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[Qemu-devel] [PULL 02/15] block: Forbid bdrv_set_aio_context outside BQL
From: |
Paolo Bonzini |
Subject: |
[Qemu-devel] [PULL 02/15] block: Forbid bdrv_set_aio_context outside BQL |
Date: |
Mon, 2 Mar 2015 11:08:41 +0100 |
From: Fam Zheng <address@hidden>
Even if the caller has both the old and the new AioContext's, there can
be a deadlock, due to the leading bdrv_drain_all.
Suppose there are four io threads (A, B, A0, B0) with A and B owning a
BDS for each (bs_a, bs_b); Now A wants to move bs_a to iothread A0, and
B wants to move bs_b to B0, at the same time:
iothread A iothread B
--------------------------------------------------------------------------
aio_context_acquire(A0) /* OK */ aio_context_acquire(B0) /* OK */
bdrv_set_aio_context(bs_a, A0) bdrv_set_aio_context(bs_b, B0)
-> bdrv_drain_all() -> bdrv_drain_all()
-> acquire A /* OK */ -> acquire A /* blocked */
-> acquire B /* blocked */ -> acquire B
... ...
Deadlock happens because A is waiting for B, and B is waiting for A.
Signed-off-by: Fam Zheng <address@hidden>
Reviewed-by: Paolo Bonzini <address@hidden>
Message-Id: <address@hidden>
Signed-off-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 471d11d..649c269 100644
--- a/include/block/block.h
+++ b/include/block/block.h
@@ -547,8 +547,7 @@ 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);
--
2.3.0
- [Qemu-devel] [PULL 00/15] Misc changes for 2015-03-02, Paolo Bonzini, 2015/03/02
- [Qemu-devel] [PULL 02/15] block: Forbid bdrv_set_aio_context outside BQL,
Paolo Bonzini <=
- [Qemu-devel] [PULL 03/15] virtio-scsi-dataplane: Call blk_set_aio_context within BQL, Paolo Bonzini, 2015/03/02
- [Qemu-devel] [PULL 04/15] timer: replace time() with QEMU_CLOCK_HOST, Paolo Bonzini, 2015/03/02
- [Qemu-devel] [PULL 05/15] bootdevice: fix segment fault when booting guest with '-kernel' and '-initrd', Paolo Bonzini, 2015/03/02
- [Qemu-devel] [PULL 06/15] Add specific config options for PCI-E bridges, Paolo Bonzini, 2015/03/02
- [Qemu-devel] [PULL 07/15] Create specific config option for "platform-bus", Paolo Bonzini, 2015/03/02
- [Qemu-devel] [PULL 08/15] Give ivshmem its own config option, Paolo Bonzini, 2015/03/02
- [Qemu-devel] [PULL 01/15] scsi: give device a parent before setting properties, Paolo Bonzini, 2015/03/02
- [Qemu-devel] [PULL 09/15] iscsi: Handle write protected case in reopen, Paolo Bonzini, 2015/03/02
- [Qemu-devel] [PULL 13/15] virtio-scsi: Allocate op blocker reason before blocking, Paolo Bonzini, 2015/03/02
- [Qemu-devel] [PULL 10/15] Makefile: fix up parallel building under MSYS+MinGW, Paolo Bonzini, 2015/03/02