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[Qemu-devel] [PATCH v2 1/2] block: Forbid bdrv_set_aio_context outside B
From: |
Fam Zheng |
Subject: |
[Qemu-devel] [PATCH v2 1/2] block: Forbid bdrv_set_aio_context outside BQL |
Date: |
Sun, 15 Feb 2015 10:40:51 +0800 |
Even if the caller has the old #AioContext, there can be a deadlock, due
to the leading bdrv_drain_all:
Suppose there are three io threads (a, b, c) with each owning a BDS
(bds_a, bds_b, bds_c), and a and b want to move their own BDS to c at
the same time:
iothread a iothread b
--------------------------------------------------------------------------
bdrv_set_aio_context(bds_a, c) bdrv_set_aio_context(bds_b, c)
-> bdrv_drain_all() -> bdrv_drain_all()
-> acquire a (OK, already has) -> acquire a (blocked)
-> acquire b (blocked) -> acquire b
-> acquire c -> acquire c
Current caller of bdrv_set_aio_context outside BQL is
virtio-scsi-dataplane, which will be fixed in the next patches.
Signed-off-by: Fam Zheng <address@hidden>
Reviewed-by: Paolo Bonzini <address@hidden>
---
include/block/block.h | 3 +--
1 file changed, 1 insertion(+), 2 deletions(-)
diff --git a/include/block/block.h b/include/block/block.h
index 321295e..4fce25d 100644
--- a/include/block/block.h
+++ b/include/block/block.h
@@ -546,8 +546,7 @@ AioContext *bdrv_get_aio_context(BlockDriverState *bs);
* Changes the #AioContext used for fd handlers, timers, and BHs by this
* BlockDriverState and all its children.
*
- * This function must be called from the old #AioContext or with a lock held so
- * the old #AioContext is not executing.
+ * This function must be called with iothread lock held.
*/
void bdrv_set_aio_context(BlockDriverState *bs, AioContext *new_context);
--
2.1.0