[PATCH] debugobjects: fix lockdep warning #2

[PATCH] debugobjects: fix lockdep warning #2

[Vegard Nossum]

On Thu, Aug 28, 2008 at 3:56 PM, Ingo Molnar <mingo-X9Un+BFzKDI@public.gmane.org> 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-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
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-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
Signed-off-by: Vegard Nossum <vegard.nossum-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
---
 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

Re: [PATCH] debugobjects: fix lockdep warning #2

[Andrew Morton]

On Thu, 28 Aug 2008 17:32:14 +0200
Vegard Nossum <vegard.nossum-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:

> On Thu, Aug 28, 2008 at 3:56 PM, Ingo Molnar <mingo-X9Un+BFzKDI@public.gmane.org> 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).
> 

It all looks good to me.

> 
> 
> >From 977cf583b79be7308d5e310711fe6038c8af96a4 Mon Sep 17 00:00:00 2001
> From: Vegard Nossum <vegard.nossum-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
> 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).

What was the reason for this other change?  I'm sure Dan is a fine chap,
but we usually prefer a little more justification for changes ;)

> Reported-by: Daniel J Blueman <daniel.blueman-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
> Signed-off-by: Vegard Nossum <vegard.nossum-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
> ---
>  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);

I suspect that we can avoid the hlist_del() here, perhaps with a little
effort.

> +
> +		/* Now free them */
> +		hlist_for_each_entry_safe(obj, node, tmp, &freelist, node) {
> +			hlist_del(&obj->node);
> +			free_object(obj);
> +		}
> +

and the other one.

But I'm not sure that it's worth putting effort into - leaving dead
objects strung onto a partially-live list is a little bit smelly IMO.

Re: [PATCH] debugobjects: fix lockdep warning #2

[Thomas Gleixner]

On Thu, 28 Aug 2008, Andrew Morton wrote:
> > 
> > The lock is also promoted to irq-safe (suggested by Dan).
> 
> What was the reason for this other change?  I'm sure Dan is a fine chap,
> but we usually prefer a little more justification for changes ;)

I added the info already, when I applied it to the tip-tree.

> > +		/* Now free them */
> > +		hlist_for_each_entry_safe(obj, node, tmp, &freelist, node) {
> > +			hlist_del(&obj->node);
> > +			free_object(obj);
> 
> I suspect that we can avoid the hlist_del() here, perhaps with a little
> effort.
> 
> > +
> > +		/* Now free them */
> > +		hlist_for_each_entry_safe(obj, node, tmp, &freelist, node) {
> > +			hlist_del(&obj->node);
> > +			free_object(obj);
> > +		}
> > +
> 
> and the other one.
> 
> But I'm not sure that it's worth putting effort into - leaving dead
> objects strung onto a partially-live list is a little bit smelly IMO.

I really feel better, when we delete them instead of throwing them
away with pointers to each other.

Thanks,

	tglx

Re: [PATCH] debugobjects: fix lockdep warning #2

[Daniel J Blueman]

Hi Andrew, Vegard, Ingo,

On Fri, Aug 29, 2008 at 1:17 AM, Andrew Morton
<akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org> wrote:
> On Thu, 28 Aug 2008 17:32:14 +0200
> Vegard Nossum <vegard.nossum-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
>
>> On Thu, Aug 28, 2008 at 3:56 PM, Ingo Molnar <mingo-X9Un+BFzKDI@public.gmane.org> 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).
>>
>
> It all looks good to me.
>
>>
>>
>> >From 977cf583b79be7308d5e310711fe6038c8af96a4 Mon Sep 17 00:00:00 2001
>> From: Vegard Nossum <vegard.nossum-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
>> 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).
>
> What was the reason for this other change?  I'm sure Dan is a fine chap,
> but we usually prefer a little more justification for changes ;)

IRQ-safe xtime_lock is taken, then pool_lock is taken in
__debug_object_init, which is potentially unsafe. Upgrading
pool_lock's usage to IRQ-safe ensures there can be no potential for
deadlock.

>> Reported-by: Daniel J Blueman <daniel.blueman-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
>> Signed-off-by: Vegard Nossum <vegard.nossum-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
>> ---
>>  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);
>
> I suspect that we can avoid the hlist_del() here, perhaps with a little
> effort.
>
>> +
>> +             /* Now free them */
>> +             hlist_for_each_entry_safe(obj, node, tmp, &freelist, node) {
>> +                     hlist_del(&obj->node);
>> +                     free_object(obj);
>> +             }
>> +
>
> and the other one.
>
> But I'm not sure that it's worth putting effort into - leaving dead
> objects strung onto a partially-live list is a little bit smelly IMO.

