linux-kernel - Re: blkdev_issue_discard() hangs forever if the underlying storage device is removed

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Message-ID: <alpine.LFD.2.00.1108291712590.3904@dhcp-27-109.brq.redhat.com>
Date:	Mon, 29 Aug 2011 17:16:06 +0200 (CEST)
From:	Lukas Czerner <lczerner@...hat.com>
To:	Lin Ming <lxy@...pku.edu.cn>
cc:	Lukas Czerner <lczerner@...hat.com>,
	Bart Van Assche <bvanassche@....org>,
	Jens Axboe <jaxboe@...ionio.com>,
	Mike Snitzer <snitzer@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: blkdev_issue_discard() hangs forever if the underlying storage
 device is removed

On Mon, 29 Aug 2011, Lin Ming wrote:

> On Mon, Aug 29, 2011 at 10:42 PM, Lukas Czerner <lczerner@...hat.com> wrote:
> > On Mon, 29 Aug 2011, Lin Ming wrote:
> >
> >> On Mon, Aug 29, 2011 at 7:56 PM, Lukas Czerner <lczerner@...hat.com> wrote:
> >> >
> >> > Regarding the atomic operations I do not think that implicit memory
> >> > barriers are needed here as atomic_dec_and_test() implies memory
> >>
> >> Which implicit memory barrier you are talking about?
> >
> > smp_mb() at both side of the operation as documented here in
> > Documentation/memory-barriers.txt
> 
> Thanks for the info.
> 
> But I don't follow you ... why that implicit memory barriers are NOT needed?
> 

Oh, I am sorry I have actually wanted to say that *explicit* memory
barriers are no needed in that case. Sorry for the confusion!

Thanks!
-Lukas
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