linux-kernel - Re: [PATCH v2 3/3] sched/preempt: fix cond_resched_lock() and cond_resched

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: <20150715133507.GR19282@twins.programming.kicks-ass.net>
Date:	Wed, 15 Jul 2015 15:35:07 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Konstantin Khlebnikov <khlebnikov@...dex-team.ru>
Cc:	Eric Dumazet <eric.dumazet@...il.com>, linux-arch@...r.kernel.org,
	x86@...nel.org, linux-kernel@...r.kernel.org,
	kvm-ppc@...r.kernel.org, Alexander Graf <agraf@...e.de>,
	Paul Mackerras <paulus@...ba.org>,
	David Vrabel <david.vrabel@...rix.com>,
	xen-devel@...ts.xenproject.org,
	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH v2 3/3] sched/preempt: fix cond_resched_lock() and
 cond_resched_softirq()

On Wed, Jul 15, 2015 at 03:52:34PM +0300, Konstantin Khlebnikov wrote:
> On 15.07.2015 15:16, Eric Dumazet wrote:
> >On Wed, 2015-07-15 at 12:52 +0300, Konstantin Khlebnikov wrote:
> >>These functions check should_resched() before unlocking spinlock/bh-enable:
> >>preempt_count always non-zero => should_resched() always returns false.
> >>cond_resched_lock() worked iff spin_needbreak is set.
> >
> >Interesting, this definitely used to work (linux-3.11)
> >
> >Any idea of which commit broke things ?
> >
> 
> Searching... done
> 
> This one: bdb43806589096ac4272fe1307e789846ac08d7c in v3.13
> 
> before
> 
> -static inline int should_resched(void)
> -{
> -       return need_resched() && !(preempt_count() & PREEMPT_ACTIVE);
> -}
> 
> after
> 
> +static __always_inline bool should_resched(void)
> +{
> +       return unlikely(!*preempt_count_ptr());
> +}

Argh, indeed!

> 
> So,
> 
> Fixes: bdb438065890 ("sched: Extract the basic add/sub preempt_count
> modifiers")

Thanks!
--
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/