linux-kernel - Re: [PATCH 1/4] spinlock: Document memory barrier rules

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: <20160829104815.GI10153@twins.programming.kicks-ass.net>
Date:   Mon, 29 Aug 2016 12:48:15 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Manfred Spraul <manfred@...orfullife.com>
Cc:     benh@...nel.crashing.org, paulmck@...ux.vnet.ibm.com,
        Ingo Molnar <mingo@...e.hu>, Boqun Feng <boqun.feng@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>, 1vier1@....de,
        Davidlohr Bueso <dave@...olabs.net>
Subject: Re: [PATCH 1/4] spinlock: Document memory barrier rules

On Sun, Aug 28, 2016 at 01:56:13PM +0200, Manfred Spraul wrote:
> Right now, the spinlock machinery tries to guarantee barriers even for
> unorthodox locking cases, which ends up as a constant stream of updates
> as the architectures try to support new unorthodox ideas.
> 
> The patch proposes to reverse that:
> spin_lock is ACQUIRE, spin_unlock is RELEASE.
> spin_unlock_wait is also ACQUIRE.
> Code that needs further guarantees must use appropriate explicit barriers.
> 
> Architectures that can implement some barriers for free can define the
> barriers as NOPs.
> 
> As the initial step, the patch converts ipc/sem.c to the new defines:
> - no more smp_rmb() after spin_unlock_wait(), that is part of
>   spin_unlock_wait()
> - smp_mb__after_spin_lock() instead of a direct smp_mb().
> 

Why? This does not explain why..