From 59f0fc4b8011298bc542eb23cca385d83d1963cd Mon Sep 17 00:00:00 2001

From: Kevin Wolf <kwolf@redhat.com>

Date: Wed, 10 Oct 2018 20:22:02 +0100

Subject: [PATCH 36/49] block: Add missing locking in bdrv_co_drain_bh_cb()

RH-Author: Kevin Wolf <kwolf@redhat.com>

Message-id: <20181010202213.7372-24-kwolf@redhat.com>

Patchwork-id: 82613

O-Subject: [RHEL-8 qemu-kvm PATCH 33/44] block: Add missing locking in bdrv_co_drain_bh_cb()

Bugzilla: 1637976

RH-Acked-by: Max Reitz <mreitz@redhat.com>

RH-Acked-by: John Snow <jsnow@redhat.com>

RH-Acked-by: Thomas Huth <thuth@redhat.com>

bdrv_do_drained_begin/end() assume that they are called with the

AioContext lock of bs held. If we call drain functions from a coroutine

with the AioContext lock held, we yield and schedule a BH to move out of

coroutine context. This means that the lock for the home context of the

coroutine is released and must be re-acquired in the bottom half.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>

Reviewed-by: Max Reitz <mreitz@redhat.com>

(cherry picked from commit aa1361d54aac43094b98024b8b6c804eb6e41661)

Signed-off-by: Kevin Wolf <kwolf@redhat.com>

Signed-off-by: Danilo C. L. de Paula <ddepaula@redhat.com>

---

 block/io.c               | 15 +++++++++++++++

 include/qemu/coroutine.h |  5 +++++

 util/qemu-coroutine.c    |  5 +++++

 3 files changed, 25 insertions(+)

diff --git a/block/io.c b/block/io.c

index d404088..19db35e 100644

--- a/block/io.c

+++ b/block/io.c

@@ -286,6 +286,18 @@ static void bdrv_co_drain_bh_cb(void *opaque)

     BlockDriverState *bs = data->bs;

     if (bs) {

+        AioContext *ctx = bdrv_get_aio_context(bs);

+        AioContext *co_ctx = qemu_coroutine_get_aio_context(co);

+

+        /*

+         * When the coroutine yielded, the lock for its home context was

+         * released, so we need to re-acquire it here. If it explicitly

+         * acquired a different context, the lock is still held and we don't

+         * want to lock it a second time (or AIO_WAIT_WHILE() would hang).

+         */

+        if (ctx == co_ctx) {

+            aio_context_acquire(ctx);

+        }

         bdrv_dec_in_flight(bs);

         if (data->begin) {

             bdrv_do_drained_begin(bs, data->recursive, data->parent,

@@ -294,6 +306,9 @@ static void bdrv_co_drain_bh_cb(void *opaque)

             bdrv_do_drained_end(bs, data->recursive, data->parent,

                                 data->ignore_bds_parents);

         }

+        if (ctx == co_ctx) {

+            aio_context_release(ctx);

+        }

     } else {

         assert(data->begin);

         bdrv_drain_all_begin();

diff --git a/include/qemu/coroutine.h b/include/qemu/coroutine.h

index 6f8a487..9801e7f 100644

--- a/include/qemu/coroutine.h

+++ b/include/qemu/coroutine.h

@@ -90,6 +90,11 @@ void qemu_aio_coroutine_enter(AioContext *ctx, Coroutine *co);

 void coroutine_fn qemu_coroutine_yield(void);

 /**

+ * Get the AioContext of the given coroutine

+ */

+AioContext *coroutine_fn qemu_coroutine_get_aio_context(Coroutine *co);

+

+/**

  * Get the currently executing coroutine

  */

 Coroutine *coroutine_fn qemu_coroutine_self(void);

diff --git a/util/qemu-coroutine.c b/util/qemu-coroutine.c

index 1ba4191..2295928 100644

--- a/util/qemu-coroutine.c

+++ b/util/qemu-coroutine.c

@@ -198,3 +198,8 @@ bool qemu_coroutine_entered(Coroutine *co)

 {

     return co->caller;

 }

+

+AioContext *coroutine_fn qemu_coroutine_get_aio_context(Coroutine *co)

+{

+    return co->ctx;

+}

-- 

1.8.3.1