linux-kernel - Re: [RFC patch 0/4] TSC calibration improvements

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]

Date:	Sun, 7 Sep 2008 08:01:46 +0200
From:	Willy Tarreau <w@....eu>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Alok Kataria <akataria@...are.com>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	LKML <linux-kernel@...r.kernel.org>,
	Arjan van de Veen <arjan@...radead.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Dan Hecht <dhecht@...are.com>,
	Garrett Smith <garrett@...are.com>
Subject: Re: [RFC patch 0/4] TSC calibration improvements

On Sat, Sep 06, 2008 at 02:10:32PM -0700, Linus Torvalds wrote:

> The fact is, the code that Ingo added was totally bogus. The real bug was 
> that he did a totally bogus "--expect" in the argument to that last call. 

BTW, I hate to see state-changing instructions inside an if condition.
I've been bitten several times while debugging. You try to temporarily
comment out the if statement for a test and you end up with different
code. Same for printf. Examples of dangerous usages :

      i = 0;
      for (x = 0; x < 100; x++) {
         update_var(&i);
         if (debug && i--)
             printf("Hey I'm here\n");
      }
      return i;

You can bet that the if will go away before production. Variant with
similar effects :

      i = 0;
      for (x = 0; x < 100; x++) {
         update_var(&i);
         printf("Hey I'm here : %d\n", --i);
      }
      return i;

Since it costs nothing (except one tab and one LF) to put the instruction
out of the condition, I prefer to see them extracted :

      i = 0;
      for (x = 0; x < 100; x++) {
         update_var(&i);
         i--;
         if (debug)
             printf("Hey I'm here\n");
      }
      return i;
> 

Willy

--
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/