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

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Date:	Tue, 15 Jun 2010 11:53:32 +0530
From:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	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>,
	Oleg Nesterov <oleg@...hat.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

* 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. 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. 

Ingo, Is there any person whom I could check with to get to know why the
interrupts are disabled on x86_32?

> 
> > +void arch_uprobe_disable_sstep(struct pt_regs *regs)
> > +{
> > +		/* Disable single-stepping by clearing what we set */
> > +		clear_thread_flag(TIF_SINGLESTEP);
> > +		clear_thread_flag(TIF_FORCED_TF);
> > +		regs->flags &= ~X86_EFLAGS_TF;
> > +}
> 
> This seems to have one layer of indentation too much.

Okay, I shall fix this in the next iteration.

--
Thanks and Regards
Srikar


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