From 75d33e852536361367c8460abd8b04e3fe9921ee Mon Sep 17 00:00:00 2001 From: Stefan Hajnoczi Date: Tue, 16 May 2023 15:02:23 -0400 Subject: util/vhost-user-server: rename refcount to in_flight counter MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit The VuServer object has a refcount field and ref/unref APIs. The name is confusing because it's actually an in-flight request counter instead of a refcount. Normally a refcount destroys the object upon reaching zero. The VuServer counter is used to wake up the vhost-user coroutine when there are no more requests. Avoid confusing by renaming refcount and ref/unref to in_flight and inc/dec. Reviewed-by: Paolo Bonzini Reviewed-by: Philippe Mathieu-Daudé Signed-off-by: Stefan Hajnoczi Reviewed-by: Kevin Wolf Message-Id: <20230516190238.8401-6-stefanha@redhat.com> Signed-off-by: Kevin Wolf --- include/qemu/vhost-user-server.h | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) (limited to 'include/qemu') diff --git a/include/qemu/vhost-user-server.h b/include/qemu/vhost-user-server.h index 25c7243..bc0ac9d 100644 --- a/include/qemu/vhost-user-server.h +++ b/include/qemu/vhost-user-server.h @@ -41,7 +41,7 @@ typedef struct { const VuDevIface *vu_iface; /* Protected by ctx lock */ - unsigned int refcount; + unsigned int in_flight; bool wait_idle; VuDev vu_dev; QIOChannel *ioc; /* The I/O channel with the client */ @@ -60,8 +60,8 @@ bool vhost_user_server_start(VuServer *server, void vhost_user_server_stop(VuServer *server); -void vhost_user_server_ref(VuServer *server); -void vhost_user_server_unref(VuServer *server); +void vhost_user_server_inc_in_flight(VuServer *server); +void vhost_user_server_dec_in_flight(VuServer *server); void vhost_user_server_attach_aio_context(VuServer *server, AioContext *ctx); void vhost_user_server_detach_aio_context(VuServer *server); -- cgit v1.1 From 8f5e9a8ee189b44ffa90cc6db61e25499b9d786a Mon Sep 17 00:00:00 2001 From: Stefan Hajnoczi Date: Tue, 16 May 2023 15:02:24 -0400 Subject: block/export: wait for vhost-user-blk requests when draining Each vhost-user-blk request runs in a coroutine. When the BlockBackend enters a drained section we need to enter a quiescent state. Currently any in-flight requests race with bdrv_drained_begin() because it is unaware of vhost-user-blk requests. When blk_co_preadv/pwritev()/etc returns it wakes the bdrv_drained_begin() thread but vhost-user-blk request processing has not yet finished. The request coroutine continues executing while the main loop thread thinks it is in a drained section. One example where this is unsafe is for blk_set_aio_context() where bdrv_drained_begin() is called before .aio_context_detached() and .aio_context_attach(). If request coroutines are still running after bdrv_drained_begin(), then the AioContext could change underneath them and they race with new requests processed in the new AioContext. This could lead to virtqueue corruption, for example. (This example is theoretical, I came across this while reading the code and have not tried to reproduce it.) It's easy to make bdrv_drained_begin() wait for in-flight requests: add a .drained_poll() callback that checks the VuServer's in-flight counter. VuServer just needs an API that returns true when there are requests in flight. The in-flight counter needs to be atomic. Signed-off-by: Stefan Hajnoczi Reviewed-by: Kevin Wolf Message-Id: <20230516190238.8401-7-stefanha@redhat.com> Signed-off-by: Kevin Wolf --- include/qemu/vhost-user-server.h | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) (limited to 'include/qemu') diff --git a/include/qemu/vhost-user-server.h b/include/qemu/vhost-user-server.h index bc0ac9d..b1c1cda 100644 --- a/include/qemu/vhost-user-server.h +++ b/include/qemu/vhost-user-server.h @@ -40,8 +40,9 @@ typedef struct { int max_queues; const VuDevIface *vu_iface; + unsigned int in_flight; /* atomic */ + /* Protected by ctx lock */ - unsigned int in_flight; bool wait_idle; VuDev vu_dev; QIOChannel *ioc; /* The I/O channel with the client */ @@ -62,6 +63,7 @@ void vhost_user_server_stop(VuServer *server); void vhost_user_server_inc_in_flight(VuServer *server); void vhost_user_server_dec_in_flight(VuServer *server); +bool vhost_user_server_has_in_flight(VuServer *server); void vhost_user_server_attach_aio_context(VuServer *server, AioContext *ctx); void vhost_user_server_detach_aio_context(VuServer *server); -- cgit v1.1