Re: [PATCH] x86 entry_64.S lockdep fix

[Ingo Molnar]

* Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxx> wrote:

> * Steven Rostedt (rostedt@xxxxxxxxxxx) wrote:
> > 
> > On Fri, 17 Apr 2009, Mathieu Desnoyers wrote:
> > > 
> > > I happened to have the following patch hanging around in my LTTng tree
> > > for a while. Would it solve your problem by any chance ? I had to move
> > > it a bit around in my patchset to put it before the nmi-safe int3
> > > handler patch I have, but it should apply correctly.
> > > 
> > > 
> > > x86 entry_64.S lockdep fix
> > > 
> > > Add missing lockdep irq on instrumentation to entry_64.S.
> > > 
> > > Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxx>
> > > ---
> > >  arch/x86/kernel/entry_64.S |    2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > > 
> > > Index: linux-2.6-lttng/arch/x86/kernel/entry_64.S
> > > ===================================================================
> > > --- linux-2.6-lttng.orig/arch/x86/kernel/entry_64.S	2009-04-17 17:44:18.000000000 -0400
> > > +++ linux-2.6-lttng/arch/x86/kernel/entry_64.S	2009-04-17 17:53:42.000000000 -0400
> > > @@ -1420,9 +1420,9 @@ ENTRY(paranoid_exit)
> > >  	testl $3,CS(%rsp)
> > >  	jnz   paranoid_userspace
> > >  paranoid_swapgs:
> > > -	TRACE_IRQS_IRETQ 0
> > >  	SWAPGS_UNSAFE_STACK
> > >  paranoid_restore:
> > > +	TRACE_IRQS_IRETQ 0
> > 
> > This is buggy. If you go here via userspace, you just did a swapgs, and 
> > the %gs register (process context) is now zero. If you call kernel code 
> > that does anything with "current" you will crash the system.
> > 
> 
> Argh, I should not have extracted my fix from my patchset and try to
> reorder the patches that late in the day. Sorry, you are indeed right.
> On the bright side, the patch I send earlier has never hit a repository.
> Here is a more sensible version.
> 
> 
> Add missing lockdep irq on instrumentation to entry_64.S.
> 
> Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxx>
> ---
>  arch/x86/kernel/entry_64.S |    3 +++
>  1 file changed, 3 insertions(+)
> 
> Index: linux-2.6-lttng/arch/x86/kernel/entry_64.S
> ===================================================================
> --- linux-2.6-lttng.orig/arch/x86/kernel/entry_64.S	2009-04-17 18:34:51.000000000 -0400
> +++ linux-2.6-lttng/arch/x86/kernel/entry_64.S	2009-04-18 23:41:28.000000000 -0400
> @@ -1422,7 +1422,10 @@ ENTRY(paranoid_exit)
>  paranoid_swapgs:
>  	TRACE_IRQS_IRETQ 0
>  	SWAPGS_UNSAFE_STACK
> +	RESTORE_ALL 8
> +	jmp irq_return
>  paranoid_restore:
> +	TRACE_IRQS_IRETQ 0
>  	RESTORE_ALL 8
>  	jmp irq_return
>  paranoid_userspace:

Yeah - that is exactly the fix from Steve that i have queued up two 
days ago - see it attached below.

	Ingo

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