Commit 4726f2a6 authored by Yong Zhang's avatar Yong Zhang Committed by Ingo Molnar
Browse files

lockdep: Reduce stack_trace usage 



When calling check_prevs_add(), if all validations passed
add_lock_to_list() will add new lock to dependency tree and
alloc stack_trace for each list_entry.

But at this time, we are always on the same stack, so stack_trace
for each list_entry has the same value. This is redundant and eats
up lots of memory which could lead to warning on low
MAX_STACK_TRACE_ENTRIES.

Use one copy of stack_trace instead.

V2: As suggested by Peter Zijlstra, move save_trace() from
    check_prevs_add() to check_prev_add().
    Add tracking for trylock dependence which is also redundant.

Signed-off-by: default avatarYong Zhang <yong.zhang0@windriver.com>
Cc: David S. Miller <davem@davemloft.net>
Signed-off-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <20100504065711.GC10784@windriver.com>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent 54d47a2b

kernel/lockdep.c

+21 −8
Original line number Diff line number Diff line
@@ -805,7 +805,8 @@ static struct lock_list *alloc_list_entry(void) 
 * Add a new dependency to the head of the list:

 */

static int add_lock_to_list(struct lock_class *class, struct lock_class *this,

			    struct list_head *head, unsigned long ip, int distance)

			    struct list_head *head, unsigned long ip,

			    int distance, struct stack_trace *trace)

{

	struct lock_list *entry;

	/*
@@ -816,11 +817,9 @@ static int add_lock_to_list(struct lock_class *class, struct lock_class *this, 
	if (!entry)

		return 0;



	if (!save_trace(&entry->trace))

		return 0;



	entry->class = this;

	entry->distance = distance;

	entry->trace = *trace;

	/*

	 * Since we never remove from the dependency list, the list can

	 * be walked lockless by other CPUs, it's only allocation
@@ -1622,12 +1621,20 @@ check_deadlock(struct task_struct *curr, struct held_lock *next, 
 */

static int

check_prev_add(struct task_struct *curr, struct held_lock *prev,

	       struct held_lock *next, int distance)

	       struct held_lock *next, int distance, int trylock_loop)

{

	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
@@ -1675,20 +1682,23 @@ check_prev_add(struct task_struct *curr, struct held_lock *prev, 
		}

	}



	if (!trylock_loop && !save_trace(&trace))

		return 0;



	/*

	 * 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);

			       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);

			       next->acquire_ip, distance, &trace);

	if (!ret)

		return 0;
@@ -1718,6 +1728,7 @@ static int 
check_prevs_add(struct task_struct *curr, struct held_lock *next)

{

	int depth = curr->lockdep_depth;

	int trylock_loop = 0;

	struct held_lock *hlock;



	/*
@@ -1743,7 +1754,8 @@ check_prevs_add(struct task_struct *curr, struct held_lock *next) 
		 * added:

		 */

		if (hlock->read != 2) {

			if (!check_prev_add(curr, hlock, next, distance))

			if (!check_prev_add(curr, hlock, next,

						distance, trylock_loop))

				return 0;

			/*

			 * Stop after the first non-trylock entry,
@@ -1766,6 +1778,7 @@ check_prevs_add(struct task_struct *curr, struct held_lock *next) 
		if (curr->held_locks[depth].irq_context !=

				curr->held_locks[depth-1].irq_context)

			break;

		trylock_loop = 1;

	}

	return 1;

out_bug:

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