Re: [RFC] Recursive printk

[Willy Tarreau <w@1wt.eu>]

On Fri, Dec 05, 2008 at 11:20:16PM -0800, Andrew Morton wrote:
> > void snd_verbose_printk(const char *file, int line, const char *format, ...)
> > {
> >         va_list args;
> > 
> >         if (format[0] == '<' && format[1] >= '0' && format[1] <= '7' && format[2] == '>') {
> >                 char tmp[] = "<0>";
> >                 tmp[1] = format[1];
> >                 printk("%sALSA %s:%d: ", tmp, file, line);
> >                 format += 3;
> 
> That's racy.  Two threads can fight over tmp[1].  It should do:
> 
> 		printk("<%c>ALSA %s:%d: ", format[1], tmp, file, line);
> 
> (I didn't know that you can even modify literal strings - shouldn't
> they be in read-only storage?)

no Andrew, this tmp[] is declared on the stack, and gcc emits code to
copy the constant "<0>" onto the stack every time this code is called
(which is basically just a 32-bit integer copy). So there's no race
either.

Regards,
Willy