linux-kernel - Re: [PATCH v2] locktorture: Fix NULL pointer when torture

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Date:	Mon, 7 Mar 2016 10:00:52 +0800
From:	Kefeng Wang <wangkefeng.wang@...wei.com>
To:	Davidlohr Bueso <dave@...olabs.net>
CC:	<paulmck@...ux.vnet.ibm.com>, <linux-kernel@...r.kernel.org>,
	<peterz@...radead.org>, <mingo@...hat.com>,
	Josh Triplett <josh@...htriplett.org>,
	"Guohanjun (Hanjun Guo)" <guohanjun@...wei.com>
Subject: Re: [PATCH v2] locktorture: Fix NULL pointer when torture_type is
 invalid



On 2016/3/3 16:36, Davidlohr Bueso wrote:
> On Thu, 03 Mar 2016, Kefeng Wang wrote:
> 

> 
> The below should take care of both issues, what do you think?
> 
> Thanks,
> Davidlohr
> 
> <8-------------------------------------------------------------------------
> Subject: [PATCH] locktorture: Fix nil pointer dereferencing for cleanup paths
> 
> It has been found that paths that invoke cleanups through
> lock_torture_cleanup() can incur in nil pointer dereferencing
> bugs during the statistics printing phase. This is mainly
> because we should not be calling into statistics before we are
> sure things have been setup correctly.
> 
> Specifically, early checks (and the need for handling this in
> the cleanup call) only include parameter checks and basic
> statistics allocation. Once we start write/read kthreads
> we then consider the test as started. As such, update the func
> in question to check for cxt.lwsa writer stats, if not set,
> we either have a bogus parameter or ENOMEM situation and
> therefore only need to deal with general torture calls.
> 
> Signed-off-by: Davidlohr Bueso <dbueso@...e.de>
> ---
> XXX: while looking at the code, do we need at least a stat_interval > 0
> check before stopping the lock_torture_stats kthread?
> 
>  kernel/locking/locktorture.c | 11 +++++++++++
>  1 file changed, 11 insertions(+)
> 
> diff --git a/kernel/locking/locktorture.c b/kernel/locking/locktorture.c
> index 8ef1919..1942848 100644
> --- a/kernel/locking/locktorture.c
> +++ b/kernel/locking/locktorture.c
> @@ -748,6 +748,15 @@ static void lock_torture_cleanup(void)
>      if (torture_cleanup_begin())
>          return;
>  
> +    /*
> +     * Indicates early cleanup, meaning that the test has not run,
> +     * such as when passing bogus args when loading the module. As
> +     * such, only perform the underlying torture-specific cleanups,
> +     * and avoid anything related to locktorture.
> +     */
> +    if (!cxt.lwsa)
> +        goto end;

Sorry for the late response, the cxt.lrsa should be taken into account too.

> +
>      if (writer_tasks) {
>          for (i = 0; i < cxt.nrealwriters_stress; i++)
>              torture_stop_kthread(lock_torture_writer,
> @@ -776,6 +785,7 @@ static void lock_torture_cleanup(void)
>      else
>          lock_torture_print_module_parms(cxt.cur_ops,
>                          "End of test: SUCCESS");
> +end:
>      torture_cleanup_end();
>  }
>  
> @@ -878,6 +888,7 @@ static int __init lock_torture_init(void)
>              cxt.lrsa[i].n_lock_acquired = 0;
>          }
>      }
> +
>      lock_torture_print_module_parms(cxt.cur_ops, "Start of test");
>  
>      /* Prepare torture context. */