linux-kernel - Re: kmemleak for MIPS

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Date:	Wed, 30 Mar 2011 15:07:48 +0100
From:	Catalin Marinas <catalin.marinas@....com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Maxin John <maxin.john@...il.com>,
	Daniel Baluta <daniel.baluta@...il.com>,
	naveen yadav <yad.naveen@...il.com>, linux-mips@...ux-mips.org,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: kmemleak for MIPS

On Wed, 2011-03-30 at 14:27 +0100, Eric Dumazet wrote:
> Le mercredi 30 mars 2011 à 14:17 +0100, Maxin John a écrit :
> > I have compiled the kernel with below given modification in .config
> >
> > CONFIG_CMDLINE="uhash_entries=256"
> >
> > After booting with the new kernel, the "kmemleak" no longer complains
> > about the "udp_table_init".
> > However it do report another possible leak :)
> >
> > debian-mips:~# cat /sys/kernel/debug/kmemleak
> > unreferenced object 0x8f085000 (size 4096):
> >   comm "swapper", pid 1, jiffies 4294937670 (age 1043.280s)
> >   hex dump (first 32 bytes):
> >     00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
> >     00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
> >   backtrace:
> >     [<801ac7a8>] __kmalloc+0x130/0x180
> >     [<80532500>] flow_cache_cpu_prepare+0x50/0xa8
> >     [<8052378c>] flow_cache_init_global+0x90/0x138
> >     [<80100584>] do_one_initcall+0x174/0x1e0
> >     [<8050c348>] kernel_init+0xe4/0x174
> >     [<80103d4c>] kernel_thread_helper+0x10/0x18
> > debian-mips:~#
> 
> Hmm, then MIPS kmemleak port might have a problem with percpu data ?
> 
> fcp->hash_table = kzalloc_node(sz, GFP_KERNEL, cpu_to_node(cpu));
> 
> fcp is a per cpu "struct flow_cache_percpu"

I can't figure out what it is. Kmemleak uses this block for scanning the
percpu data:

	for_each_possible_cpu(i)
		scan_block(__per_cpu_start + per_cpu_offset(i),
			   __per_cpu_end + per_cpu_offset(i), NULL, 1);

The __per_cpu_* symbols seem to be correctly defined in the MIPS
vmlinux.lds.S as it uses the PERCPU macro directly.

Other chunks allocated via pcpu_mem_alloc() should be tracked by
kmemleak and either reported as leaks or scanned (and not reporting
subsequent blocks referred from the percpu memory).

-- 
Catalin


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