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

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Message-ID: <20100615121506.GM13800@linux.vnet.ibm.com>
Date:	Tue, 15 Jun 2010 17:45:06 +0530
From:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
To:	Oleg Nesterov <oleg@...hat.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

> > >
> > > 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.
> 

local_irq_enable() translates to raw_local_irq_enable().
However raw_local_irq_enable on x86 seems to depend on CONFIG_PARAVIRT.
On a machine, where CONFIG_PARAVIRT was defined, local_irq_enable
translates to something other than native_irq_enable.
It translates to PVOP_VCALLEE0(pv_irq_ops.irq_enable);

Is it okay to use local_irq_enable() and then make CONFIG_UPROBES depend
on !CONFIG_PARAVIRT?



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