lists.openwall.net   lists  /  announce  owl-users  owl-dev  john-users  john-dev  passwdqc-users  yescrypt  popa3d-users  /  oss-security  kernel-hardening  musl  sabotage  tlsify  passwords  /  crypt-dev  xvendor  /  Bugtraq  Full-Disclosure  linux-kernel  linux-netdev  linux-ext4  linux-hardening  PHC 
Open Source and information security mailing list archives
 
Hash Suite: Windows password security audit tool. GUI, reports in PDF.
[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Date:	Thu, 20 Mar 2014 12:30:04 -0400
From:	Benjamin LaHaise <bcrl@...ck.org>
To:	Dave Jones <davej@...hat.com>, Gu Zheng <guz.fnst@...fujitsu.com>,
	Al Viro <viro@...iv.linux.org.uk>, jmoyer@...hat.com,
	kosaki.motohiro@...fujitsu.com,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>,
	tangchen <tangchen@...fujitsu.com>, miaox@...fujitsu.com,
	linux-aio@...ck.org, fsdevel <linux-fsdevel@...r.kernel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 2/2] aio: fix the confliction of read events and migrating ring page

On Thu, Mar 20, 2014 at 10:32:07AM -0400, Dave Jones wrote:
> On Thu, Mar 20, 2014 at 01:46:25PM +0800, Gu Zheng wrote:
> 
>  > diff --git a/fs/aio.c b/fs/aio.c
>  > index 88ad40c..e353085 100644
>  > --- a/fs/aio.c
>  > +++ b/fs/aio.c
>  > @@ -319,6 +319,9 @@ static int aio_migratepage(struct address_space *mapping, struct page *new,
>  >  	ctx->ring_pages[old->index] = new;
>  >  	spin_unlock_irqrestore(&ctx->completion_lock, flags);
>  >  
>  > +	/* Ensure read event is completed before putting old page */
>  > +	mutex_lock(&ctx->ring_lock);
>  > +	mutex_unlock(&ctx->ring_lock);
>  >  	put_page(old);
>  >  
>  >  	return rc;
> 
> This looks a bit weird. Would using a completion work here ?

Nope.  This is actually the most elegant fix I've seen for this approach, 
as everything else has relied on adding additional spin locks (which only 
end up being needed in the migration case) around access to the ring_pages 
on the reader side.  That said, this patch is not a complete solution to 
the problem, as the update of the ring's head pointer could still get lost 
with this patch.  I think the right thing is just taking the ring_lock 
mutex over the entire page migration operation.  That should be safe, as 
nowhere else is the ring_lock mutex nested with any other locks.

		-ben

> 	Dave

-- 
"Thought is the essence of where you are now."
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

Powered by blists - more mailing lists