Series comparison

-[Qemu-devel] [PULL for-3.0 0/1] Block patches
+[PULL 0/1] Block patches
-The following changes since commit 768cef2974fb1fa30dd188b043ea737e13fea477:
+The following changes since commit 887cba855bb6ff4775256f7968409281350b568c:
-  Merge remote-tracking branch 'remotes/ehabkost/tags/x86-next-pull-request' into staging (2018-07-24 10:37:52 +0100)
+  configure: Fix cross-building for RISCV host (v5) (2023-07-11 17:56:09 +0100)
 are available in the Git repository at:
-  git://github.com/stefanha/qemu.git tags/block-pull-request
+  https://gitlab.com/stefanha/qemu.git tags/block-pull-request
-for you to fetch changes up to 042b757cc77c9580b99ef2781cfb0a2d1bf495a6:
+for you to fetch changes up to 75dcb4d790bbe5327169fd72b185960ca58e2fa6:
-  block/file-posix: add bdrv_attach_aio_context callback for host dev and cdrom (2018-07-24 14:27:41 +0100)
+  virtio-blk: fix host notifier issues during dataplane start/stop (2023-07-12 15:20:32 -0400)
 ----------------------------------------------------------------
 Pull request
-Regression fix for host block devices with the file-posix driver when aio=native is in use.
 ----------------------------------------------------------------
-Nishanth Aravamudan (1):
+Stefan Hajnoczi (1):
-  block/file-posix: add bdrv_attach_aio_context callback for host dev
+  virtio-blk: fix host notifier issues during dataplane start/stop
     and cdrom
- block/file-posix.c | 3 +++
+ hw/block/dataplane/virtio-blk.c | 67 +++++++++++++++++++--------------
-file changed, 3 insertions(+)
+file changed, 38 insertions(+), 29 deletions(-)
 --
-.17.1
+.40.1

