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tests/test-bdrv-drain can hang in tests/iothread.c:iothread_run():
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The main loop thread can consume 100% CPU when using --device
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virtio-blk-pci,iothread=<iothread>. ppoll() constantly returns but
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reading virtqueue host notifiers fails with EAGAIN. The file descriptors
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are stale and remain registered with the AioContext because of bugs in
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the virtio-blk dataplane start/stop code.
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while (!atomic_read(&iothread->stopping)) {
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The problem is that the dataplane start/stop code involves drain
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aio_poll(iothread->ctx, true);
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operations, which call virtio_blk_drained_begin() and
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}
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virtio_blk_drained_end() at points where the host notifier is not
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operational:
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- In virtio_blk_data_plane_start(), blk_set_aio_context() drains after
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vblk->dataplane_started has been set to true but the host notifier has
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not been attached yet.
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- In virtio_blk_data_plane_stop(), blk_drain() and blk_set_aio_context()
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drain after the host notifier has already been detached but with
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vblk->dataplane_started still set to true.
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The iothread_join() function works as follows:
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I would like to simplify ->ioeventfd_start/stop() to avoid interactions
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with drain entirely, but couldn't find a way to do that. Instead, this
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patch accepts the fragile nature of the code and reorders it so that
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vblk->dataplane_started is false during drain operations. This way the
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virtio_blk_drained_begin() and virtio_blk_drained_end() calls don't
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touch the host notifier. The result is that
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virtio_blk_data_plane_start() and virtio_blk_data_plane_stop() have
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complete control over the host notifier and stale file descriptors are
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no longer left in the AioContext.
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void iothread_join(IOThread *iothread)
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This patch fixes the 100% CPU consumption in the main loop thread and
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{
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correctly moves host notifier processing to the IOThread.
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iothread->stopping = true;
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aio_notify(iothread->ctx);
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qemu_thread_join(&iothread->thread);
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If iothread_run() checks iothread->stopping before the iothread_join()
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Fixes: 1665d9326fd2 ("virtio-blk: implement BlockDevOps->drained_begin()")
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thread sets stopping to true, then aio_notify() may be optimized away
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Reported-by: Lukáš Doktor <ldoktor@redhat.com>
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and iothread_run() hangs forever in aio_poll().
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Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
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Tested-by: Lukas Doktor <ldoktor@redhat.com>
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The correct way to change iothread->stopping is from a BH that executes
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Message-id: 20230704151527.193586-1-stefanha@redhat.com
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within iothread_run(). This ensures that iothread->stopping is checked
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after we set it to true.
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This was already fixed for ./iothread.c (note this is a different source
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file!) by commit 2362a28ea11c145e1a13ae79342d76dc118a72a6 ("iothread:
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fix iothread_stop() race condition"), but not for tests/iothread.c.
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Fixes: 0c330a734b51c177ab8488932ac3b0c4d63a718a
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("aio: introduce aio_co_schedule and aio_co_wake")
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Reported-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
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Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
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Message-Id: <20191003100103.331-1-stefanha@redhat.com>
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Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
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Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
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---
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---
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tests/iothread.c | 10 ++++++++--
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hw/block/dataplane/virtio-blk.c | 67 +++++++++++++++++++--------------
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1 file changed, 8 insertions(+), 2 deletions(-)
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1 file changed, 38 insertions(+), 29 deletions(-)
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diff --git a/tests/iothread.c b/tests/iothread.c
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diff --git a/hw/block/dataplane/virtio-blk.c b/hw/block/dataplane/virtio-blk.c
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index XXXXXXX..XXXXXXX 100644
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index XXXXXXX..XXXXXXX 100644
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--- a/tests/iothread.c
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--- a/hw/block/dataplane/virtio-blk.c
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+++ b/tests/iothread.c
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+++ b/hw/block/dataplane/virtio-blk.c
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@@ -XXX,XX +XXX,XX @@ static void *iothread_run(void *opaque)
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@@ -XXX,XX +XXX,XX @@ int virtio_blk_data_plane_start(VirtIODevice *vdev)
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return NULL;
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memory_region_transaction_commit();
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- /*
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- * These fields are visible to the IOThread so we rely on implicit barriers
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- * in aio_context_acquire() on the write side and aio_notify_accept() on
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- * the read side.
