linux-kernel - Re: [PATCH 21/24] blkcg: make blkcg_print_blkgs() grab q locks instead of blkcg lock

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 linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Wed, 2 Jan 2013 15:45:27 -0500
From:	Tejun Heo <tj@...nel.org>
To:	Vivek Goyal <vgoyal@...hat.com>
Cc:	lizefan@...wei.com, axboe@...nel.dk,
	containers@...ts.linux-foundation.org, cgroups@...r.kernel.org,
	linux-kernel@...r.kernel.org, ctalbott@...gle.com, rni@...gle.com
Subject: Re: [PATCH 21/24] blkcg: make blkcg_print_blkgs() grab q locks
 instead of blkcg lock

On Wed, Jan 02, 2013 at 02:27:00PM -0500, Vivek Goyal wrote:
> On Fri, Dec 28, 2012 at 12:35:43PM -0800, Tejun Heo wrote:
> > Instead of holding blkcg->lock while walking ->blkg_list and executing
> > prfill(), RCU walk ->blkg_list and hold the blkg's queue lock while
> > executing prfill().  This makes prfill() implementations easier as
> > stats are mostly protected by queue lock.
> > 
> > This will be used to implement hierarchical stats.
> > 
> 
> Hi Tejun,
> 
> I think dropping blkcg->lock might be a problem. Using RCU we have made
> sure that blkg and q are around. But what about blkg->q.backing_dev_info.dev.
> 
> We can follow bdi->dev pointer in blkg_dev_name(). I am not sure if we
> ever clear it from q or not when device goes away.

If the queue is dead, it wouldn't have policy enabled bit set which is
tested while holding queue lock, so I don't think it's gonna be a
problem.

Thanks.

-- 
tejun
--
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/