-[Qemu-devel] [PULL for-3.0 1/1] block/file-posix: add bdrv_attach_aio_context callback for host dev and cdrom
+[PULL 1/1] virtio-blk: fix host notifier issues during dataplane start/stop
-From: Nishanth Aravamudan <naravamudan@digitalocean.com>
+The main loop thread can consume 100% CPU when using --device
 virtio-blk-pci,iothread=<iothread>. ppoll() constantly returns but
 reading virtqueue host notifiers fails with EAGAIN. The file descriptors
 are stale and remain registered with the AioContext because of bugs in
 the virtio-blk dataplane start/stop code.
-In ed6e2161 ("linux-aio: properly bubble up errors from initialzation"),
+The problem is that the dataplane start/stop code involves drain
-I only added a bdrv_attach_aio_context callback for the bdrv_file
+operations, which call virtio_blk_drained_begin() and
-driver. There are several other drivers that use the shared
+virtio_blk_drained_end() at points where the host notifier is not
-aio_plug callback, though, and they will trip the assertion added to
+operational:
-aio_get_linux_aio because they did not call aio_setup_linux_aio first.
+- In virtio_blk_data_plane_start(), blk_set_aio_context() drains after
-Add the appropriate callback definition to the affected driver
+  vblk->dataplane_started has been set to true but the host notifier has
-definitions.
+  not been attached yet.
 - In virtio_blk_data_plane_stop(), blk_drain() and blk_set_aio_context()
   drain after the host notifier has already been detached but with
   vblk->dataplane_started still set to true.
-Fixes: ed6e2161 ("linux-aio: properly bubble up errors from initialization")
+I would like to simplify ->ioeventfd_start/stop() to avoid interactions
-Reported-by: Farhan Ali <alifm@linux.ibm.com>
+with drain entirely, but couldn't find a way to do that. Instead, this
-Signed-off-by: Nishanth Aravamudan <naravamudan@digitalocean.com>
+patch accepts the fragile nature of the code and reorders it so that
-Reviewed-by: John Snow <jsnow@redhat.com>
+vblk->dataplane_started is false during drain operations. This way the
-Message-id: 20180718211256.29774-1-naravamudan@digitalocean.com
+virtio_blk_drained_begin() and virtio_blk_drained_end() calls don't
-Cc: Eric Blake <eblake@redhat.com>
+touch the host notifier. The result is that
-Cc: Kevin Wolf <kwolf@redhat.com>
+virtio_blk_data_plane_start() and virtio_blk_data_plane_stop() have
-Cc: John Snow <jsnow@redhat.com>
+complete control over the host notifier and stale file descriptors are
-Cc: Max Reitz <mreitz@redhat.com>
+no longer left in the AioContext.
-Cc: Stefan Hajnoczi <stefanha@redhat.com>
-Cc: Fam Zheng <famz@redhat.com>
+This patch fixes the 100% CPU consumption in the main loop thread and
-Cc: Paolo Bonzini <pbonzini@redhat.com>
+correctly moves host notifier processing to the IOThread.
-Cc: qemu-block@nongnu.org
-Cc: qemu-devel@nongnu.org
+Fixes: 1665d9326fd2 ("virtio-blk: implement BlockDevOps->drained_begin()")
 Reported-by: Lukáš Doktor <ldoktor@redhat.com>
 Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
 Tested-by: Lukas Doktor <ldoktor@redhat.com>
 Message-id: 20230704151527.193586-1-stefanha@redhat.com
 Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
 ---
- block/file-posix.c | 3 +++
+ hw/block/dataplane/virtio-blk.c | 67 +++++++++++++++++++--------------
-file changed, 3 insertions(+)
+file changed, 38 insertions(+), 29 deletions(-)
-diff --git a/block/file-posix.c b/block/file-posix.c
+diff --git a/hw/block/dataplane/virtio-blk.c b/hw/block/dataplane/virtio-blk.c
 index XXXXXXX..XXXXXXX 100644
---- a/block/file-posix.c
+--- a/hw/block/dataplane/virtio-blk.c
-+++ b/block/file-posix.c
++++ b/hw/block/dataplane/virtio-blk.c
-@@ -XXX,XX +XXX,XX @@ static BlockDriver bdrv_host_device = {
+@@ -XXX,XX +XXX,XX @@ int virtio_blk_data_plane_start(VirtIODevice *vdev)
-     .bdrv_refresh_limits = raw_refresh_limits,
-     .bdrv_io_plug = raw_aio_plug,
+     memory_region_transaction_commit();
-     .bdrv_io_unplug = raw_aio_unplug,
-+    .bdrv_attach_aio_context = raw_aio_attach_aio_context,
+-    /*
+-     * These fields are visible to the IOThread so we rely on implicit barriers
