linux-kernel - Re: [PATCH 2/2] irq_work: Fix racy IRQ_WORK

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: <CAFTL4hx7Xu9hy1ASQgsadvi4bq3L_DgyLWkpY0ZA-Tpmf01y4Q@mail.gmail.com>
Date:	Wed, 31 Oct 2012 14:32:33 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	anish kumar <anish198519851985@...il.com>,
	Paul McKenney <paulmck@...ux.vnet.ibm.com>,
	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 2/2] irq_work: Fix racy IRQ_WORK_BUSY flag setting

2012/10/31 Steven Rostedt <rostedt@...dmis.org>:
> On Wed, 2012-10-31 at 20:04 +0900, anish kumar wrote:
>> nflags = 1 | 3
>> nflags = 2 | 3
>> In both cases the result would be same.If I am right then wouldn't this
>> operation be redundant?
>
> Right. Actually we could change the new loop to:
>
>         for (;;) {
>                 oflags = cmpxchg(&work->flags, flags, IRQ_WORK_FLAGS);
>                 if (oflags == flags)
>                         break;
>                 if (oflags & IRQ_WORK_PENDING)
>                         return false;
>                 flags = oflags;
>                 cpu_relax();
>         }

We could. But I wanted to keep the code able to handle new flags in
the future (such as IRQ_WORK_LAZY).

> Frederic,
>
> Would you like to add my explanation to your change log? You can add the
> entire thing, which I think would explain a lot to people.

It's indeed a very clear explanation. I'll put that in the changelog, 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/