linux-kernel - Re: [PATCH] slub: Disable the lockless allocator

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Date:	Sat, 26 Mar 2011 14:30:33 -0500 (CDT)
From:	Christoph Lameter <cl@...ux.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
cc:	Ingo Molnar <mingo@...e.hu>, Pekka Enberg <penberg@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	torvalds@...ux-foundation.org, akpm@...ux-foundation.org,
	tj@...nel.org, npiggin@...nel.dk, rientjes@...gle.com,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH] slub: Disable the lockless allocator

Indeed I can reproduce it easily.
With a few printk's this shows that alloc_percpu() returns a wrong
address which is the cause of all of this:

logs:

Memory: 1011444k/1048564k available (11622k kernel code, 452k absent,
36668k reserved, 6270k data, 1028k init)
alloc_kmem_cache_cpus kmem_cache_node = ffff88003ffcf000
alloc_kmem_cache_cpus kmem_cache = ffff88003ffcf020

This means that the cpu_slab is not a percpu pointer.

Now the first allocation attempt:

Slab kmem_cache cpu_slab=ffff88003ffcf020 freelist=ffff88003f8020c0
BUG: unable to handle kernel paging request at ffff87ffc1fdc020
IP: [<ffffffff812c3852>] this_cpu_cmpxchg16b_emu+0x2/0x1c

Tejun: Whats going on there? I should be getting offsets into the per cpu
area and not kernel addresses.

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