Re: [PATCH -rc] [BUGFIX] x86: fix kernel_trap_sp()

From: Ingo Molnar
Date: Mon May 11 2009 - 18:40:55 EST



* Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:

> On Mon, 11 May 2009, Masami Hiramatsu wrote:
> >
> > Use &regs->sp instead of regs for getting the top of stack in kernel mode.
> > (on x86-64, regs->sp always points the top of stack)
>
> Ack.
>
> That said, we have only _one_ use of this "kernel_trap_sp()" in
> the whole kernel, and that use is actually fairly odd too, in that
> it does it _before_ checking that it's in kernel mode.
>
> Admittedly it will then only _use_ the value after it has checked
> that things are in kernel mode, but it all boils down to "ok,
> that's pretty odd".
>
> So how about fixing that, and also fixing the naming of the
> function. Call it "kernel_stack_pointer()" to match its more
> widely used sibling function "user_stack_pointer()".
>
> IOW, something like this?

yeah, this is cleaner and probably a tad faster. I've applied it to
x86/urgent with your acked-by - or would you like to apply this
straight away?

The use of the backtracing feature on the oprofile side is not very
common (and the bug is ancient) so i wanted to wait a few days with
this.

One small detail:

> + return (unsigned long)(&regs->sp);

the original commit had:

> + return (unsigned long)&regs->sp;

and this latter is correct as well due to operator priorities. No
strong preference from my side so i took your version as-is. I kept
Masami as the author and a comment for your changes.

( Not sure how to express this in a changelog properly - i didnt
want two commits but it was authored by two people in essence. So
i went for the version that will show up in the commit
notification email in a few minutes - also attached below. )

Ingo
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