[Qemu-devel] [PATCH 1/3] block: Check for inserted BlockDriverState in blk_io_limits_disable()

[Alberto Garcia]

When you set I/O limits using block_set_io_throttle or the command
line throttling.* options they are kept in the BlockBackend regardless
of whether a BlockDriverState is attached to the backend or not.

Therefore when removing the limits using blk_io_limits_disable() we
need to check if there's a BDS before attempting to drain it, else it
will crash QEMU. This can be reproduced very easily using HMP:

     (qemu) drive_add 0 if=none,throttling.iops-total=5000
     (qemu) drive_del none0

Reported-by: sochin jiang <address@hidden>
Signed-off-by: Alberto Garcia <address@hidden>
---
 block/block-backend.c | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/block/block-backend.c b/block/block-backend.c
index 18e543780d..193a080096 100644
--- a/block/block-backend.c
+++ b/block/block-backend.c
@@ -1978,10 +1978,16 @@ void blk_set_io_limits(BlockBackend *blk, 
ThrottleConfig *cfg)
 
 void blk_io_limits_disable(BlockBackend *blk)
 {
-    assert(blk->public.throttle_group_member.throttle_state);
-    bdrv_drained_begin(blk_bs(blk));
-    throttle_group_unregister_tgm(&blk->public.throttle_group_member);
-    bdrv_drained_end(blk_bs(blk));
+    BlockDriverState *bs = blk_bs(blk);
+    ThrottleGroupMember *tgm = &blk->public.throttle_group_member;
+    assert(tgm->throttle_state);
+    if (bs) {
+        bdrv_drained_begin(bs);
+    }
+    throttle_group_unregister_tgm(tgm);
+    if (bs) {
+        bdrv_drained_end(bs);
+    }
 }
 
 /* should be called before blk_set_io_limits if a limit is set */
-- 
2.11.0