linux-kernel - Re: per-cpu related?

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Date:	Sun, 13 Jul 2008 13:55:22 +0200
From:	"Vegard Nossum" <vegard.nossum@...il.com>
To:	"Yinghai Lu" <yhlu.kernel@...il.com>
Cc:	"Ingo Molnar" <mingo@...e.hu>, LKML <linux-kernel@...r.kernel.org>,
	"Mike Travis" <travis@....com>,
	"Thomas Gleixner" <tglx@...utronix.de>,
	"Steven Rostedt" <rostedt@...dmis.org>
Subject: Re: per-cpu related?

Hi,

On Sun, Jul 13, 2008 at 10:16 AM, Yinghai Lu <yhlu.kernel@...il.com> wrote:
> calling  pcie_portdrv_init+0x0/0x77
> BUG: unable to handle kernel NULL pointer dereference at 0000000000000000
> IP: [<ffffffff802557de>] hrtick_start_fair+0x8e/0x178
> PGD 0
> Oops: 0000 [1] SMP
> CPU 4
> Modules linked in:
> Pid: 103, comm: events/4 Not tainted 2.6.26-rc9-tip-01834-g99e624f-dirty #354
> RIP: 0010:[<ffffffff802557de>]  [<ffffffff802557de>]
> hrtick_start_fair+0x8e/0x178

I find that this corresponds to timer->base being NULL:

static inline int hrtimer_is_hres_active(struct hrtimer *timer)
{
        return timer->base->cpu_base->hres_active;
}

Apparently timer->base can legitimately be NULL in some cases:

/*
 * [...]
 * When the timer's base is locked, and the timer removed from list, it is
 * possible to set timer->base = NULL and drop the lock: the timer remains
 * locked.
 */

I don't know any more than this yet, I hope I didn't waste your time.


Vegard

-- 
"The animistic metaphor of the bug that maliciously sneaked in while
the programmer was not looking is intellectually dishonest as it
disguises that the error is the programmer's own creation."
	-- E. W. Dijkstra, EWD1036
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