[PATCH 0/2] block: Fix crash in blockdev-reopen with iothreads

[PATCH 0/2] block: Fix crash in blockdev-reopen with iothreads

[Kevin Wolf]

Kevin Wolf (2):
  block: Lock AioContext for drain_end in blockdev-reopen
  iotests: Test blockdev-reopen with iothreads and throttling

 blockdev.c                 | 11 ++++++++++-
 tests/qemu-iotests/245     | 36 +++++++++++++++++++++++++++++++++---
 tests/qemu-iotests/245.out |  4 ++--
 3 files changed, 45 insertions(+), 6 deletions(-)

-- 
2.31.1

[PATCH 1/2] block: Lock AioContext for drain_end in blockdev-reopen

[Kevin Wolf]

bdrv_subtree_drained_end() requires the caller to hold the AioContext
lock for the drained node. Not doing this for nodes outside of the main
AioContext leads to crashes when AIO_WAIT_WHILE() needs to wait and
tries to temporarily release the lock.

Fixes: 3908b7a8994fa5ef7a89aa58cd5a02fc58141592
Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=2046659
Reported-by: Qing Wang <qinwang@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
---
 blockdev.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/blockdev.c b/blockdev.c
index 8197165bb5..42e098b458 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -3530,6 +3530,7 @@ void qmp_blockdev_reopen(BlockdevOptionsList *reopen_list, Error **errp)
 {
     BlockReopenQueue *queue = NULL;
     GSList *drained = NULL;
+    GSList *p;
 
     /* Add each one of the BDS that we want to reopen to the queue */
     for (; reopen_list != NULL; reopen_list = reopen_list->next) {
@@ -3579,7 +3580,15 @@ void qmp_blockdev_reopen(BlockdevOptionsList *reopen_list, Error **errp)
 
 fail:
     bdrv_reopen_queue_free(queue);
-    g_slist_free_full(drained, (GDestroyNotify) bdrv_subtree_drained_end);
+    for (p = drained; p; p = p->next) {
+        BlockDriverState *bs = p->data;
+        AioContext *ctx = bdrv_get_aio_context(bs);
+
+        aio_context_acquire(ctx);
+        bdrv_subtree_drained_end(bs);
+        aio_context_release(ctx);
+    }
+    g_slist_free(drained);
 }
 
 void qmp_blockdev_del(const char *node_name, Error **errp)
-- 
2.31.1

[PATCH 2/2] iotests: Test blockdev-reopen with iothreads and throttling

[Kevin Wolf]

The 'throttle' block driver implements .bdrv_co_drain_end, so
blockdev-reopen will have to wait for it to complete in the polling
loop at the end of qmp_blockdev_reopen(). This makes AIO_WAIT_WHILE()
release the AioContext lock, which causes a crash if the lock hasn't
correctly been taken.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
---
 tests/qemu-iotests/245     | 36 +++++++++++++++++++++++++++++++++---
 tests/qemu-iotests/245.out |  4 ++--
 2 files changed, 35 insertions(+), 5 deletions(-)

diff --git a/tests/qemu-iotests/245 b/tests/qemu-iotests/245
index 24ac43f70e..8cbed7821b 100755
--- a/tests/qemu-iotests/245
+++ b/tests/qemu-iotests/245
@@ -1138,12 +1138,13 @@ class TestBlockdevReopen(iotests.QMPTestCase):
         self.assertEqual(self.get_node('hd1'), None)
         self.assert_qmp(self.get_node('hd2'), 'ro', True)
 
-    def run_test_iothreads(self, iothread_a, iothread_b, errmsg = None):
-        opts = hd_opts(0)
+    def run_test_iothreads(self, iothread_a, iothread_b, errmsg = None,
+                           opts_a = None, opts_b = None):
+        opts = opts_a or hd_opts(0)
         result = self.vm.qmp('blockdev-add', conv_keys = False, **opts)
         self.assert_qmp(result, 'return', {})
 
-        opts2 = hd_opts(2)
+        opts2 = opts_b or hd_opts(2)
         result = self.vm.qmp('blockdev-add', conv_keys = False, **opts2)
         self.assert_qmp(result, 'return', {})
 
@@ -1194,6 +1195,35 @@ class TestBlockdevReopen(iotests.QMPTestCase):
     def test_iothreads_switch_overlay(self):
         self.run_test_iothreads('', 'iothread0')
 
+    def test_iothreads_with_throttling(self):
+        # Create a throttle-group object
+        opts = { 'qom-type': 'throttle-group', 'id': 'group0',
+                 'limits': { 'iops-total': 1000 } }
+        result = self.vm.qmp('object-add', conv_keys = False, **opts)
+        self.assert_qmp(result, 'return', {})
+
+        # Options with a throttle filter between format and protocol
+        opts = [
+            {
+                'driver': iotests.imgfmt,
+                'node-name': f'hd{idx}',
+                'file' : {
+                    'node-name': f'hd{idx}-throttle',
+                    'driver': 'throttle',
+                    'throttle-group': 'group0',
+                    'file': {
+                        'driver': 'file',
+                        'node-name': f'hd{idx}-file',
+                        'filename': hd_path[idx],
+                    },
+                },
+            }
+            for idx in (0, 2)
+        ]
+
+        self.run_test_iothreads('iothread0', 'iothread0', None,
+                                opts[0], opts[1])
+
 if __name__ == '__main__':
     iotests.activate_logging()
     iotests.main(supported_fmts=["qcow2"],
diff --git a/tests/qemu-iotests/245.out b/tests/qemu-iotests/245.out
index 4eced19294..a4e04a3266 100644
--- a/tests/qemu-iotests/245.out
+++ b/tests/qemu-iotests/245.out
@@ -17,8 +17,8 @@ read 1/1 bytes at offset 262152
 read 1/1 bytes at offset 262160
 1 bytes, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
 
-...............
+................
 ----------------------------------------------------------------------
-Ran 25 tests
+Ran 26 tests
 
 OK
-- 
2.31.1

Re: [PATCH 1/2] block: Lock AioContext for drain_end in blockdev-reopen

[Hanna Reitz]

On 03.02.22 15:05, Kevin Wolf wrote:
> bdrv_subtree_drained_end() requires the caller to hold the AioContext
> lock for the drained node. Not doing this for nodes outside of the main
> AioContext leads to crashes when AIO_WAIT_WHILE() needs to wait and
> tries to temporarily release the lock.
>
> Fixes: 3908b7a8994fa5ef7a89aa58cd5a02fc58141592
> Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=2046659
> Reported-by: Qing Wang <qinwang@redhat.com>
> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
> ---
>   blockdev.c | 11 ++++++++++-
>   1 file changed, 10 insertions(+), 1 deletion(-)

Reviewed-by: Hanna Reitz <hreitz@redhat.com>

Re: [PATCH 2/2] iotests: Test blockdev-reopen with iothreads and throttling

[Hanna Reitz]

On 03.02.22 15:05, Kevin Wolf wrote:
> The 'throttle' block driver implements .bdrv_co_drain_end, so
> blockdev-reopen will have to wait for it to complete in the polling
> loop at the end of qmp_blockdev_reopen(). This makes AIO_WAIT_WHILE()
> release the AioContext lock, which causes a crash if the lock hasn't
> correctly been taken.
>
> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
> ---
>   tests/qemu-iotests/245     | 36 +++++++++++++++++++++++++++++++++---
>   tests/qemu-iotests/245.out |  4 ++--
>   2 files changed, 35 insertions(+), 5 deletions(-)

Reviewed-by: Hanna Reitz <hreitz@redhat.com>