-     .bdrv_co_truncate       = raw_co_truncate,
+-     * in aio_context_acquire() on the write side and aio_notify_accept() on
-     .bdrv_getlength    = raw_getlength,
+-     * the read side.
-@@ -XXX,XX +XXX,XX @@ static BlockDriver bdrv_host_cdrom = {
+-     */
-     .bdrv_refresh_limits = raw_refresh_limits,
+-    s->starting = false;
-     .bdrv_io_plug = raw_aio_plug,
+-    vblk->dataplane_started = true;
-     .bdrv_io_unplug = raw_aio_unplug,
+     trace_virtio_blk_data_plane_start(s);
-+    .bdrv_attach_aio_context = raw_aio_attach_aio_context,
+     old_context = blk_get_aio_context(s->conf->conf.blk);
-     .bdrv_co_truncate    = raw_co_truncate,
+@@ -XXX,XX +XXX,XX @@ int virtio_blk_data_plane_start(VirtIODevice *vdev)
-     .bdrv_getlength      = raw_getlength,
+         event_notifier_set(virtio_queue_get_host_notifier(vq));
-@@ -XXX,XX +XXX,XX @@ static BlockDriver bdrv_host_cdrom = {
+     }
-     .bdrv_refresh_limits = raw_refresh_limits,
-     .bdrv_io_plug = raw_aio_plug,
++    /*
-     .bdrv_io_unplug = raw_aio_unplug,
++     * These fields must be visible to the IOThread when it processes the
-+    .bdrv_attach_aio_context = raw_aio_attach_aio_context,
++     * virtqueue, otherwise it will think dataplane has not started yet.
++     *
-     .bdrv_co_truncate    = raw_co_truncate,
++     * Make sure ->dataplane_started is false when blk_set_aio_context() is
-     .bdrv_getlength      = raw_getlength,
++     * called above so that draining does not cause the host notifier to be
 +     * detached/attached prematurely.
 +     */
 +    s->starting = false;
 +    vblk->dataplane_started = true;
 +    smp_wmb(); /* paired with aio_notify_accept() on the read side */
 +
      /* Get this show started by hooking up our callbacks */
      if (!blk_in_drain(s->conf->conf.blk)) {
          aio_context_acquire(s->ctx);
@@ -XXX,XX +XXX,XX @@ int virtio_blk_data_plane_start(VirtIODevice *vdev)
    fail_guest_notifiers:
      vblk->dataplane_disabled = true;
      s->starting = false;
 -    vblk->dataplane_started = true;
      return -ENOSYS;
  }
@@ -XXX,XX +XXX,XX @@ void virtio_blk_data_plane_stop(VirtIODevice *vdev)
          aio_wait_bh_oneshot(s->ctx, virtio_blk_data_plane_stop_bh, s);
      }
 +    /*
 +     * Batch all the host notifiers in a single transaction to avoid
 +     * quadratic time complexity in address_space_update_ioeventfds().
 +     */
 +    memory_region_transaction_begin();
 +
 +    for (i = 0; i < nvqs; i++) {
 +        virtio_bus_set_host_notifier(VIRTIO_BUS(qbus), i, false);
 +    }
 +
 +    /*
 +     * The transaction expects the ioeventfds to be open when it
 +     * commits. Do it now, before the cleanup loop.
 +     */
 +    memory_region_transaction_commit();
 +
 +    for (i = 0; i < nvqs; i++) {
 +        virtio_bus_cleanup_host_notifier(VIRTIO_BUS(qbus), i);
 +    }
 +
 +    /*
 +     * Set ->dataplane_started to false before draining so that host notifiers
 +     * are not detached/attached anymore.
 +     */
 +    vblk->dataplane_started = false;
 +
      aio_context_acquire(s->ctx);
      /* Wait for virtio_blk_dma_restart_bh() and in flight I/O to complete */
@@ -XXX,XX +XXX,XX @@ void virtio_blk_data_plane_stop(VirtIODevice *vdev)
      aio_context_release(s->ctx);
 -    /*
 -     * Batch all the host notifiers in a single transaction to avoid
 -     * quadratic time complexity in address_space_update_ioeventfds().
 -     */
 -    memory_region_transaction_begin();
 -
 -    for (i = 0; i < nvqs; i++) {
 -        virtio_bus_set_host_notifier(VIRTIO_BUS(qbus), i, false);
 -    }
 -
 -    /*
 -     * The transaction expects the ioeventfds to be open when it
 -     * commits. Do it now, before the cleanup loop.
 -     */
 -    memory_region_transaction_commit();
 -
 -    for (i = 0; i < nvqs; i++) {
 -        virtio_bus_cleanup_host_notifier(VIRTIO_BUS(qbus), i);
 -    }
 -
      qemu_bh_cancel(s->bh);
      notify_guest_bh(s); /* final chance to notify guest */
      /* Clean up guest notifier (irq) */
      k->set_guest_notifiers(qbus->parent, nvqs, false);
 -    vblk->dataplane_started = false;
      s->stopping = false;
  }
 --
-.17.1
+.40.1

