linux-kernel - Re: [PATCH] x86/aperfmperf: use time_is_before_jiffies(a + b) to replace "jiffies

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] [day] [month] [year] [list]

Message-ID: <YuJlLK4x9aUuqHQZ@worktop.programming.kicks-ass.net>
Date:   Thu, 28 Jul 2022 12:30:04 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Yu Zhe <yuzhe@...china.com>
Cc:     tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
        dave.hansen@...ux.intel.com, x86@...nel.org, hpa@...or.com,
        linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org,
        liqiong@...china.com
Subject: Re: [PATCH] x86/aperfmperf: use time_is_before_jiffies(a + b) to
 replace "jiffies - a > b"

On Thu, Jul 28, 2022 at 10:55:51AM +0800, Yu Zhe wrote:
> 在 2022年07月28日 00:00, Peter Zijlstra 写道:
> 
> > On Wed, Jul 27, 2022 at 11:14:05AM +0800, Yu Zhe wrote:
> > > time_is_before_jiffies deals with timer wrapping correctly.
> > Please explain how the current code does not.
> 
> 1. If the timer wrap changes in the future you won't have to alter your code.
> 
> 2. unsigned long ut;
> 
>    ut = ULONG_MAX + 4;
> 
>    printf("time_after(ut, ULONG_MAX), ut:%d, %d --> %d\n", ut,
>              time_after(ut, ULONG_MAX), (ULONG_MAX - ut) < 0);
> 
> 
>    In this case, time_after returns true, it's correct.

Now try the same with the existing code...