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

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Date:	Wed, 08 Aug 2012 11:35:26 +0200
From:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:	"Suzuki K. Poulose" <suzuki@...ibm.com>
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 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?

Sebastian
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