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Re: [Qemu-devel] [PATCH 1/3] block: Forbid bdrv_set_aio_context outside
From: |
Paolo Bonzini |
Subject: |
Re: [Qemu-devel] [PATCH 1/3] block: Forbid bdrv_set_aio_context outside BQL |
Date: |
Fri, 13 Feb 2015 14:10:01 +0100 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.4.0 |
On 12/02/2015 06:21, Fam Zheng wrote:
> 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>
> ---
> 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);
>
>
Reviewed-by: Paolo Bonzini <address@hidden>
- [Qemu-devel] [PATCH 0/3] virtio-scsi: Fix unsafe bdrv_set_aio_context calls, Fam Zheng, 2015/02/12
- [Qemu-devel] [PATCH 2/3] virtio-scsi: Deduplicate cmd queue handling code of dataplane, Fam Zheng, 2015/02/12
- [Qemu-devel] [PATCH 1/3] block: Forbid bdrv_set_aio_context outside BQL, Fam Zheng, 2015/02/12
- Re: [Qemu-devel] [PATCH 1/3] block: Forbid bdrv_set_aio_context outside BQL,
Paolo Bonzini <=
- [Qemu-devel] [PATCH 3/3] virtio-scsi-dataplane: Use main thread BH to set BDS' aio context, Fam Zheng, 2015/02/12
- Re: [Qemu-devel] [PATCH 3/3] virtio-scsi-dataplane: Use main thread BH to set BDS' aio context, Paolo Bonzini, 2015/02/12
- Re: [Qemu-devel] [PATCH 3/3] virtio-scsi-dataplane: Use main thread BH to set BDS' aio context, Fam Zheng, 2015/02/12
- Re: [Qemu-devel] [PATCH 3/3] virtio-scsi-dataplane: Use main thread BH to set BDS' aio context, Paolo Bonzini, 2015/02/13
- Re: [Qemu-devel] [PATCH 3/3] virtio-scsi-dataplane: Use main thread BH to set BDS' aio context, Fam Zheng, 2015/02/13
- Re: [Qemu-devel] [PATCH 3/3] virtio-scsi-dataplane: Use main thread BH to set BDS' aio context, Paolo Bonzini, 2015/02/13
- Re: [Qemu-devel] [PATCH 3/3] virtio-scsi-dataplane: Use main thread BH to set BDS' aio context, Fam Zheng, 2015/02/13
- Re: [Qemu-devel] [PATCH 3/3] virtio-scsi-dataplane: Use main thread BH to set BDS' aio context, Paolo Bonzini, 2015/02/13