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Date: Mon, 10 Dec 2018 13:25:17 +0100
From: Kevin Wolf <kwolf@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH] blk: postpone request execution on a
 context protected with "drained section"
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To: Denis Plotnikov <dplotnikov@virtuozzo.com>
Cc: "keith.busch@intel.com" <keith.busch@intel.com>, "jsnow@redhat.com" <jsnow@redhat.com>, "qemu-block@nongnu.org" <qemu-block@nongnu.org>, "qemu-devel@nongnu.org" <qemu-devel@nongnu.org>, "mreitz@redhat.com" <mreitz@redhat.com>, "stefanha@redhat.com" <stefanha@redhat.com>, Denis Lunev <den@virtuozzo.com>, "famz@redhat.com" <famz@redhat.com>, Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>

Am 10.12.2018 um 13:14 hat Denis Plotnikov geschrieben:
> >> @@ -491,9 +506,17 @@ int64_t aio_compute_timeout(AioContext *ctx);
> >>    */
> >>   static inline void aio_disable_external(AioContext *ctx)
> >>   {
> >> +    aio_context_acquire(ctx);
> >>       atomic_inc(&ctx->external_disable_cnt);
> >> +    aio_context_release(ctx);
> >>   }
> > 
> > This acquire/release pair looks rather useless?
> 
> I'm not sure that I understand everything correctly...
> but can a thread (context) try to disable external in another context?

Yes, that can happen. For example, think of bdrv_drain_all().

Kevin