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

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Date:	Wed, 08 Aug 2012 14:40:41 +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 08/07/2012 09:42 PM, Sebastian Andrzej Siewior wrote:
> by the time we get here (after we pass cleanup_ret) uprobe is always is
> set. If it is NULL we leave very early in the code.
>
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
> ---
>   kernel/events/uprobes.c |   16 +++++++---------
>   1 file changed, 7 insertions(+), 9 deletions(-)
>
> diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
> index 41a2555..c8e5204 100644
> --- 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)) ?
> -			/*
> -			 * cannot singlestep; cannot skip instruction;
> -			 * re-execute the instruction.
> -			 */
> -			instruction_pointer_set(regs, bp_vaddr);
> +		/*
> +		 * cannot singlestep; cannot skip instruction;
> +		 * re-execute the instruction.
> +		 */
> +		instruction_pointer_set(regs, bp_vaddr);
>
> -		put_uprobe(uprobe);
> -	}
> +	put_uprobe(uprobe);
>   }

Thanks
Suzuki

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