I've done some fairly heavy testing with the patch at it's current
state (ie with the upgraded pool_lock, explained above), and it _is_
in fact solid; I wasn't looking at the right setup previously.

(with the other XFS tweaks too) I'm not able to cause any
deadlocks/stack traces/warnings with maximum debugging [* the KVM
errors are another story], which would be the first time so far, so
the patch looks good for mainline and 2.6.27 is looking very strong!

Daniel

--- [*]

emulation failed (pagetable) rip bf9032c5 0f 6f 17 0f
__ratelimit: 1804664 callbacks suppressed
Fail to handle apic access vmexit! Offset is 0xf0
-- 
Daniel J Blueman

[GIT pull] debugobject fixes for 2.6.27

[Thomas Gleixner]

Linus,

Please pull the latest core/debugobjects git tree from:

   git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip.git core/debugobjects

It contains a lockdep fix for the debug objects core code. Please note
that I added a helper function to move a hlist from one head to
another to avoid open coding it in the debugobjects code.

 Thanks,

	tglx

------------------>
Vegard Nossum (1):
      debugobjects: fix lockdep warning


 include/linux/list.h |   13 +++++++++++++
 lib/debugobjects.c   |   31 +++++++++++++++++++++++--------
 2 files changed, 36 insertions(+), 8 deletions(-)

diff --git a/include/linux/list.h b/include/linux/list.h
index db35ef0..969f6e9 100644
--- a/include/linux/list.h
+++ b/include/linux/list.h
@@ -619,6 +619,19 @@ static inline void hlist_add_after(struct hlist_node *n,
 		next->next->pprev  = &next->next;
 }
 
+/*
+ * Move a list from one list head to another. Fixup the pprev
+ * reference of the first entry if it exists.
+ */
+static inline void hlist_move_list(struct hlist_head *old,
+				   struct hlist_head *new)
+{
+	new->first = old->first;
+	if (new->first)
+		new->first->pprev = &new->first;
+	old->first = NULL;
+}
+
 #define hlist_entry(ptr, type, member) container_of(ptr,type,member)
 
 #define hlist_for_each(pos, head) \
diff --git a/lib/debugobjects.c b/lib/debugobjects.c
index 45a6bde..e3ab374 100644
--- a/lib/debugobjects.c
+++ b/lib/debugobjects.c
@@ -112,6 +112,7 @@ static struct debug_obj *lookup_object(void *addr, struct debug_bucket *b)
 
 /*
  * Allocate a new object. If the pool is empty, switch off the debugger.
+ * Must be called with interrupts disabled.
  */
 static struct debug_obj *
 alloc_object(void *addr, struct debug_bucket *b, struct debug_obj_descr *descr)
@@ -148,17 +149,18 @@ alloc_object(void *addr, struct debug_bucket *b, struct debug_obj_descr *descr)
 static void free_object(struct debug_obj *obj)
 {
 	unsigned long idx = (unsigned long)(obj - obj_static_pool);
+	unsigned long flags;
 
 	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);
 	}
 }
@@ -171,6 +173,7 @@ 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;
@@ -179,11 +182,14 @@ static void debug_objects_oom(void)
 
 	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_move_list(&db->list, &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);
 		}
-		spin_unlock_irqrestore(&db->lock, flags);
 	}
 }
 
@@ -498,8 +504,9 @@ 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);
@@ -510,6 +517,7 @@ 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;
@@ -545,11 +553,18 @@ 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;
 	}

Re: [PATCH] debugobjects: fix lockdep warning #2

[Thomas Gleixner]

On Thu, 28 Aug 2008, Vegard Nossum wrote:
> On Thu, Aug 28, 2008 at 3:56 PM, Ingo Molnar <mingo-X9Un+BFzKDI@public.gmane.org> 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).

The irq safe locking is the easy part :) Calling free_object w/o the
hash bucket lock held is fine as we removed it already from the bucket
and there is no other reference than the pointer we hold at that point.
 
>  
>  	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);
> +		}
>  	}
>  }

What you want is a helper function which moves the complete list from
one head to the other. I'll whip one up.

I'll push it through the tip tree.

Thanks,

	tglx