linux-kernel - Re: [PATCH] lockdep: Make a stack_trace instance passed to check_prev

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Date:   Fri, 13 Jan 2017 13:38:12 +0900
From:   Byungchul Park <byungchul.park@....com>
To:     peterz@...radead.org, mingo@...nel.org
Cc:     linux-kernel@...r.kernel.org
Subject: Re: [PATCH] lockdep: Make a stack_trace instance passed to
 check_prev_add as an arg

On Fri, Jan 13, 2017 at 01:09:41PM +0900, Byungchul Park wrote:
> Like this. Right?

Ignore this. We need to make save_trace work in different way first.

> 
> ----->8-----
> >From c6173f29ff9bf801649f3cbeb80a914fdf1b998b Mon Sep 17 00:00:00 2001
> From: Byungchul Park <byungchul.park@....com>
> Date: Fri, 13 Jan 2017 12:02:02 +0900
> Subject: [PATCH] lockdep: Make a stack_trace instance passed to check_prev_add
>  as an arg
> 
> Saving stack_trace within check_prev_add needs many tricky codes. To
> avoid these, this patch makes the stack_trace instance created out of
> check_prev_add, but by caller and passed as an argument.
> 
> Signed-off-by: Byungchul Park <byungchul.park@....com>
> ---
>  kernel/locking/lockdep.c | 30 +++++++++---------------------
>  1 file changed, 9 insertions(+), 21 deletions(-)
> 
> diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
> index 2081c31..049fc71 100644
> --- a/kernel/locking/lockdep.c
> +++ b/kernel/locking/lockdep.c
> @@ -1797,20 +1797,13 @@ static inline void inc_chains(void)
>   */
>  static int
>  check_prev_add(struct task_struct *curr, struct held_lock *prev,
> -	       struct held_lock *next, int distance, int *stack_saved)
> +	       struct held_lock *next, int distance,
> +	       struct stack_trace *trace)
>  {
>  	struct lock_list *entry;
>  	int ret;
>  	struct lock_list this;
>  	struct lock_list *uninitialized_var(target_entry);
> -	/*
> -	 * Static variable, serialized by the graph_lock().
> -	 *
> -	 * We use this static variable to save the stack trace in case
> -	 * we call into this function multiple times due to encountering
> -	 * trylocks in the held lock stack.
> -	 */
> -	static struct stack_trace trace;
>  
>  	/*
>  	 * Prove that the new <prev> -> <next> dependency would not
> @@ -1858,26 +1851,20 @@ static inline void inc_chains(void)
>  		}
>  	}
>  
> -	if (!*stack_saved) {
> -		if (!save_trace(&trace))
> -			return 0;
> -		*stack_saved = 1;
> -	}
> -
>  	/*
>  	 * Ok, all validations passed, add the new lock
>  	 * to the previous lock's dependency list:
>  	 */
>  	ret = add_lock_to_list(hlock_class(prev), hlock_class(next),
>  			       &hlock_class(prev)->locks_after,
> -			       next->acquire_ip, distance, &trace);
> +			       next->acquire_ip, distance, trace);
>  
>  	if (!ret)
>  		return 0;
>  
>  	ret = add_lock_to_list(hlock_class(next), hlock_class(prev),
>  			       &hlock_class(next)->locks_before,
> -			       next->acquire_ip, distance, &trace);
> +			       next->acquire_ip, distance, trace);
>  	if (!ret)
>  		return 0;
>  
> @@ -1885,8 +1872,6 @@ static inline void inc_chains(void)
>  	 * Debugging printouts:
>  	 */
>  	if (verbose(hlock_class(prev)) || verbose(hlock_class(next))) {
> -		/* We drop graph lock, so another thread can overwrite trace. */
> -		*stack_saved = 0;
>  		graph_unlock();
>  		printk("\n new dependency: ");
>  		print_lock_name(hlock_class(prev));
> @@ -1909,8 +1894,8 @@ static inline void inc_chains(void)
>  check_prevs_add(struct task_struct *curr, struct held_lock *next)
>  {
>  	int depth = curr->lockdep_depth;
> -	int stack_saved = 0;
>  	struct held_lock *hlock;
> +	struct stack_trace trace;
>  
>  	/*
>  	 * Debugging checks.
> @@ -1927,6 +1912,9 @@ static inline void inc_chains(void)
>  			curr->held_locks[depth-1].irq_context)
>  		goto out_bug;
>  
> +	if (!save_trace(&trace))
> +		return 0;
> +
>  	for (;;) {
>  		int distance = curr->lockdep_depth - depth + 1;
>  		hlock = curr->held_locks + depth - 1;
> @@ -1936,7 +1924,7 @@ static inline void inc_chains(void)
>  		 */
>  		if (hlock->read != 2 && hlock->check) {
>  			if (!check_prev_add(curr, hlock, next,
> -						distance, &stack_saved))
> +						distance, &trace))
>  				return 0;
>  			/*
>  			 * Stop after the first non-trylock entry,
> -- 
> 1.9.1