linux-kernel - Re: [PATCH v5 7/14] x86 support for Uprobes

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Date:	Tue, 15 Jun 2010 13:51:55 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
Cc:	Christoph Hellwig <hch@...radead.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...e.hu>,
	Masami Hiramatsu <mhiramat@...hat.com>,
	Mel Gorman <mel@....ul.ie>,
	Randy Dunlap <rdunlap@...otime.net>,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Roland McGrath <roland@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Mark Wielaard <mjw@...hat.com>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Jim Keniston <jkenisto@...ux.vnet.ibm.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	"Frank Ch. Eigler" <fche@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: Re: [PATCH v5 7/14] x86 support for Uprobes

On 06/15, Srikar Dronamraju wrote:
>
> * Christoph Hellwig <hch@...radead.org> [2010-06-14 13:54:23]:
>
> > On Mon, Jun 14, 2010 at 01:59:13PM +0530, Srikar Dronamraju wrote:
> > > @@ -850,7 +850,19 @@ do_notify_resume(struct pt_regs *regs, void *unused, __u32 thread_info_flags)
> > >
> > >  	if (thread_info_flags & _TIF_UPROBE) {
> > >  		clear_thread_flag(TIF_UPROBE);
> > > +#ifdef CONFIG_X86_32
> > > +		/*
> > > +		 * On x86_32, do_notify_resume() gets called with
> > > +		 * interrupts disabled. Hence enable interrupts if they
> > > +		 * are still disabled.
> > > +		 */
> > > +		native_irq_enable();
> > > +#endif
> > >  		uprobe_notify_resume(regs);
> > > +
> > > +#ifdef CONFIG_X86_32
> > > +		native_irq_disable();
> > > +#endif
> >
> > I'm no x86 port guru, but this looks rather worriesome to me.  Why does
> > do_notify_resume have different calling conventions on 32 vs 64-bit?
> > And if there is a good reason that 32-bit has them disabled, why is
> > enabling them in the middle of do_notify_resume okay?
>
> Thanks for bringing this up. I have no idea about why do_notify_resume()
> gets called with interrupts disabled in 32 bit.

Perhaps just because there is no reason to explicitly enable irqs?

> I would be happy to know
> the reason and rework based on inputs. I did query a few people about
> this but I havent got an answer on why we they are disabled on 32 bit and
> if its Okay to enable at this place.

I think it is OK to enable interrupts. do_notify_resume() calls do_signal()
which enables them anyway.

But there is another question I already asked. Why the code uses
native_irq_enable()? IIRC, you explained that local_irq_enable() doesn't
work for unkown reason. This is strange, and imho should be explained.

And I do not see a need to disable irqs again.

Oleg.

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