[PULL,01/15] block: add missed aio_context_acquire into release_drive

Commit Message

Max Reitz April 3, 2017, 3:33 p.m. UTC

From: "Denis V. Lunev" <[e-mail]>

Recently we expirience hang with iothreads enabled with the following
call trace:
Thread 1 (Thread 0x7fa95efebc80 (LWP 177117)):
0  ppoll () from /lib64/libc.so.6
2  qemu_poll_ns () at qemu-timer.c:313
3  aio_poll () at aio-posix.c:457
4  bdrv_flush () at block/io.c:2641
5  bdrv_close () at block.c:2143
6  bdrv_delete () at block.c:2352
7  bdrv_unref () at block.c:3429
8  blk_remove_bs () at block/block-backend.c:427
9  blk_delete () at block/block-backend.c:178
10 blk_unref () at block/block-backend.c:226
11 object_property_del_all () at qom/object.c:399
12 object_finalize () at qom/object.c:461
13 object_unref () at qom/object.c:898
14 object_property_del_child () at qom/object.c:422
15 qmp_marshal_device_del () at qmp-marshal.c:1145
16 handle_qmp_command () at /usr/src/debug/qemu-2.6.0/monitor.c:3929

Technically bdrv_flush() stucks in
    while (rwco.ret == NOT_DONE) {
        aio_poll(aio_context, true);
    }
but rwco.ret is equal to 0 thus we have missed wakeup. Code investigation
reveals that we do not have performed aio_context_acquire() on this call
stack.

This patch adds missed lock.

Signed-off-by: Denis V. Lunev <[e-mail]>
CC: Kevin Wolf <[e-mail]>
CC: Max Reitz <[e-mail]>
CC: Eric Blake <[e-mail]>
CC: Markus Armbruster <[e-mail]>
Message-id: [e-mail]
Reviewed-by: Fam Zheng <[e-mail]>
Signed-off-by: Max Reitz <[e-mail]>
---
 hw/core/qdev-properties-system.c | 4 ++++
 1 file changed, 4 insertions(+)

Patch

diff --git a/hw/core/qdev-properties-system.c b/hw/core/qdev-properties-system.c
index c34be1c1ba..e885e650fb 100644
--- a/hw/core/qdev-properties-system.c
+++ b/hw/core/qdev-properties-system.c
@@ -124,8 +124,12 @@  static void release_drive(Object *obj, const char *name, void *opaque)
     BlockBackend **ptr = qdev_get_prop_ptr(dev, prop);
 
     if (*ptr) {
+        AioContext *ctx = blk_get_aio_context(*ptr);
+
+        aio_context_acquire(ctx);
         blockdev_auto_del(*ptr);
         blk_detach_dev(*ptr, dev);
+        aio_context_release(ctx);
     }
 }