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Re: [PATCH -rc] [BUGFIX] x86: fix kernel_trap_sp()
- From: Ingo Molnar <mingo at elte dot hu>
- To: Linus Torvalds <torvalds at linux-foundation dot org>
- Cc: Masami Hiramatsu <mhiramat at redhat dot com>, LKML <linux-kernel at vger dot kernel dot org>, systemtap at sources dot redhat dot com, Harvey Harrison <harvey dot harrison at gmail dot com>, Thomas Gleixner <tglx at linutronix dot de>, Jan Blunck <jblunck at suse dot de>, Christoph Hellwig <hch at infradead dot org>
- Date: Tue, 12 May 2009 00:40:01 +0200
- Subject: Re: [PATCH -rc] [BUGFIX] x86: fix kernel_trap_sp()
- References: <20090511210300.17332.67549.stgit@localhost.localdomain> <alpine.LFD.2.01.0905111512240.3586@localhost.localdomain>
* Linus Torvalds <torvalds@linux-foundation.org> wrote:
> On Mon, 11 May 2009, Masami Hiramatsu wrote:
> >
> > Use ®s->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)(®s->sp);
the original commit had:
> + return (unsigned long)®s->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