[Qemu-devel] [PATCH v2 02/25] block: acquire AioContext in bdrv_*_all()

[Stefan Hajnoczi <stefanha@redhat.com>]

bdrv_close_all(), bdrv_commit_all(), bdrv_flush_all(),
bdrv_invalidate_cache_all(), and bdrv_clear_incoming_migration_all() are
called by main loop code and touch all BlockDriverState instances.

Some BlockDriverState instances may be running in another AioContext.
Make sure to acquire the AioContext before closing the BlockDriverState.

This will protect against race conditions once virtio-blk data-plane is
using the BlockDriverState from another AioContext event loop.

Note that this patch does not convert bdrv_drain_all() yet since that
conversion is non-trivial.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
---
 block.c | 24 +++++++++++++++++++++++-
 1 file changed, 23 insertions(+), 1 deletion(-)

diff --git a/block.c b/block.c
index 75e8fcc..2a72409 100644
--- a/block.c
+++ b/block.c
@@ -1777,7 +1777,11 @@ void bdrv_close_all(void)
     BlockDriverState *bs;
 
     QTAILQ_FOREACH(bs, &bdrv_states, device_list) {
+        AioContext *aio_context = bdrv_get_aio_context(bs);
+
+        aio_context_acquire(aio_context);
         bdrv_close(bs);
+        aio_context_release(aio_context);
     }
 }
 
@@ -2278,12 +2282,17 @@ int bdrv_commit_all(void)
     BlockDriverState *bs;
 
     QTAILQ_FOREACH(bs, &bdrv_states, device_list) {
+        AioContext *aio_context = bdrv_get_aio_context(bs);
+
+        aio_context_acquire(aio_context);
         if (bs->drv && bs->backing_hd) {
             int ret = bdrv_commit(bs);
             if (ret < 0) {
+                aio_context_release(aio_context);
                 return ret;
             }
         }
+        aio_context_release(aio_context);
     }
     return 0;
 }
@@ -3751,10 +3760,15 @@ int bdrv_flush_all(void)
     int result = 0;
 
     QTAILQ_FOREACH(bs, &bdrv_states, device_list) {
-        int ret = bdrv_flush(bs);
+        AioContext *aio_context = bdrv_get_aio_context(bs);
+        int ret;
+
+        aio_context_acquire(aio_context);
+        ret = bdrv_flush(bs);
         if (ret < 0 && !result) {
             result = ret;
         }
+        aio_context_release(aio_context);
     }
 
     return result;
@@ -4898,7 +4912,11 @@ void bdrv_invalidate_cache_all(Error **errp)
     Error *local_err = NULL;
 
     QTAILQ_FOREACH(bs, &bdrv_states, device_list) {
+        AioContext *aio_context = bdrv_get_aio_context(bs);
+
+        aio_context_acquire(aio_context);
         bdrv_invalidate_cache(bs, &local_err);
+        aio_context_release(aio_context);
         if (local_err) {
             error_propagate(errp, local_err);
             return;
@@ -4911,7 +4929,11 @@ void bdrv_clear_incoming_migration_all(void)
     BlockDriverState *bs;
 
     QTAILQ_FOREACH(bs, &bdrv_states, device_list) {
+        AioContext *aio_context = bdrv_get_aio_context(bs);
+
+        aio_context_acquire(aio_context);
         bs->open_flags = bs->open_flags & ~(BDRV_O_INCOMING);
+        aio_context_release(aio_context);
     }
 }
 
-- 
1.9.0