linux-kernel - Re: [slubllv6 12/17] slub: Avoid disabling interrupts in free slowpath

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Date:	Tue, 31 May 2011 12:12:57 -0500 (CDT)
From:	Christoph Lameter <cl@...ux.com>
To:	David Rientjes <rientjes@...gle.com>
cc:	Pekka Enberg <penberg@...helsinki.fi>,
	Eric Dumazet <eric.dumazet@...il.com>,
	"H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [slubllv6 12/17] slub: Avoid disabling interrupts in free
 slowpath

On Thu, 26 May 2011, David Rientjes wrote:

> We know that flags will be initialized at this point in the code, but the
> compiler doesn't and it emits this:
>
> 	mm/slub.c: In function ‘__slab_free’:
> 	mm/slub.c:2198: warning: ‘flags’ may be used uninitialized in this function
>
> so it'll need uninitialized_var().



Subject: slub: Disable interrupts in free_debug processing

We will be calling free_debug_processing with interrupts disabled
in some case when the later patches are applied. Some of the
functions called by free_debug_processing expect interrupts to be
off.

Signed-off-by: Christoph Lameter <cl@...ux.com>


---
 mm/slub.c |   14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

Index: linux-2.6/mm/slub.c
===================================================================
--- linux-2.6.orig/mm/slub.c	2011-05-31 10:20:05.472975031 -0500
+++ linux-2.6/mm/slub.c	2011-05-31 10:20:09.792975006 -0500
@@ -1040,6 +1040,10 @@ bad:
 static noinline int free_debug_processing(struct kmem_cache *s,
 		 struct page *page, void *object, unsigned long addr)
 {
+	unsigned long flags;
+	int rc = 0;
+
+	local_irq_save(flags);
 	slab_lock(page);

 	if (!check_slab(s, page))
@@ -1056,7 +1060,7 @@ static noinline int free_debug_processin
 	}

 	if (!check_object(s, page, object, SLUB_RED_ACTIVE))
-		return 0;
+		goto out;

 	if (unlikely(s != page->slab)) {
 		if (!PageSlab(page)) {
@@ -1077,13 +1081,15 @@ static noinline int free_debug_processin
 		set_track(s, object, TRACK_FREE, addr);
 	trace(s, page, object, 0);
 	init_object(s, object, SLUB_RED_INACTIVE);
+	rc = 1;
+out:
 	slab_unlock(page);
-	return 1;
+	local_irq_restore(flags);
+	return rc;

 fail:
 	slab_fix(s, "Object at 0x%p not freed", object);
-	slab_unlock(page);
-	return 0;
+	goto out;
 }


 static int __init setup_slub_debug(char *str)