linux-kernel - Re: [PATCH RFC v4 1/6] arm64: support single-step and breakpoint handler hooks

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Message-ID: <20131203194412.GC22668@mudshark.cambridge.arm.com>
Date:	Tue, 3 Dec 2013 19:44:12 +0000
From:	Will Deacon <will.deacon@....com>
To:	Sandeepa Prabhu <sandeepa.prabhu@...aro.org>
Cc:	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"patches@...aro.org" <patches@...aro.org>,
	"linaro-kernel@...ts.linaro.org" <linaro-kernel@...ts.linaro.org>,
	Catalin Marinas <Catalin.Marinas@....com>,
	"steve.capper@...aro.org" <steve.capper@...aro.org>,
	"nico@...aro.org" <nico@...aro.org>,
	"srikar@...ux.vnet.ibm.com" <srikar@...ux.vnet.ibm.com>,
	"rostedt@...dmis.org" <rostedt@...dmis.org>,
	"masami.hiramatsu.pt@...achi.com" <masami.hiramatsu.pt@...achi.com>,
	"dsaxena@...aro.org" <dsaxena@...aro.org>,
	"jiang.liu@...wei.com" <jiang.liu@...wei.com>,
	"Vijaya.Kumar@...iumnetworks.com" <Vijaya.Kumar@...iumnetworks.com>
Subject: Re: [PATCH RFC v4 1/6] arm64: support single-step and breakpoint
 handler hooks

On Tue, Dec 03, 2013 at 02:33:17PM +0000, Sandeepa Prabhu wrote:
> Hi Will,
> 
> Sorry for responding to this after long-time, I missed this review
> during Linaro connect travels.

No problem.

> >> @@ -215,7 +257,10 @@ static int single_step_handler(unsigned long addr, unsigned int esr,
> >>                */
> >>               user_rewind_single_step(current);
> >>       } else {
> >> -             /* TODO: route to KGDB */
> >> +             /* call registered single step handlers */
> >
> > Don't bother with this comment (it's crystal clear from the code).
> OK, I will remove this unnecessary print.

Thanks.

> >> +static LIST_HEAD(break_hook);
> >> +DEFINE_RWLOCK(break_hook_lock);
> >
> > This guy can be a plain old spinlock. That way, the readers have less
> > overhead but things still work because we only call a single hook function.
> well, kprobes need to support recursive breakpoints (i.e. breakpoint
> handler executing BRK once again)
> so I converted this lock to rw_lock.  I should put this info in commit
> description to be more clearer.

Actually, this is one place where a comment in the code *would* be useful!

> Let me know if you find any issue with re-cursing in breakpoint exception?

Sounds ok to me. With those changes:

  Acked-by: Will Deacon <will.deacon@....com>

Cheers,

Will
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