linux-kernel - Re: Question about C language.

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]

Date:	Sun, 23 Mar 2008 03:30:10 -0400
From:	Chris Snook <csnook@...hat.com>
To:	Francis Moreau <francis.moro@...il.com>
CC:	linux-kernel@...r.kernel.org
Subject: Re: Question about C language.

Francis Moreau wrote:
> Hello,
> 
> I know it's a bit out of topic but this is something I need to clarify for
> writing a Linux driver... hope you don't mind.
> 
> In my driver I have a global variable that controls a loop such as:
> 
> int my_condition;
> 
> void change_my_condition(int new)
> {
>     my_condition = new;
> }
> 
> int foo(void)
> {
>     /* irqs are disabled */
>     my_condition = 1;
>     do {
>         ....
>         local_irq_enable();
>         cpu_sleep();
>         local_irq_disable();
> 
>    } while (my_condition);
> 
> }
> 
> This variable is modified by an interrupt handler define in another file
> by using 'change_my_condition' function.
> 
> By reading the ISO C99 specification, I _think_ that I needn't any
> kind of barrier
> or even use the volatile type qualifier for my_condition variable to make a true
> access to 'my_condition' in the controlling expression of the while, but I'm not
> sure.
> 
> Coud anybody confirm ?
> 
> Thanks,

Even volatile may be insufficient with some architecture/compiler 
combinations.  You should use explicit barriers wherever you need them, 
or Bad Things will happen.

-- Chris
--
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/