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Subject[PATCH] debugobjects: fix lockdep warning #2
From
On Thu, Aug 28, 2008 at 3:56 PM, Ingo Molnar <mingo@elte.hu> wrote:
> could you resend the final patch please? It's a candidate for .27, if it
> works out fine.

Here is the combined patch. I've tested it only briefly, and I am
unsure of whether it still produces lockdep warnings for Daniel or
not. I wish it would not be applied anywhere unless it was
officially Reviewed-by: someone. In particular, I'm not quite
steady with the irq-safe locking (Thomas might want to have a look).

Thanks :)


Vegard


From 977cf583b79be7308d5e310711fe6038c8af96a4 Mon Sep 17 00:00:00 2001
From: Vegard Nossum <vegard.nossum@gmail.com>
Date: Thu, 28 Aug 2008 17:09:57 +0200
Subject: [PATCH] debugobjects: fix lockdep warning #2

Daniel J. Blueman reported:
> =======================================================
> [ INFO: possible circular locking dependency detected ]
> 2.6.27-rc4-224c #1
> -------------------------------------------------------
> hald/4680 is trying to acquire lock:
> (&n->list_lock){++..}, at: [<ffffffff802bfa26>] add_partial+0x26/0x80
>
> but task is already holding lock:
> (&obj_hash[i].lock){++..}, at: [<ffffffff8041cfdc>]
> debug_object_free+0x5c/0x120

We fix it by moving the actual freeing to outside the lock (the lock
now only protects the list).

The lock is also promoted to irq-safe (suggested by Dan).

Reported-by: Daniel J Blueman <daniel.blueman@gmail.com>
Signed-off-by: Vegard Nossum <vegard.nossum@gmail.com>
---
lib/debugobjects.c | 38 +++++++++++++++++++++++++++++---------
1 files changed, 29 insertions(+), 9 deletions(-)
diff --git a/lib/debugobjects.c b/lib/debugobjects.c
index 19acf8c..acf9ed8 100644
--- a/lib/debugobjects.c
+++ b/lib/debugobjects.c
@@ -115,9 +115,10 @@ static struct debug_obj *lookup_object(void *addr, struct debug_bucket *b)
static struct debug_obj *
alloc_object(void *addr, struct debug_bucket *b, struct debug_obj_descr *descr)
{
+ unsigned long flags;
struct debug_obj *obj = NULL;

- spin_lock(&pool_lock);
+ spin_lock_irqsave(&pool_lock, flags);
if (obj_pool.first) {
obj = hlist_entry(obj_pool.first, typeof(*obj), node);

@@ -136,7 +137,7 @@ alloc_object(void *addr, struct debug_bucket *b, struct debug_obj_descr *descr)
if (obj_pool_free < obj_pool_min_free)
obj_pool_min_free = obj_pool_free;
}
- spin_unlock(&pool_lock);
+ spin_unlock_irqrestore(&pool_lock, flags);

return obj;
}
@@ -146,18 +147,19 @@ alloc_object(void *addr, struct debug_bucket *b, struct debug_obj_descr *descr)
*/
static void free_object(struct debug_obj *obj)
{
+ unsigned long flags;
unsigned long idx = (unsigned long)(obj - obj_static_pool);

if (obj_pool_free < ODEBUG_POOL_SIZE || idx < ODEBUG_POOL_SIZE) {
- spin_lock(&pool_lock);
+ spin_lock_irqsave(&pool_lock, flags);
hlist_add_head(&obj->node, &obj_pool);
obj_pool_free++;
obj_pool_used--;
- spin_unlock(&pool_lock);
+ spin_unlock_irqrestore(&pool_lock, flags);
} else {
- spin_lock(&pool_lock);
+ spin_lock_irqsave(&pool_lock, flags);
obj_pool_used--;
- spin_unlock(&pool_lock);
+ spin_unlock_irqrestore(&pool_lock, flags);
kmem_cache_free(obj_cache, obj);
}
}
@@ -170,19 +172,28 @@ static void debug_objects_oom(void)
{
struct debug_bucket *db = obj_hash;
struct hlist_node *node, *tmp;
+ HLIST_HEAD(freelist);
struct debug_obj *obj;
unsigned long flags;
int i;

printk(KERN_WARNING "ODEBUG: Out of memory. ODEBUG disabled\n");

+ /* XXX: Could probably be optimized by transplantation of more than
+ * one entry at a time. */
for (i = 0; i < ODEBUG_HASH_SIZE; i++, db++) {
spin_lock_irqsave(&db->lock, flags);
hlist_for_each_entry_safe(obj, node, tmp, &db->list, node) {
hlist_del(&obj->node);
- free_object(obj);
+ hlist_add_head(&obj->node, &freelist);
}
spin_unlock_irqrestore(&db->lock, flags);
+
+ /* Now free them */
+ hlist_for_each_entry_safe(obj, node, tmp, &freelist, node) {
+ hlist_del(&obj->node);
+ free_object(obj);
+ }
}
}

@@ -500,8 +511,9 @@ void debug_object_free(void *addr, struct debug_obj_descr *descr)
return;
default:
hlist_del(&obj->node);
+ spin_unlock_irqrestore(&db->lock, flags);
free_object(obj);
- break;
+ return;
}
out_unlock:
spin_unlock_irqrestore(&db->lock, flags);
@@ -512,6 +524,7 @@ static void __debug_check_no_obj_freed(const void *address, unsigned long size)
{
unsigned long flags, oaddr, saddr, eaddr, paddr, chunks;
struct hlist_node *node, *tmp;
+ HLIST_HEAD(freelist);
struct debug_obj_descr *descr;
enum debug_obj_state state;
struct debug_bucket *db;
@@ -547,11 +560,18 @@ repeat:
goto repeat;
default:
hlist_del(&obj->node);
- free_object(obj);
+ hlist_add_head(&obj->node, &freelist);
break;
}
}
spin_unlock_irqrestore(&db->lock, flags);
+
+ /* Now free them */
+ hlist_for_each_entry_safe(obj, node, tmp, &freelist, node) {
+ hlist_del(&obj->node);
+ free_object(obj);
+ }
+
if (cnt > debug_objects_maxchain)
debug_objects_maxchain = cnt;
}
--
1.5.5.1


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