linux-kernel - Re: [PATCH 6/9] torture: Address race in module cleanup

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Message-ID: <20140912180407.GF4775@linux.vnet.ibm.com>
Date:	Fri, 12 Sep 2014 11:04:07 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Davidlohr Bueso <dave@...olabs.net>
Cc:	peterz@...radead.org, mingo@...nel.org,
	linux-kernel@...r.kernel.org, Davidlohr Bueso <dbueso@...e.de>
Subject: Re: [PATCH 6/9] torture: Address race in module cleanup

On Thu, Sep 11, 2014 at 08:40:21PM -0700, Davidlohr Bueso wrote:
> When performing module cleanups by calling torture_cleanup() the
> 'torture_type' string in nullified However, callers are not necessarily
> done, and might still need to reference the variable. This impacts
> both rcutorture and locktorture, causing printing things like:
> 
> [   94.226618] (null)-torture: Stopping lock_torture_writer task
> [   94.226624] (null)-torture: Stopping lock_torture_stats task
> 
> Thus delay this operation until the very end of the cleanup process.
> The consequence (which shouldn't matter for this kid of program) is,
> of course, that we delay the window between rmmod and modprobing,
> for instance in module_torture_begin().
> 
> Signed-off-by: Davidlohr Bueso <dbueso@...e.de>

Good catch!  I had just been ignoring the (null), and my scripting
doesn't care, but it is better to have it taken care of.

							Thanx, Paul

> ---
>  include/linux/torture.h      |  3 ++-
>  kernel/locking/locktorture.c |  3 ++-
>  kernel/rcu/rcutorture.c      |  3 ++-
>  kernel/torture.c             | 16 +++++++++++++---
>  4 files changed, 19 insertions(+), 6 deletions(-)
> 
> diff --git a/include/linux/torture.h b/include/linux/torture.h
> index 5ca58fc..301b628 100644
> --- a/include/linux/torture.h
> +++ b/include/linux/torture.h
> @@ -77,7 +77,8 @@ int torture_stutter_init(int s);
>  /* Initialization and cleanup. */
>  bool torture_init_begin(char *ttype, bool v, int *runnable);
>  void torture_init_end(void);
> -bool torture_cleanup(void);
> +bool torture_cleanup_begin(void);
> +void torture_cleanup_end(void);
>  bool torture_must_stop(void);
>  bool torture_must_stop_irq(void);
>  void torture_kthread_stopping(char *title);
> diff --git a/kernel/locking/locktorture.c b/kernel/locking/locktorture.c
> index de703a7..988267c 100644
> --- a/kernel/locking/locktorture.c
> +++ b/kernel/locking/locktorture.c
> @@ -361,7 +361,7 @@ static void lock_torture_cleanup(void)
>  {
>  	int i;
> 
> -	if (torture_cleanup())
> +	if (torture_cleanup_begin())
>  		return;
> 
>  	if (writer_tasks) {
> @@ -384,6 +384,7 @@ static void lock_torture_cleanup(void)
>  	else
>  		lock_torture_print_module_parms(cur_ops,
>  						"End of test: SUCCESS");
> +	torture_cleanup_end();
>  }
> 
>  static int __init lock_torture_init(void)
> diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
> index 948a769..57a2792 100644
> --- a/kernel/rcu/rcutorture.c
> +++ b/kernel/rcu/rcutorture.c
> @@ -1418,7 +1418,7 @@ rcu_torture_cleanup(void)
>  	int i;
> 
>  	rcutorture_record_test_transition();
> -	if (torture_cleanup()) {
> +	if (torture_cleanup_begin()) {
>  		if (cur_ops->cb_barrier != NULL)
>  			cur_ops->cb_barrier();
>  		return;
> @@ -1468,6 +1468,7 @@ rcu_torture_cleanup(void)
>  					       "End of test: RCU_HOTPLUG");
>  	else
>  		rcu_torture_print_module_parms(cur_ops, "End of test: SUCCESS");
> +	torture_cleanup_end();
>  }
> 
>  #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD
> diff --git a/kernel/torture.c b/kernel/torture.c
> index d600af2..07a5c3d 100644
> --- a/kernel/torture.c
> +++ b/kernel/torture.c
> @@ -635,8 +635,13 @@ EXPORT_SYMBOL_GPL(torture_init_end);
>   *
>   * This must be called before the caller starts shutting down its own
>   * kthreads.
> + *
> + * Both torture_cleanup_begin() and torture_cleanup_end() must be paired,
> + * in order to correctly perform the cleanup. They are separated because
> + * threads can still need to reference the torture_type type, thus nullify
> + * only after completing all other relevant calls.
>   */
> -bool torture_cleanup(void)
> +bool torture_cleanup_begin(void)
>  {
>  	mutex_lock(&fullstop_mutex);
>  	if (ACCESS_ONCE(fullstop) == FULLSTOP_SHUTDOWN) {
> @@ -651,12 +656,17 @@ bool torture_cleanup(void)
>  	torture_shuffle_cleanup();
>  	torture_stutter_cleanup();
>  	torture_onoff_cleanup();
> +	return false;
> +}
> +EXPORT_SYMBOL_GPL(torture_cleanup_begin);
> +
> +void torture_cleanup_end(void)
> +{
>  	mutex_lock(&fullstop_mutex);
>  	torture_type = NULL;
>  	mutex_unlock(&fullstop_mutex);
> -	return false;
>  }
> -EXPORT_SYMBOL_GPL(torture_cleanup);
> +EXPORT_SYMBOL_GPL(torture_cleanup_end);
> 
>  /*
>   * Is it time for the current torture test to stop?
> -- 
> 1.8.4.5
> 

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