linux-kernel - Re: [PATCH 1/2] brw_mutex: big read-write mutex

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Message-ID: <20121026120605.GA23545@redhat.com>
Date:	Fri, 26 Oct 2012 14:06:05 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Dave Chinner <david@...morbit.com>
Cc:	Mikulas Patocka <mpatocka@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Anton Arapov <anton@...hat.com>, linux-kernel@...r.kernel.org,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 1/2] brw_mutex: big read-write mutex

On 10/26, Dave Chinner wrote:
>
> On Thu, Oct 25, 2012 at 10:09:31AM -0400, Mikulas Patocka wrote:
> >
> > Yes, mnt_want_write()/mnt_make_readonly() do the same thing as percpu rw
> > semaphores. I think you can convert mnt_want_write()/mnt_make_readonly()
> > to use percpu rw semaphores and remove the duplicated code.
>
> I think you misunderstood my point - that rather than re-inventing
> the wheel, why didn't you just copy something that is known to
> work?

I don't understand why do you both think that __mnt_want_write()
and mnt_make_readonly() provides the same functionality. I looked
at this code before I started this patch, and unless I completely
misread it this does very different things. It is not "lock" at all.

Oleg.

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