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Re: [Qemu-devel] [PATCH v2 08/17] block: Add missing locking in bdrv_co_

From: Paolo Bonzini
Subject: Re: [Qemu-devel] [PATCH v2 08/17] block: Add missing locking in bdrv_co_drain_bh_cb()
Date: Thu, 13 Sep 2018 17:17:42 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1

On 13/09/2018 14:52, Kevin Wolf wrote:
> bdrv_do_drained_begin/end() assume that they are called with the
> AioContext lock of bs held. If we call drain functions from a coroutine
> with the AioContext lock held, we yield and schedule a BH to move out of
> coroutine context. This means that the lock for the home context of the
> coroutine is released and must be re-acquired in the bottom half.

What exactly needs the lock, is it bdrv_drain_invoke?

Would it make sense to always do release/acquire in bdrv_drain, and
always do acquire/release in bdrv_drain_invoke?  (Conditional locking is



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