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

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]

Message-ID: <Pine.LNX.4.64.1210261208010.5413@file.rdu.redhat.com>
Date:	Fri, 26 Oct 2012 12:09:41 -0400 (EDT)
From:	Mikulas Patocka <mpatocka@...hat.com>
To:	Oleg Nesterov <oleg@...hat.com>
cc:	Dave Chinner <david@...morbit.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 Fri, 26 Oct 2012, Oleg Nesterov wrote:

> > The code is different, but it can be changed to use percpu rw semaphores
> > (if we add percpu_down_write_trylock).
> 
> I don't really understand how you can make percpu_down_write_trylock()
> atomic so that it can be called under br_write_lock(vfsmount_lock) in
> sb_prepare_remount_readonly(). So I guess you also need to replace
> vfsmount_lock at least. Or _trylock needs the barriers in _down_read.
> Or I missed something.
> 
> Oleg.

That's true - that code is under spinlock and you can't implement 
non-blocking percpu_down_write_trylock.

Mikulas
--
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/