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Subject[PATCH V2] lockdep: reduce stack_trace usage
From 04395389820e89c0bd4bb57b939ec1882e0bb5da Mon Sep 17 00:00:00 2001
From: Yong Zhang <yong.zhang@windriver.com>
Date: Tue, 4 May 2010 14:16:48 +0800
Subject: [PATCH] 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.
Using 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: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: David S. Miller <davem@davemloft.net>
---
kernel/lockdep.c | 22 ++++++++++++++--------
1 files changed, 14 insertions(+), 8 deletions(-)

diff --git a/kernel/lockdep.c b/kernel/lockdep.c
index 2594e1c..56e0ff9 100644
--- a/kernel/lockdep.c
+++ b/kernel/lockdep.c
@@ -818,7 +818,8 @@ 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;
/*
@@ -829,11 +830,9 @@ 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
@@ -1635,12 +1634,13 @@ 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 struct stack_trace trace;

/*
* Prove that the new <prev> -> <next> dependency would not
@@ -1688,20 +1688,23 @@ 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;

@@ -1731,6 +1734,7 @@ 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;

/*
@@ -1756,7 +1760,8 @@ 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,
@@ -1779,6 +1784,7 @@ 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:
--
1.6.3.3


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