linux-kernel - Re: [PATCH 3/5] uprobes: remove check for uprobe variable in handle

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Date:	Fri, 10 Aug 2012 10:53:09 +0530
From:	"Suzuki K. Poulose" <suzuki@...ibm.com>
To:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
CC:	linux-kernel@...r.kernel.org, x86@...nel.org,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	Roland McGrath <roland@...hat.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Ananth N Mavinakaynahalli <ananth@...ibm.com>,
	stan_shebs@...tor.com
Subject: Re: [PATCH 3/5] uprobes: remove check for uprobe variable in handle_swbp()

On 08/08/2012 03:05 PM, Sebastian Andrzej Siewior wrote:
> On 08/08/2012 11:10 AM, Suzuki K. Poulose wrote:
>>> --- a/kernel/events/uprobes.c
>>> +++ b/kernel/events/uprobes.c
>>> @@ -1528,17 +1528,15 @@ cleanup_ret:
>>> utask->active_uprobe = NULL;
>>> utask->state = UTASK_RUNNING;
>>> }
>>> - if (uprobe) {
>>> - if (!(uprobe->flags & UPROBE_SKIP_SSTEP))
>>> + if (!(uprobe->flags & UPROBE_SKIP_SSTEP))
>>>
>> Shouldn't we check uprobe != NULL before we check the uprobe->flags ?
>> i.e, shouldn't the above line be :
>>
>> if (uprobe && ! (uprobe->flags & UPROBE_SKIP_SSTEP)) ?
>
> The function starts like this:
>
>           if (!uprobe) {
>                   if (is_swbp > 0) {
>                           send_sig(SIGTRAP, current, 0);
>                   } else {
>                           instruction_pointer_set(regs, bp_vaddr);
>                   }
>                   return;
>           }
>
> Which makes uprobe != NULL by the time we get there, no?
>
My bad, was looking at an older version of the function. Also,
the removal of the if (uprobe), check triggered the above question.

Thanks
Suzuki

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