From: Nishanth Aravamudan <naravamudan@digitalocean.com>

In ed6e2161 ("linux-aio: properly bubble up errors from initialzation"),
I only added a bdrv_attach_aio_context callback for the bdrv_file
driver. There are several other drivers that use the shared
aio_plug callback, though, and they will trip the assertion added to
aio_get_linux_aio because they did not call aio_setup_linux_aio first.
Add the appropriate callback definition to the affected driver
definitions.

Fixes: ed6e2161 ("linux-aio: properly bubble up errors from initialization")
Reported-by: Farhan Ali <alifm@linux.ibm.com>
Signed-off-by: Nishanth Aravamudan <naravamudan@digitalocean.com>
Reviewed-by: John Snow <jsnow@redhat.com>
Message-id: 20180718211256.29774-1-naravamudan@digitalocean.com
Cc: Eric Blake <eblake@redhat.com>
Cc: Kevin Wolf <kwolf@redhat.com>
Cc: John Snow <jsnow@redhat.com>
Cc: Max Reitz <mreitz@redhat.com>
Cc: Stefan Hajnoczi <stefanha@redhat.com>
Cc: Fam Zheng <famz@redhat.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: qemu-block@nongnu.org
Cc: qemu-devel@nongnu.org
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
---
 block/file-posix.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/block/file-posix.c b/block/file-posix.c
index XXXXXXX..XXXXXXX 100644
--- a/block/file-posix.c
+++ b/block/file-posix.c
@@ -XXX,XX +XXX,XX @@ static BlockDriver bdrv_host_device = {
     .bdrv_refresh_limits = raw_refresh_limits,
     .bdrv_io_plug = raw_aio_plug,
     .bdrv_io_unplug = raw_aio_unplug,
+    .bdrv_attach_aio_context = raw_aio_attach_aio_context,
 
     .bdrv_co_truncate       = raw_co_truncate,
     .bdrv_getlength	= raw_getlength,
@@ -XXX,XX +XXX,XX @@ static BlockDriver bdrv_host_cdrom = {
     .bdrv_refresh_limits = raw_refresh_limits,
     .bdrv_io_plug = raw_aio_plug,
     .bdrv_io_unplug = raw_aio_unplug,
+    .bdrv_attach_aio_context = raw_aio_attach_aio_context,
 
     .bdrv_co_truncate    = raw_co_truncate,
     .bdrv_getlength      = raw_getlength,
@@ -XXX,XX +XXX,XX @@ static BlockDriver bdrv_host_cdrom = {
     .bdrv_refresh_limits = raw_refresh_limits,
     .bdrv_io_plug = raw_aio_plug,
     .bdrv_io_unplug = raw_aio_unplug,
+    .bdrv_attach_aio_context = raw_aio_attach_aio_context,
 
     .bdrv_co_truncate    = raw_co_truncate,
     .bdrv_getlength      = raw_getlength,
-- 
2.17.1

The main loop thread can consume 100% CPU when using --device
virtio-blk-pci,iothread=<iothread>. ppoll() constantly returns but
reading virtqueue host notifiers fails with EAGAIN. The file descriptors
are stale and remain registered with the AioContext because of bugs in
the virtio-blk dataplane start/stop code.

The problem is that the dataplane start/stop code involves drain
operations, which call virtio_blk_drained_begin() and
virtio_blk_drained_end() at points where the host notifier is not
operational:
- In virtio_blk_data_plane_start(), blk_set_aio_context() drains after
  vblk->dataplane_started has been set to true but the host notifier has
  not been attached yet.
- In virtio_blk_data_plane_stop(), blk_drain() and blk_set_aio_context()
  drain after the host notifier has already been detached but with
  vblk->dataplane_started still set to true.

I would like to simplify ->ioeventfd_start/stop() to avoid interactions
with drain entirely, but couldn't find a way to do that. Instead, this
patch accepts the fragile nature of the code and reorders it so that
vblk->dataplane_started is false during drain operations. This way the
virtio_blk_drained_begin() and virtio_blk_drained_end() calls don't
touch the host notifier. The result is that
virtio_blk_data_plane_start() and virtio_blk_data_plane_stop() have
complete control over the host notifier and stale file descriptors are
no longer left in the AioContext.

This patch fixes the 100% CPU consumption in the main loop thread and
correctly moves host notifier processing to the IOThread.

Fixes: 1665d9326fd2 ("virtio-blk: implement BlockDevOps->drained_begin()")
Reported-by: Lukáš Doktor <ldoktor@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Tested-by: Lukas Doktor <ldoktor@redhat.com>
Message-id: 20230704151527.193586-1-stefanha@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
---
 hw/block/dataplane/virtio-blk.c | 67 +++++++++++++++++++--------------
 1 file changed, 38 insertions(+), 29 deletions(-)

diff --git a/hw/block/dataplane/virtio-blk.c b/hw/block/dataplane/virtio-blk.c
index XXXXXXX..XXXXXXX 100644
--- a/hw/block/dataplane/virtio-blk.c
+++ b/hw/block/dataplane/virtio-blk.c
@@ -XXX,XX +XXX,XX @@ int virtio_blk_data_plane_start(VirtIODevice *vdev)
 
     memory_region_transaction_commit();
 
