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[Qemu-block] [PATCH for-2.9 3/5] block: Quiesce old aio context during b


From: Fam Zheng
Subject: [Qemu-block] [PATCH for-2.9 3/5] block: Quiesce old aio context during bdrv_set_aio_context
Date: Thu, 6 Apr 2017 22:25:25 +0800

The fact that the bs->aio_context is changing can confuse the dataplane
iothread, because of the now fine granularity aio context lock.
bdrv_drain should rather be a bdrv_drained_begin/end pair, but since
bs->aio_context is changing, we can just use aio_disable_external and
block_job_pause.

Reported-by: Ed Swierk <address@hidden>
Signed-off-by: Fam Zheng <address@hidden>
---
 block.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/block.c b/block.c
index 8893ac1..e70684a 100644
--- a/block.c
+++ b/block.c
@@ -4395,11 +4395,14 @@ void bdrv_attach_aio_context(BlockDriverState *bs,
 
 void bdrv_set_aio_context(BlockDriverState *bs, AioContext *new_context)
 {
-    AioContext *ctx;
+    AioContext *ctx = bdrv_get_aio_context(bs);
 
+    aio_disable_external(ctx);
+    if (bs->job) {
+        block_job_pause(bs->job);
+    }
     bdrv_drain(bs); /* ensure there are no in-flight requests */
 
-    ctx = bdrv_get_aio_context(bs);
     while (aio_poll(ctx, false)) {
         /* wait for all bottom halves to execute */
     }
@@ -4412,6 +4415,10 @@ void bdrv_set_aio_context(BlockDriverState *bs, 
AioContext *new_context)
     aio_context_acquire(new_context);
     bdrv_attach_aio_context(bs, new_context);
     aio_context_release(new_context);
+    if (bs->job) {
+        block_job_resume(bs->job);
+    }
+    aio_enable_external(ctx);
 }
 
 void bdrv_add_aio_context_notifier(BlockDriverState *bs,
-- 
2.9.3




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