[Qemu-block] [PATCH] throttle: fix a qemu crash problem when calling blk_delete

[sochin.jiang]

From: "sochin.jiang" <address@hidden>

commit 7ca7f0 moves the throttling related part of the BDS life cycle management
to BlockBackend, adds call to throttle_timers_detach_aio_context in 
blk_remove_bs.
commit 1606e remove a block device from its throttle group in blk_delete by 
calling
blk_io_limits_disable, this fix an easily reproducible qemu crash. But delete a
BB without a BDS inserted could easily cause a qemu crash too by calling
bdrv_drained_begin in blk_io_limits_disable. Say, a simply drive_add and then a
drive_del command.

Signed-off-by: sochin.jiang <address@hidden>
---
 block/io.c      | 8 ++++++++
 util/throttle.c | 6 +++---
 2 files changed, 11 insertions(+), 3 deletions(-)

diff --git a/block/io.c b/block/io.c
index 0854e0f..c411a87 100644
--- a/block/io.c
+++ b/block/io.c
@@ -269,6 +269,10 @@ static void coroutine_fn 
bdrv_co_yield_to_drain(BlockDriverState *bs,
 
 void bdrv_drained_begin(BlockDriverState *bs)
 {
+    if (!bs) {
+        return;
+    }
+
     if (qemu_in_coroutine()) {
         bdrv_co_yield_to_drain(bs, true);
         return;
@@ -284,6 +288,10 @@ void bdrv_drained_begin(BlockDriverState *bs)
 
 void bdrv_drained_end(BlockDriverState *bs)
 {
+    if (!bs) {
+        return;
+    }
+
     if (qemu_in_coroutine()) {
         bdrv_co_yield_to_drain(bs, false);
         return;
diff --git a/util/throttle.c b/util/throttle.c
index b38e742..35a21fc 100644
--- a/util/throttle.c
+++ b/util/throttle.c
@@ -245,8 +245,6 @@ void throttle_timers_init(ThrottleTimers *tt,
 /* destroy a timer */
 static void throttle_timer_destroy(QEMUTimer **timer)
 {
-    assert(*timer != NULL);
-
     timer_del(*timer);
     timer_free(*timer);
     *timer = NULL;
@@ -258,7 +256,9 @@ void throttle_timers_detach_aio_context(ThrottleTimers *tt)
     int i;
 
     for (i = 0; i < 2; i++) {
-        throttle_timer_destroy(&tt->timers[i]);
+        if (tt->timers[i]) {
+            throttle_timer_destroy(&tt->timers[i]);
+        }
     }
 }
 
-- 
1.8.3.1