linux-kernel - Re: [patch] queued spinlocks (i386)

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: Windows password security audit tool. GUI, reports in PDF.

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

Message-ID: <Pine.LNX.4.64.0703291215440.1199@alien.or.mcafeemobile.com>
Date:	Thu, 29 Mar 2007 15:16:49 -0700 (PDT)
From:	Davide Libenzi <davidel@...ilserver.org>
To:	Oleg Nesterov <oleg@...sign.ru>
cc:	Nick Piggin <npiggin@...e.de>,
	Ravikiran G Thirumalai <kiran@...lex86.org>,
	Ingo Molnar <mingo@...e.hu>,
	Nikita Danilov <nikita@...sterfs.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [patch] queued spinlocks (i386)

On Thu, 29 Mar 2007, Oleg Nesterov wrote:

> On 03/28, Nick Piggin wrote:
> >
> > Well with my queued spinlocks, all that lockbreak stuff can just come out
> > of the spin_lock, break_lock out of the spinlock structure, and
> > need_lockbreak just becomes (lock->qhead - lock->qtail > 1).
> 
> Q: queued spinlocks are not CONFIG_PREEMPT friendly,

Why? Is CONFIG_PREEMPT friendly to anyone? :)



> > +       asm volatile(LOCK_PREFIX "xaddw %0, %1\n\t"
> > +                    : "+r" (pos), "+m" (lock->qhead) : : "memory");
> > +       while (unlikely(pos != lock->qtail))
> > +               cpu_relax();
> 
> once we incremented lock->qhead, we have no optiion but should spin with
> preemption disabled until pos == lock->qtail, yes?

Yes, preemption and deterministic spinlock policies are not friends.



- Davide


-
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/