[Qemu-devel] [PATCH 01/10] migration: add missed aio_context_acquire for state writing/reading

["Denis V. Lunev" <den@openvz.org>]

aio_context should be locked in the similar way as was done in QMP
snapshot creation in the other case there are a lot of possible
troubles if native AIO mode is enabled for disk.

qemu_fopen_bdrv and bdrv_fclose are used in real snapshot operations only
along with block drivers. This change should influence only HMP snapshot
operations.

AioContext lock is reqursive. Thus nested locking should not be a problem.

Signed-off-by: Denis V. Lunev <den@openvz.org>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Juan Quintela <quintela@redhat.com>
CC: Stefan Hajnoczi <stefanha@redhat.com>
CC: Amit Shah <amit.shah@redhat.com>
---
 migration/savevm.c | 18 +++++++++++++++---
 1 file changed, 15 insertions(+), 3 deletions(-)

diff --git a/migration/savevm.c b/migration/savevm.c
index dbcc39a..1653f56 100644
--- a/migration/savevm.c
+++ b/migration/savevm.c
@@ -153,7 +153,11 @@ static ssize_t block_get_buffer(void *opaque, uint8_t *buf, int64_t pos,
 
 static int bdrv_fclose(void *opaque)
 {
-    return bdrv_flush(opaque);
+    BlockDriverState *bs = (BlockDriverState *)opaque;
+    int ret = bdrv_flush(bs);
+
+    aio_context_release(bdrv_get_aio_context(bs));
+    return ret;
 }
 
 static const QEMUFileOps bdrv_read_ops = {
@@ -169,10 +173,18 @@ static const QEMUFileOps bdrv_write_ops = {
 
 static QEMUFile *qemu_fopen_bdrv(BlockDriverState *bs, int is_writable)
 {
+    QEMUFile *file;
+
     if (is_writable) {
-        return qemu_fopen_ops(bs, &bdrv_write_ops);
+        file = qemu_fopen_ops(bs, &bdrv_write_ops);
+    } else {
+        file = qemu_fopen_ops(bs, &bdrv_read_ops);
+    }
+
+    if (file != NULL) {
+        aio_context_acquire(bdrv_get_aio_context(bs));
     }
-    return qemu_fopen_ops(bs, &bdrv_read_ops);
+    return file;
 }
 
 
-- 
2.5.0