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

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Message-ID: <20090503093814.GB4615@lenovo>
Date:	Sun, 3 May 2009 13:38:14 +0400
From:	Cyrill Gorcunov <gorcunov@...il.com>
To:	David Rientjes <rientjes@...gle.com>
Cc:	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

[David Rientjes - Sun, May 03, 2009 at 02:09:50AM -0700]
| On Sun, 3 May 2009, Ingo Molnar wrote:
| 
| > Hm, would be nice if we had a __GFP_PANIC variant in kmalloc that 
| > would just panic straight in the allocator, when allocation failure 
| > is not acceptable. (Andrew Cc:-ed)
| > 
| > It does not increase the priority of the allocation nor does it 
| > trigger any 'dont fail' logic - it is simply the central expression 
| > of 'this should not have failed, panic'.
| > 
| 
| 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().
| 

What if instead of tear thru all these cases we implement
a special wrapper (say kmalloc_panic)? Almost the same
are done for bootmem allocator (__alloc_bootmem_nopanic).

It seems __GFP_PANIC would not be that popular anyway
and what is more important -- we would add additional
check the flag somewhere inside mm code (which will
be not needed most the time).

	-- Cyrill
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