Re: [PATCH v8 06/14] lockdep: Detect and handle hist_lock ring buffer overwrite

[Boqun Feng]

On Mon, Aug 07, 2017 at 04:12:53PM +0900, Byungchul Park wrote:
> The ring buffer can be overwritten by hardirq/softirq/work contexts.
> That cases must be considered on rollback or commit. For example,
> 
>           |<------ hist_lock ring buffer size ----->|
>           ppppppppppppiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii
> wrapped > iiiiiiiiiiiiiiiiiiiiiii....................
> 
>           where 'p' represents an acquisition in process context,
>           'i' represents an acquisition in irq context.
> 
> On irq exit, crossrelease tries to rollback idx to original position,
> but it should not because the entry already has been invalid by
> overwriting 'i'. Avoid rollback or commit for entries overwritten.
> 
> Signed-off-by: Byungchul Park <byungchul.park@xxxxxxx>
> ---
>  include/linux/lockdep.h  | 20 +++++++++++++++++++
>  include/linux/sched.h    |  3 +++
>  kernel/locking/lockdep.c | 52 +++++++++++++++++++++++++++++++++++++++++++-----
>  3 files changed, 70 insertions(+), 5 deletions(-)
> 
> diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h
> index 0c8a1b8..48c244c 100644
> --- a/include/linux/lockdep.h
> +++ b/include/linux/lockdep.h
> @@ -284,6 +284,26 @@ struct held_lock {
>   */
>  struct hist_lock {
>  	/*
> +	 * Id for each entry in the ring buffer. This is used to
> +	 * decide whether the ring buffer was overwritten or not.
> +	 *
> +	 * For example,
> +	 *
> +	 *           |<----------- hist_lock ring buffer size ------->|
> +	 *           pppppppppppppppppppppiiiiiiiiiiiiiiiiiiiiiiiiiiiii
> +	 * wrapped > iiiiiiiiiiiiiiiiiiiiiiiiiii.......................
> +	 *
> +	 *           where 'p' represents an acquisition in process
> +	 *           context, 'i' represents an acquisition in irq
> +	 *           context.
> +	 *
> +	 * In this example, the ring buffer was overwritten by
> +	 * acquisitions in irq context, that should be detected on
> +	 * rollback or commit.
> +	 */
> +	unsigned int hist_id;
> +
> +	/*
>  	 * Seperate stack_trace data. This will be used at commit step.
>  	 */
>  	struct stack_trace	trace;
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index 5becef5..373466b 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -855,6 +855,9 @@ struct task_struct {
>  	unsigned int xhlock_idx;
>  	/* For restoring at history boundaries */
>  	unsigned int xhlock_idx_hist[CONTEXT_NR];
> +	unsigned int hist_id;
> +	/* For overwrite check at each context exit */
> +	unsigned int hist_id_save[CONTEXT_NR];
>  #endif
>  
>  #ifdef CONFIG_UBSAN
> diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
> index afd6e64..5168dac 100644
> --- a/kernel/locking/lockdep.c
> +++ b/kernel/locking/lockdep.c
> @@ -4742,6 +4742,17 @@ void lockdep_rcu_suspicious(const char *file, const int line, const char *s)
>  static atomic_t cross_gen_id; /* Can be wrapped */
>  
>  /*
> + * Make an entry of the ring buffer invalid.
> + */
> +static inline void invalidate_xhlock(struct hist_lock *xhlock)
> +{
> +	/*
> +	 * Normally, xhlock->hlock.instance must be !NULL.
> +	 */
> +	xhlock->hlock.instance = NULL;
> +}
> +
> +/*
>   * Lock history stacks; we have 3 nested lock history stacks:
>   *
>   *   Hard IRQ
> @@ -4773,14 +4784,28 @@ void lockdep_rcu_suspicious(const char *file, const int line, const char *s)
>   */
>  void crossrelease_hist_start(enum context_t c)
>  {
> -	if (current->xhlocks)
> -		current->xhlock_idx_hist[c] = current->xhlock_idx;
> +	struct task_struct *cur = current;
> +
> +	if (cur->xhlocks) {
> +		cur->xhlock_idx_hist[c] = cur->xhlock_idx;
> +		cur->hist_id_save[c] = cur->hist_id;
> +	}
>  }
>  
>  void crossrelease_hist_end(enum context_t c)
>  {
> -	if (current->xhlocks)
> -		current->xhlock_idx = current->xhlock_idx_hist[c];
> +	struct task_struct *cur = current;
> +
> +	if (cur->xhlocks) {
> +		unsigned int idx = cur->xhlock_idx_hist[c];
> +		struct hist_lock *h = &xhlock(idx);
> +
> +		cur->xhlock_idx = idx;
> +
> +		/* Check if the ring was overwritten. */
> +		if (h->hist_id != cur->hist_id_save[c])

Could we use:

		if (h->hist_id != idx)

here, and

> +			invalidate_xhlock(h);
> +	}
>  }
>  
>  static int cross_lock(struct lockdep_map *lock)
> @@ -4826,6 +4851,7 @@ static inline int depend_after(struct held_lock *hlock)
>   * Check if the xhlock is valid, which would be false if,
>   *
>   *    1. Has not used after initializaion yet.
> + *    2. Got invalidated.
>   *
>   * Remind hist_lock is implemented as a ring buffer.
>   */
> @@ -4857,6 +4883,7 @@ static void add_xhlock(struct held_lock *hlock)
>  
>  	/* Initialize hist_lock's members */
>  	xhlock->hlock = *hlock;
> +	xhlock->hist_id = current->hist_id++;

use:

	xhlock->hist_id = idx;

and,


>  
>  	xhlock->trace.nr_entries = 0;
>  	xhlock->trace.max_entries = MAX_XHLOCK_TRACE_ENTRIES;
> @@ -4995,6 +5022,7 @@ static int commit_xhlock(struct cross_lock *xlock, struct hist_lock *xhlock)
>  static void commit_xhlocks(struct cross_lock *xlock)
>  {
>  	unsigned int cur = current->xhlock_idx;
> +	unsigned int prev_hist_id = xhlock(cur).hist_id;

use:
	unsigned int prev_hist_id = cur;

here.

Then we can get away with the added fields in task_struct at least.

Thought?

Regards,
Boqun

>  	unsigned int i;
>  
>  	if (!graph_lock())
> @@ -5013,6 +5041,17 @@ static void commit_xhlocks(struct cross_lock *xlock)
>  			break;
>  
>  		/*
> +		 * Filter out the cases that the ring buffer was
> +		 * overwritten and the previous entry has a bigger
> +		 * hist_id than the following one, which is impossible
> +		 * otherwise.
> +		 */
> +		if (unlikely(before(xhlock->hist_id, prev_hist_id)))
> +			break;
> +
> +		prev_hist_id = xhlock->hist_id;
> +
> +		/*
>  		 * commit_xhlock() returns 0 with graph_lock already
>  		 * released if fail.
>  		 */
> @@ -5085,9 +5124,12 @@ void lockdep_init_task(struct task_struct *task)
>  	int i;
>  
>  	task->xhlock_idx = UINT_MAX;
> +	task->hist_id = 0;
>  
> -	for (i = 0; i < CONTEXT_NR; i++)
> +	for (i = 0; i < CONTEXT_NR; i++) {
>  		task->xhlock_idx_hist[i] = UINT_MAX;
> +		task->hist_id_save[i] = 0;
> +	}
>  
>  	task->xhlocks = kzalloc(sizeof(struct hist_lock) * MAX_XHLOCKS_NR,
>  				GFP_KERNEL);
> -- 
> 1.9.1
>

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