linux-kernel - Re: [PATCH 0/2] irq

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: <CAFTL4hzhTtx_OFeRE+RzsPvMWXr0ncbAjkFhEV-TE_XAFVNbdg@mail.gmail.com>
Date:	Tue, 30 Oct 2012 17:25:41 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Paul Gortmaker <paul.gortmaker@...driver.com>
Subject: Re: [PATCH 0/2] irq_work: A couple fixes

2012/10/30 Steven Rostedt <rostedt@...dmis.org>:
> On Tue, 2012-10-30 at 16:34 +0100, Frederic Weisbecker wrote:
>> Hi,
>
>> And I still wonder if cpu_relax() is enough to prevent the compiler
>> from correctly reloading work->flags in irq_work_sync() loop.
>> Do we need ACCESS_ONCE()?
>
> You mean this loop:
>
>        flags = work->flags & ~IRQ_WORK_PENDING;
>        for (;;) {
>                nflags = flags | IRQ_WORK_FLAGS;
>                oflags = cmpxchg(&work->flags, flags, nflags);
>                if (oflags == flags)
>                        break;
>                if (oflags & IRQ_WORK_PENDING)
>                        return false;
>                flags = oflags;
>                cpu_relax();
>        }
>
> After the first loading of work->flags, you are worried about the
> &work->flags in the cmpxchg()?  The cmpxchg() will handle that itself. I
> don't see any place that a ACCESS_ONCE() is required here. The cmpxchg()
> acts on the address of work->flags, the compiler isn't involved with the
> value at that address.

No I was worried about the cpu_relax() in irq_work_sync()
--
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/