On Wed, Sep 11, 2013 at 10:56:33AM -0400, Steven Rostedt wrote:
> On Wed, 11 Sep 2013 10:25:45 -0400
> Konrad Rzeszutek Wilk <konrad.w...@oracle.com> wrote:
>
> > > It seems to imply line 53 is the originating bug, so that would be:
> > >
> > > 47 if (type == JUMP_LABEL_ENABLE) {
> > > 48 /*
> > > 49 * We are enabling this jump label. If it is not a nop
> > > 50 * then something must have gone wrong.
> > > 51 */
> > > 52 if (unlikely(memcmp((void *)entry->code, ideal_nop,
> > > 5) != 0))
> > > 53 bug_at((void *)entry->code, __LINE__);
> > >
> > > But it is a NOP isn't it? The code is
> > >
> > > Unexpected op at trace_clock_global+0x6b/0x120 [ffffffff8113a21b] (0f 1f
> > > 44 00 00) 53
> > >
> > > Perhaps the ideal_nop has not been set yet?
> > >
> >
> > And this looks to fix it for me.
>
> I'm trying to understand how this will fix it for you. Are you sure you
> removed 'xen_nopvspin'?
Yes.
>
> If you are calling static_key_slow_inc() before jump_label_init(), then
> it should still fail. The static_key_slow_inc() eventually calls
> arch_jump_label_transform(), which calls __jump_label_transform() with
> init == 0.
Perhaps I am misreading the code, but I believe init is set to one.
That is due to us calling:
arch_jump_label_transform (.., JUMP_LABEL_ENABLE)
which calls __jump_label_transform(.., 1)
?
Perhaps the 'init' and 'enable' parameters have different meanings?
>
> The below code looks to me that it would still compare the contents
> with the ideal_nop, which hasn't been set yet.
In the !init case - sure.
In the init case - just with default_nop.
>
> -- Steve
>
> >
> > diff --git a/arch/x86/kernel/jump_label.c b/arch/x86/kernel/jump_label.c
> > index ee11b7d..d688348 100644
> > --- a/arch/x86/kernel/jump_label.c
> > +++ b/arch/x86/kernel/jump_label.c
> > @@ -44,13 +44,20 @@ static void __jump_label_transform(struct jump_entry
> > *entry,
> > union jump_code_union code;
> > const unsigned char *ideal_nop = ideal_nops[NOP_ATOMIC5];
> >
> > + if (init) {
> > + const unsigned char default_nop[] = { STATIC_KEY_INIT_NOP };
> > + if (unlikely(memcmp((void *)entry->code, default_nop, 5) != 0))
> > + bug_at((void *)entry->code, __LINE__);
> > + }
> > if (type == JUMP_LABEL_ENABLE) {
> > /*
> > * We are enabling this jump label. If it is not a nop
> > * then something must have gone wrong.
> > */
> > - if (unlikely(memcmp((void *)entry->code, ideal_nop, 5) != 0))
> > - bug_at((void *)entry->code, __LINE__);
> > + if (!init) {
> > + if (unlikely(memcmp((void *)entry->code, ideal_nop, 5)
> > != 0))
> > + bug_at((void *)entry->code, __LINE__);
> > + }
> >
> > code.jump = 0xe9;
> > code.offset = entry->target -
> > @@ -62,11 +69,7 @@ static void __jump_label_transform(struct jump_entry
> > *entry,
> > * If this is the first initialization call, then we
> > * are converting the default nop to the ideal nop.
> > */
> > - if (init) {
> > - const unsigned char default_nop[] = {
> > STATIC_KEY_INIT_NOP };
> > - if (unlikely(memcmp((void *)entry->code, default_nop,
> > 5) != 0))
> > - bug_at((void *)entry->code, __LINE__);
> > - } else {
> > + if (!init) {
> > code.jump = 0xe9;
> > code.offset = entry->target -
> > (entry->code + JUMP_LABEL_NOP_SIZE);
>
> --
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