-    /*
-     * These fields are visible to the IOThread so we rely on implicit barriers
-     * in aio_context_acquire() on the write side and aio_notify_accept() on
-     * the read side.
-     */
-    s->starting = false;
-    vblk->dataplane_started = true;
     trace_virtio_blk_data_plane_start(s);
 
     old_context = blk_get_aio_context(s->conf->conf.blk);
@@ -XXX,XX +XXX,XX @@ int virtio_blk_data_plane_start(VirtIODevice *vdev)
         event_notifier_set(virtio_queue_get_host_notifier(vq));
     }
 
+    /*
+     * These fields must be visible to the IOThread when it processes the
+     * virtqueue, otherwise it will think dataplane has not started yet.
+     *
+     * Make sure ->dataplane_started is false when blk_set_aio_context() is
+     * called above so that draining does not cause the host notifier to be
+     * detached/attached prematurely.
+     */
+    s->starting = false;
+    vblk->dataplane_started = true;
+    smp_wmb(); /* paired with aio_notify_accept() on the read side */
+
     /* Get this show started by hooking up our callbacks */
     if (!blk_in_drain(s->conf->conf.blk)) {
         aio_context_acquire(s->ctx);
@@ -XXX,XX +XXX,XX @@ int virtio_blk_data_plane_start(VirtIODevice *vdev)
   fail_guest_notifiers:
     vblk->dataplane_disabled = true;
     s->starting = false;
-    vblk->dataplane_started = true;
     return -ENOSYS;
 }
 
@@ -XXX,XX +XXX,XX @@ void virtio_blk_data_plane_stop(VirtIODevice *vdev)
         aio_wait_bh_oneshot(s->ctx, virtio_blk_data_plane_stop_bh, s);
     }
 
+    /*
+     * Batch all the host notifiers in a single transaction to avoid
+     * quadratic time complexity in address_space_update_ioeventfds().
+     */
+    memory_region_transaction_begin();
+
+    for (i = 0; i < nvqs; i++) {
+        virtio_bus_set_host_notifier(VIRTIO_BUS(qbus), i, false);
+    }
+
+    /*
+     * The transaction expects the ioeventfds to be open when it
+     * commits. Do it now, before the cleanup loop.
+     */
+    memory_region_transaction_commit();
+
+    for (i = 0; i < nvqs; i++) {
+        virtio_bus_cleanup_host_notifier(VIRTIO_BUS(qbus), i);
+    }
+
+    /*
+     * Set ->dataplane_started to false before draining so that host notifiers
+     * are not detached/attached anymore.
+     */
+    vblk->dataplane_started = false;
+
     aio_context_acquire(s->ctx);
 
     /* Wait for virtio_blk_dma_restart_bh() and in flight I/O to complete */
@@ -XXX,XX +XXX,XX @@ void virtio_blk_data_plane_stop(VirtIODevice *vdev)
 
     aio_context_release(s->ctx);
 
-    /*
-     * Batch all the host notifiers in a single transaction to avoid
-     * quadratic time complexity in address_space_update_ioeventfds().
-     */
-    memory_region_transaction_begin();
-
-    for (i = 0; i < nvqs; i++) {
-        virtio_bus_set_host_notifier(VIRTIO_BUS(qbus), i, false);
-    }
-
-    /*
-     * The transaction expects the ioeventfds to be open when it
-     * commits. Do it now, before the cleanup loop.
-     */
-    memory_region_transaction_commit();
-
-    for (i = 0; i < nvqs; i++) {
-        virtio_bus_cleanup_host_notifier(VIRTIO_BUS(qbus), i);
-    }
-
     qemu_bh_cancel(s->bh);
     notify_guest_bh(s); /* final chance to notify guest */
 
     /* Clean up guest notifier (irq) */
     k->set_guest_notifiers(qbus->parent, nvqs, false);
 
-    vblk->dataplane_started = false;
     s->stopping = false;
 }
-- 
2.40.1