Re: WARNING: kmemcheck: Caught 32-bit read from uninitialized memory (f6f6e1a4), by kmemleak's scan_block()

[Pekka Enberg <penberg@cs.helsinki.fi>]

On Tue, 2009-08-25 at 10:32 +0200, Ingo Molnar wrote:
> > In any case, I don't think it is very productive to run them both 
> > at the same time, simply because kmemcheck slows every memory 
> > access down so much and scanning memory doesn't exactly help that. 
> > It _could_ be useful to have them compiled into the same kernel, 
> > though, e.g. a distro "-debug" kernel.
> > 
> > Maybe you can just add the "depends on !KMEMLEAK" to 
> > CONFIG_KMEMCHECK in tip/out-of-tree for now?
> 
> i think it would be far more intelligent to annotate those accesses 
> by kmemleak as 'trust me, dont check'. Willing to test such a patch.

I guess something like this totally untested patch should do it. Vegard,
Catalin?

			Pekka

diff --git a/arch/x86/mm/kmemcheck/kmemcheck.c b/arch/x86/mm/kmemcheck/kmemcheck.c
index 2c55ed0..528bf95 100644
--- a/arch/x86/mm/kmemcheck/kmemcheck.c
+++ b/arch/x86/mm/kmemcheck/kmemcheck.c
@@ -331,6 +331,20 @@ static void kmemcheck_read_strict(struct pt_regs *regs,
 	kmemcheck_shadow_set(shadow, size);
 }
 
+bool kmemcheck_is_obj_initialized(unsigned long addr, size_t size)
+{
+	enum kmemcheck_shadow status;
+	void *shadow;
+
+	shadow = kmemcheck_shadow_lookup(addr);
+	if (!shadow)
+		return true;
+
+	status = kmemcheck_shadow_test(shadow, size);
+
+	return status == KMEMCHECK_SHADOW_INITIALIZED;
+}
+
 /* Access may cross page boundary */
 static void kmemcheck_read(struct pt_regs *regs,
 	unsigned long addr, unsigned int size)
diff --git a/include/linux/kmemcheck.h b/include/linux/kmemcheck.h
index 47b39b7..dc2fd54 100644
--- a/include/linux/kmemcheck.h
+++ b/include/linux/kmemcheck.h
@@ -34,6 +34,8 @@ void kmemcheck_mark_initialized_pages(struct page *p, unsigned int n);
 int kmemcheck_show_addr(unsigned long address);
 int kmemcheck_hide_addr(unsigned long address);
 
+bool kmemcheck_is_obj_initialized(unsigned long addr, size_t size);
+
 #else
 #define kmemcheck_enabled 0
 
@@ -99,6 +101,11 @@ static inline void kmemcheck_mark_initialized_pages(struct page *p,
 {
 }
 
+static inline bool kmemcheck_is_obj_initialized(unsigned long addr, size_t size)
+{
+	return true;
+}
+
 #endif /* CONFIG_KMEMCHECK */
 
 /*
diff --git a/mm/kmemleak.c b/mm/kmemleak.c
index 4872673..c14d6e4 100644
--- a/mm/kmemleak.c
+++ b/mm/kmemleak.c
@@ -97,6 +97,7 @@
 #include <asm/processor.h>
 #include <asm/atomic.h>
 
+#include <linux/kmemcheck.h>
 #include <linux/kmemleak.h>
 
 /*
@@ -949,6 +950,8 @@ static void scan_object(struct kmemleak_object *object)
 	if (!(object->flags & OBJECT_ALLOCATED))
 		/* already freed object */
 		goto out;
+	if (!kmemcheck_is_obj_initialized(object->pointer, object->size))
+		goto out;
 	if (hlist_empty(&object->area_list))
 		scan_block((void *)object->pointer,
 			   (void *)(object->pointer + object->size), object, 0);