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lockdep: Reduce stack_trace usage

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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: Yong Zhang <yong.zhang0@windriver.com>
Cc: David S. Miller <davem@davemloft.net>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <20100504065711.GC10784@windriver.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Yong Zhang 2010-05-04 14:16:48 +08:00 committed by Ingo Molnar
parent 54d47a2be5
commit 4726f2a617
1 changed files with 21 additions and 8 deletions
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29
kernel/lockdep.c
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@ -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: