linux-kernel - Re: BUG: unable to handle kernel paging request at ffffffffffffffff

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Date:	Wed, 18 Aug 2010 12:06:30 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Cc:	Ingo Molnar <mingo@...e.hu>, "H. Peter Anvin" <hpa@...or.com>,
	linux-kernel@...r.kernel.org
Subject: Re: BUG: unable to handle kernel paging request at ffffffffffffffff

On Fri, 13 Aug 2010 16:49:47 +0300
Sergey Senozhatsky <sergey.senozhatsky@...il.com> wrote:

> Hello,
> 
> yet another trace:
> 
> [ 5845.374558] CPU 1 is now offline
> [ 5845.376169] INFO: trying to register non-static key.
> [ 5845.376251] the code is fine but needs lockdep annotation.
> [ 5845.376327] turning off the locking correctness validator.
> [ 5845.376405] Pid: 6754, comm: bash Not tainted 2.6.36-rc0-git12-07921-g60bf26a-dirty #122
> [ 5845.376521] Call Trace:
> [ 5845.376570]  [<ffffffff81063e89>] __lock_acquire+0x2d1/0x17fd
> [ 5845.376657]  [<ffffffff81132b2a>] ? sysfs_deactivate+0x3e/0xec
> [ 5845.376747]  [<ffffffff81062ddd>] ? mark_held_locks+0x50/0x72
> [ 5845.376834]  [<ffffffff81065893>] lock_acquire+0x97/0xb6
> [ 5845.376917]  [<ffffffff8137145b>] ? percpu_counter_hotcpu_callback+0x3e/0x93
> [ 5845.377021]  [<ffffffff81374321>] ? mutex_lock_nested+0x2f3/0x31b
> [ 5845.377113]  [<ffffffff81371446>] ? percpu_counter_hotcpu_callback+0x29/0x93
> [ 5845.377218]  [<ffffffff8137568d>] _raw_spin_lock_irqsave+0x4e/0x60
> [ 5845.377312]  [<ffffffff8137145b>] ? percpu_counter_hotcpu_callback+0x3e/0x93
> [ 5845.377409]  [<ffffffff8137145b>] percpu_counter_hotcpu_callback+0x3e/0x93
> [ 5845.377475]  [<ffffffff81057344>] notifier_call_chain+0x32/0x5e
> [ 5845.377529]  [<ffffffff8105738f>] __raw_notifier_call_chain+0x9/0xb
> [ 5845.377587]  [<ffffffff8103c6e3>] __cpu_notify+0x1b/0x2d
> [ 5845.377638]  [<ffffffff8103c703>] cpu_notify+0xe/0x10
> [ 5845.377684]  [<ffffffff8103c70e>] cpu_notify_nofail+0x9/0x11
> [ 5845.377738]  [<ffffffff81362d82>] _cpu_down+0x151/0x206
> [ 5845.377786]  [<ffffffff81362ea8>] cpu_down+0x28/0x35
> [ 5845.377833]  [<ffffffff8136430d>] store_online+0x27/0x6e
> [ 5845.377884]  [<ffffffff812923ab>] sysdev_store+0x1b/0x1d
> [ 5845.377933]  [<ffffffff811321b2>] sysfs_write_file+0x103/0x13f
> [ 5845.377990]  [<ffffffff810daf92>] vfs_write+0xb0/0x14f
> [ 5845.378038]  [<ffffffff810db22e>] sys_write+0x45/0x6c
> [ 5845.378088]  [<ffffffff81002002>] system_call_fastpath+0x16/0x1b
> [ 5845.378166] BUG: unable to handle kernel paging request at ffffffffffffffff
> [ 5845.378236] IP: [<ffffffff81371487>] percpu_counter_hotcpu_callback+0x6a/0x93

It appears that one of the counters on the global list has been
trashed: lockdep doesn't recognise its spinlock and its internal
pointers are all-ones.

We need to identify that counter and then go take a look at whichever
subsystem ownes it.

A crude approach is:

--- a/lib/percpu_counter.c~a
+++ a/lib/percpu_counter.c
@@ -69,6 +69,8 @@ EXPORT_SYMBOL(__percpu_counter_sum);
 int __percpu_counter_init(struct percpu_counter *fbc, s64 amount,
 			  struct lock_class_key *key)
 {
+	printk("__percpu_counter_init(%p)\n", fbc);
+	dump_stack();
 	spin_lock_init(&fbc->lock);
 	lockdep_set_class(&fbc->lock, key);
 	fbc->count = amount;
@@ -126,6 +128,7 @@ static int __cpuinit percpu_counter_hotc
 		s32 *pcount;
 		unsigned long flags;
 
+		printk("percpu_counter_hotcpu_callback(%p)\n", fbc);
 		spin_lock_irqsave(&fbc->lock, flags);
 		pcount = per_cpu_ptr(fbc->counters, cpu);
 		fbc->count += *pcount;
_

If you can please apply that patch and then make it crash?  We can use
the address from the percpu_counter_hotcpu_callback() printk to look up
the stack trace from __percpu_counter_init() which will lead us to the
code which owns that counter.

Thanks.
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