From: Kevin Wolf <kwolf@redhat.com>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: qemu-devel@nongnu.org
Subject: Re: [Qemu-devel] [PATCH] dma: Avoid reentrancy in DMA transfer handlers
Date: Mon, 31 Oct 2011 17:00:44 +0100 [thread overview]
Message-ID: <4EAEC62C.9000600@redhat.com> (raw)
In-Reply-To: <j8mf6q$2gp$1@dough.gmane.org>
Am 31.10.2011 16:34, schrieb Paolo Bonzini:
> On 10/31/2011 03:46 PM, Kevin Wolf wrote:
>>> Hmm, I think you should set rearm = 1 to ensure the BH is run when
>>> ultimately you leave the sync read. Sorry for not spotting this before.
>>
>> I was about to agree, but in fact adding a rearm = 1; line leads to
>> crashes, whereas in the version I posted it just works. So it looks like
>> something is wrong with doing it, even though it seemed to make perfect
>> sense at the first sight.
>
> But what will restart the DMA at the end of the synchronous I/O, then?
bdrv_read/write are called inside fdctrl_read_data(), so the outer
DMA_run() already has rearm = 1.
I think the more interesting question is why rescheduling can break
anything. Where would we schedule the BH additionally when it isn't
already scheduled anyway?
Kevin
next prev parent reply other threads:[~2011-10-31 15:57 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-10-28 14:18 [Qemu-devel] [PATCH] dma: Avoid reentrancy in DMA transfer handlers Kevin Wolf
2011-10-28 16:35 ` Paolo Bonzini
2011-10-31 14:46 ` Kevin Wolf
2011-10-31 15:34 ` Paolo Bonzini
2011-10-31 16:00 ` Kevin Wolf [this message]
2011-10-31 16:40 ` Kevin Wolf
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