From: "Rafael J. Wysocki" <rjw@sisk.pl>
To: Pavel Machek <pavel@ucw.cz>
Subject: Re: [PATCH 2.6.19 5/5] fs: freeze_bdev with semaphore not mutex
Date: Thu, 9 Nov 2006 23:21:46 +0100
User-Agent: KMail/1.9.1
Cc: Alasdair G Kergon <agk@redhat.com>, Eric Sandeen <sandeen@redhat.com>,
       Andrew Morton <akpm@osdl.org>, linux-kernel@vger.kernel.org,
       dm-devel@redhat.com, Srinivasa DS <srinivasa@in.ibm.com>,
       Nigel Cunningham <nigel@suspend2.net>, David Chinner <dgc@sgi.com>
References: <20061107183459.GG6993@agk.surrey.redhat.com> <200611092218.58970.rjw@sisk.pl> <20061109214159.GB2616@elf.ucw.cz>
In-Reply-To: <20061109214159.GB2616@elf.ucw.cz>
MIME-Version: 1.0
Content-Type: text/plain;
  charset="iso-8859-1"
Content-Transfer-Encoding: 7bit
Content-Disposition: inline
Message-Id: <200611092321.47728.rjw@sisk.pl>
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1878
Lines: 49

On Thursday, 9 November 2006 22:41, Pavel Machek wrote:
> Hi!
> 
> > > > This is from a work queue, so in fact from a process context, but from
> > > > a process that is running with PF_NOFREEZE.
> > > 
> > > Why not simply &~ PF_NOFREEZE on that particular process? Filesystems
> > > are free to use threads/work queues/whatever, but refrigerator should
> > > mean "no writes to filesystem" for them...
> > 
> > But how we differentiate worker_threads used by filesystems from the
> > other ones?
> 
> I'd expect filesystems to do &~ PF_NOFREEZE by hand.
> 
> > BTW, I think that worker_threads run with PF_NOFREEZE for a reason,
> > but what exactly is it?
> 
> I do not think we had particulary good reasons...

Well, it looks like quite a lot of drivers depend on them, including libata.

I think we can add a flag to __create_workqueue() that will indicate if
this one is to be running with PF_NOFREEZE and a corresponding macro like
create_freezable_workqueue() to be used wherever we want the worker thread
to freeze (in which case it should be calling try_to_freeze() somewhere).
Then, we can teach filesystems to use this macro instead of
create_workqueue().

Having done that we'd be able to drop the freezing of bdevs patch and forget
about the dm-related complexity.

[Still I wonder if the sys_sync() in freeze_processes() is actually safe if
there's a suspended dm device somewhere in the stack, because in the other
case the freezing of bdevs would be no more dangerous than the thing
that we're already doing.]

Greetings,
Rafael


-- 
You never change things by fighting the existing reality.
		R. Buckminster Fuller
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/