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

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Date:	Tue, 15 Jun 2010 15:15:12 +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:
>
> > 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);

I see, and my question is why PVOP_VCALLEE0(pv_irq_ops.irq_enable) doesn't
work ? If it doesn't here, why it works for other callers of local_irq_enable?

I think we should ask paravirt developers.

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

I dunno, and I know nothing about paravirt.

But please note that currently native_irq_enable has the only caller,
raw_local_irq_enable(). It is really strange that do_notify_resume()
has to use it, and it uses it to bypass the paravirt layer which perhaps
can introduce other problems.

Oleg.

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