linux-kernel - Re: smp_mb__after_spinlock requirement too strong?

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: <20180312085646.GE4064@hirez.programming.kicks-ass.net>
Date:   Mon, 12 Mar 2018 09:56:46 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Boqun Feng <boqun.feng@...il.com>
Cc:     焦晓冬 <milestonejxd@...il.com>,
        linux-kernel@...r.kernel.org,
        Alan Stern <stern@...land.harvard.edu>, will.deacon@....com,
        torvalds@...ux-foundation.org, npiggin@...il.com, mingo@...nel.org,
        mpe@...erman.id.au, oleg@...hat.com, benh@...nel.crashing.org,
        Paul McKenney <paulmck@...ux.vnet.ibm.com>
Subject: Re: smp_mb__after_spinlock requirement too strong?

On Mon, Mar 12, 2018 at 04:56:00PM +0800, Boqun Feng wrote:
> So I think the purpose of smp_mb__after_spinlock() is to provide RCsc
> locks, it's just the comments before that may be misleading. We want
> RCsc locks in schedule code because we want writes in different critical
> section are ordered even outside the critical sections, for case like:
> 
> 	CPU 0		CPU 1		CPU 2
> 
> 	{A =0 , B = 0}
> 	lock(rq0);
> 	write A=1;
> 	unlock(rq0);
> 
> 			lock(rq0);
> 			read A=1;
> 			write B=2;
> 			unlock(rq0);
> 
> 					read B=2;
> 					smp_rmb();
> 					read A=1;
> 
> I think we need to fix the comments rather than loose the requirement.
> Peter?

Yes, ISTR people relying on schedule() being RCsc, and I just picked a
bad exmaple.