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SubjectRe: [RFC] Recursive printk
At Fri, 5 Dec 2008 23:41:05 -0800,
Andrew Morton wrote:
>
> On Sat, 6 Dec 2008 08:33:05 +0100 Willy Tarreau <w@1wt.eu> wrote:
>
> > 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
>
> Good heavens, so it does. It is unusual for C to cater to such stupid
> code by generating such inefficient code. A bit of a trap, really.

Indeed the tmp string isn't needed to be there.
Simply
printk("<%c>ALSA %s:%d: ", format[1], file, line);
should suffice. Though, the efficiency doesn't matter so much in this
case...


Takashi


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