Date: Tue, 15 Jun 2010 11:53:32 +0530
From: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
To: Christoph Hellwig <hch@infradead.org>
Cc: Peter Zijlstra <peterz@infradead.org>, Ingo Molnar <mingo@elte.hu>,
       Masami Hiramatsu <mhiramat@redhat.com>, Mel Gorman <mel@csn.ul.ie>,
       Randy Dunlap <rdunlap@xenotime.net>,
       Arnaldo Carvalho de Melo <acme@infradead.org>,
       Steven Rostedt <rostedt@goodmis.org>,
       Roland McGrath <roland@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
       Ananth N Mavinakayanahalli <ananth@in.ibm.com>,
       Oleg Nesterov <oleg@redhat.com>, Mark Wielaard <mjw@redhat.com>,
       Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
       Andrew Morton <akpm@linux-foundation.org>,
       Linus Torvalds <torvalds@linux-foundation.org>,
       Frederic Weisbecker <fweisbec@gmail.com>,
       Jim Keniston <jkenisto@linux.vnet.ibm.com>,
       "Rafael J. Wysocki" <rjw@sisk.pl>, "Frank Ch. Eigler" <fche@redhat.com>,
       LKML <linux-kernel@vger.kernel.org>,
       "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Subject: Re: [PATCH v5 7/14] x86 support for Uprobes
Message-ID: <20100615062332.GE13800@linux.vnet.ibm.com>
Reply-To: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
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 <20100614175423.GG23754@infradead.org>
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* Christoph Hellwig <hch@infradead.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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