Re: x86_64: could increment fp when getting wchan?
From: Thomas Gleixner
Date: Fri Jan 21 2011 - 09:05:37 EST
On Fri, 21 Jan 2011, Hillf Danton wrote:
> When getting wchan (wait channel?) the stack of given task is scanned
> for IP that is not in the scheduling area. What looks odd is the IP
> could be checked as many times as allowed in the loop without changing
> the location on stack. Could the IP be checked up stair the stack?
Errm.
> Hillf
> ---
>
> --- a/arch/x86/kernel/process_64.c 2011-01-05 08:50:20.000000000 +0800
> +++ b/arch/x86/kernel/process_64.c 2011-01-21 21:46:04.000000000 +0800
> @@ -543,7 +543,7 @@ unsigned long get_wchan(struct task_stru
> ip = *(u64 *)(fp+8);
IP (Return address) is read from stack via fp (Frame pointer)
> if (!in_sched_functions(ip))
> return ip;
> - fp = *(u64 *)fp;
Now fp is set to the next stack frame, so the next loop will read a
different IP.
> + fp += 8;
> } while (count++ < 16);
> return 0;
> }
Thanks,
tglx
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/