Re: [CHECKER] large stack variables (>=1K) in 2.4.4 and 2.4.4-ac8

[Andrew Morton <andrewm@uow.edu.au>]

Andreas Dilger wrote:
> 
> Dawson Engler writes:
> > Here are 37 errors where variables >= 1024 bytes are allocated on a
> > function's stack.
> 
> First of all, thanks very much for the work you are doing.  It really
> is useful, and a good way to catch those very rare error cases that
> would not otherwise be fixed.
> 
> I'm curious about this stack checker.  Does it check for a single
> stack allocation >= 1024 bytes, or does it also check for several
> individual, smaller allocations which total >= 1024 bytes inside
> a single function?  That would be equally useful.
> 
> On a side note, does anyone know if the kernel does checking if the
> stack overflowed at any time?

There's a little bit of code in show_task() which calculates
how close this task ever got to overrunning its kernel stack:

        {
                unsigned long * n = (unsigned long *) (p+1);
                while (!*n)
                        n++;
                free = (unsigned long) n - (unsigned long)(p+1);
        }
        printk("%5lu %5d %6d ", free, p->pid, p->p_pptr->pid);

SYSRQ-T will trigger this.

However it doesn't work, because do_fork() doesn't zero
out the stack pages when they're created.

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