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- */
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- s->starting = false;
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- vblk->dataplane_started = true;
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trace_virtio_blk_data_plane_start(s);
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old_context = blk_get_aio_context(s->conf->conf.blk);
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@@ -XXX,XX +XXX,XX @@ int virtio_blk_data_plane_start(VirtIODevice *vdev)
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event_notifier_set(virtio_queue_get_host_notifier(vq));
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}
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+ /*
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+ * These fields must be visible to the IOThread when it processes the
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+ * virtqueue, otherwise it will think dataplane has not started yet.
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+ *
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+ * Make sure ->dataplane_started is false when blk_set_aio_context() is
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+ * called above so that draining does not cause the host notifier to be
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+ * detached/attached prematurely.
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+ */
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+ s->starting = false;
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+ vblk->dataplane_started = true;
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+ smp_wmb(); /* paired with aio_notify_accept() on the read side */
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+
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/* Get this show started by hooking up our callbacks */
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if (!blk_in_drain(s->conf->conf.blk)) {
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aio_context_acquire(s->ctx);
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@@ -XXX,XX +XXX,XX @@ int virtio_blk_data_plane_start(VirtIODevice *vdev)
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fail_guest_notifiers:
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vblk->dataplane_disabled = true;
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s->starting = false;
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- vblk->dataplane_started = true;
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return -ENOSYS;
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}
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}
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-void iothread_join(IOThread *iothread)
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@@ -XXX,XX +XXX,XX @@ void virtio_blk_data_plane_stop(VirtIODevice *vdev)
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+static void iothread_stop_bh(void *opaque)
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aio_wait_bh_oneshot(s->ctx, virtio_blk_data_plane_stop_bh, s);
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{
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}
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+ IOThread *iothread = opaque;
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+ /*
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+ * Batch all the host notifiers in a single transaction to avoid
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+ * quadratic time complexity in address_space_update_ioeventfds().
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+ */
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+ memory_region_transaction_begin();
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+
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+
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iothread->stopping = true;
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+ for (i = 0; i < nvqs; i++) {
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- aio_notify(iothread->ctx);
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+ virtio_bus_set_host_notifier(VIRTIO_BUS(qbus), i, false);
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+}
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+ }
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+
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+
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+void iothread_join(IOThread *iothread)
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+ /*
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+{
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+ * The transaction expects the ioeventfds to be open when it
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+ aio_bh_schedule_oneshot(iothread->ctx, iothread_stop_bh, iothread);
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+ * commits. Do it now, before the cleanup loop.
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qemu_thread_join(&iothread->thread);
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+ */
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qemu_cond_destroy(&iothread->init_done_cond);
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+ memory_region_transaction_commit();
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qemu_mutex_destroy(&iothread->init_done_lock);
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+
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+ for (i = 0; i < nvqs; i++) {
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+ virtio_bus_cleanup_host_notifier(VIRTIO_BUS(qbus), i);
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+ }
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+
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+ /*
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+ * Set ->dataplane_started to false before draining so that host notifiers
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+ * are not detached/attached anymore.
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+ */
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+ vblk->dataplane_started = false;
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+
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aio_context_acquire(s->ctx);
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/* Wait for virtio_blk_dma_restart_bh() and in flight I/O to complete */
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@@ -XXX,XX +XXX,XX @@ void virtio_blk_data_plane_stop(VirtIODevice *vdev)
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aio_context_release(s->ctx);
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- /*
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- * Batch all the host notifiers in a single transaction to avoid
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- * quadratic time complexity in address_space_update_ioeventfds().
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- */
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- memory_region_transaction_begin();
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-
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- for (i = 0; i < nvqs; i++) {
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- virtio_bus_set_host_notifier(VIRTIO_BUS(qbus), i, false);
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- }
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-
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- /*
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- * The transaction expects the ioeventfds to be open when it
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- * commits. Do it now, before the cleanup loop.
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- */
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- memory_region_transaction_commit();
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-
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- for (i = 0; i < nvqs; i++) {
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- virtio_bus_cleanup_host_notifier(VIRTIO_BUS(qbus), i);
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- }
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-
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qemu_bh_cancel(s->bh);
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notify_guest_bh(s); /* final chance to notify guest */
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/* Clean up guest notifier (irq) */
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k->set_guest_notifiers(qbus->parent, nvqs, false);
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- vblk->dataplane_started = false;
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s->stopping = false;
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}
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--
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--
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2.21.0
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2.40.1
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diff view generated by jsdifflib

Patchew 2.1-devel-b67e4c2

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