linux-kernel - Re: [PATCH 1/4] oprofile: Handle initialisation failure more gracefully

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Message-ID: <20100827124344.GJ22783@erda.amd.com>
Date:	Fri, 27 Aug 2010 14:43:44 +0200
From:	Robert Richter <robert.richter@....com>
To:	Matt Fleming <matt@...sole-pimps.org>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Will Deacon <will.deacon@....com>,
	Paul Mundt <lethal@...ux-sh.org>,
	Russell King <linux@....linux.org.uk>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-sh@...r.kernel.org" <linux-sh@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...e.hu>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	"linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>
Subject: Re: [PATCH 1/4] oprofile: Handle initialisation failure more
 gracefully

On 26.08.10 15:09:16, Matt Fleming wrote:
> From: Will Deacon <will.deacon@....com>
> 
> The current implementation is not entirely safe in the case that
> oprofile_arch_init() fails. We need to make sure that we always call
> exit_driverfs() if we've called init_driverfs(). Also, avoid a potential
> double free when freeing 'counter_config', e.g. don't free
> 'counter_config' in both oprofile_arch_init() and oprofile_arch_exit().
> 
> Signed-off-by: Will Deacon <will.deacon@....com>
> ---
>  arch/arm/oprofile/common.c |   15 ++++++++-------
>  1 files changed, 8 insertions(+), 7 deletions(-)
> 
> diff --git a/arch/arm/oprofile/common.c b/arch/arm/oprofile/common.c
> index 0691176..482779c 100644
> --- a/arch/arm/oprofile/common.c
> +++ b/arch/arm/oprofile/common.c
> @@ -275,10 +275,12 @@ out:
>  	return ret;
>  }
>  
> -static void  exit_driverfs(void)
> +static void exit_driverfs(void)
>  {
> -	platform_device_unregister(oprofile_pdev);
> -	platform_driver_unregister(&oprofile_driver);
> +	if (!IS_ERR_OR_NULL(oprofile_pdev)) {
> +		platform_device_unregister(oprofile_pdev);
> +		platform_driver_unregister(&oprofile_driver);
> +	}

The root cause that makes this check necessary is that
oprofile_arch_exit() is called though oprofile_arch_init() failed. We
should better fix this instead. I have to admit we will then have to
check all architectural implementations.

>  }
>  #else
>  static int __init init_driverfs(void) { return 0; }
> @@ -363,10 +365,8 @@ int __init oprofile_arch_init(struct oprofile_operations *ops)
>  	}
>  
>  	ret = init_driverfs();
> -	if (ret) {
> -		kfree(counter_config);

We should not return from oprofile_arch_init() with allocated
resources if the function fails. To fix duplicate kfrees, we should
free it here and then set counter_config to NULL. It should also be
freed if for_each_possible_cpu() or op_name_from_perf_id() fails.

Also, the pointer should be NULLed after freeing in
oprofile_arch_exit(). There, we also don't need the NULL pointer check
as it is save to call kfree(NULL).

-Robert

> +	if (ret)
>  		return ret;
> -	}
>  
>  	for_each_possible_cpu(cpu) {
>  		perf_events[cpu] = kcalloc(perf_num_counters,
> @@ -401,8 +401,9 @@ void oprofile_arch_exit(void)
>  	int cpu, id;
>  	struct perf_event *event;
>  
> +	exit_driverfs();
> +
>  	if (*perf_events) {
> -		exit_driverfs();
>  		for_each_possible_cpu(cpu) {
>  			for (id = 0; id < perf_num_counters; ++id) {
>  				event = perf_events[cpu][id];
> -- 
> 1.7.1
> 
> 

-- 
Advanced Micro Devices, Inc.
Operating System Research Center

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