linux-kernel - Re: [PATCH -tip] x86: uv - prevent NULL dereference in uv_system

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Message-ID: <20090503121228.GC4615@lenovo>
Date:	Sun, 3 May 2009 16:12:28 +0400
From:	Cyrill Gorcunov <gorcunov@...il.com>
To:	Pekka Enberg <penberg@...helsinki.fi>
Cc:	David Rientjes <rientjes@...gle.com>, Ingo Molnar <mingo@...e.hu>,
	Jack Steiner <steiner@....com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH -tip] x86: uv - prevent NULL dereference in
	uv_system_init

[Pekka Enberg - Sun, May 03, 2009 at 12:59:13PM +0300]
| Hi David,
| 
| On Sun, May 3, 2009 at 12:09 PM, David Rientjes <rientjes@...gle.com> wrote:
| > SLUB stores two new slab allocation orders: the cache's adjustable order
| > which is calculated at kmem_cache_create(), and the smallest order that
| > can accommodate at least one object allocation.  The latter is used as a
| > fallback when the former fails in the page allocator.
| >
| > So for __GFP_PANIC to work in this case, it could not be implemented in
| > the page allocator (SLUB also passes __GFP_NORETRY for new slabs) but
| > rather above it in allocate_slab().  It would then be a no-op for
| > alloc_pages().
| 
| It's probably better to implement __GFP_PANIC in alloc_pages() because
| of kmalloc_large(). You can easily mask the __GFP_PANIC from the first
| call to alloc_slab_page() where we use __GFP_NOWARN to suppress
| out-of-memory warnings.
| 
| But anyway, enough talk, show me the patch! :-)
| 
|                                           Pekka
| 

I was thinking about the approach showed below.

Note even if we will agree on this idea a number
of questions remain opened -- like where is a better
place to define kmalloc_panic in slub/slab_def.h
or rather in slab.h. Should we include kernel.h
to have panic and pr_ properly defined?

I don't dare start/introduce handling of __GFP_PANIC
flag since it would require more efforts to be done
correctly and what is more important -- for most
cases we would just don't need it.

	-- Cyrill

---
 include/linux/slab_def.h |   12 ++++++++++++
 1 file changed, 12 insertions(+)

Index: linux-2.6.git/include/linux/slab_def.h
=====================================================================
--- linux-2.6.git.orig/include/linux/slab_def.h
+++ linux-2.6.git/include/linux/slab_def.h
@@ -220,4 +220,16 @@ found:

 #endif	/* CONFIG_NUMA */

+static inline void *kmalloc_panic(size_t size, gfp_t flags)
+{
+	void *p = kmalloc(size, flags);
+
+	if (size && ZERO_OR_NULL_PTR(p)) {
+		pr_emerg("Failed to allocate: %z bytes\n", size);
+		panic("Out of memory\n");
+	}
+
+	return p;
+}
+
 #endif	/* _LINUX_SLAB_DEF_H */
--
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