linux-kernel - Re: NULL dereference OOPS on SysRq-w

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Message-ID: <a8e1da0804280008s38d3b16vfedb3860cd7d5222@mail.gmail.com>
Date:	Mon, 28 Apr 2008 15:08:36 +0800
From:	"Dave Young" <hidave.darkstar@...il.com>
To:	dpn@...merica.net
Cc:	"Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>,
	mingo@...e.hu
Subject: Re: NULL dereference OOPS on SysRq-w

On Mon, Apr 28, 2008 at 3:01 PM, Dan Noe <dpn@...merica.net> wrote:
> Dave Young wrote:
>
> > [snip]
> >
> > I have a fix for the NULL pointer reference BUG, tested on my pc.
> > ---
> >
> > "m" will be NULL if seq_printf & seq_puts is called from sched_debug_show
> > Use SEQ_* macros to fix it
> > Signed-off-by: Dave Young <hidave.darkstar@...il.com>
> >
>
>  There is actually already a patch out for this which simply hasn't made it
> upstream yet - Mike Galbraith emailed me with it and it indeed fixes the
> problem.  I hadn't realized his email didn't go to lkml.. otherwise I would
> have echoed that here to avoid wasting people's time.  My apologies.

Ok, thanks.

While debuging this issue I found another BUG about sysrq,

echo w >/proc/sys/kernel/sysrq
My system hangs, there's no response from then on.

>
>  Cheers,
>  Dan
>
>  ===
>
>  Here is his message:
>
>  From: efault@....de
>
>  Peter's fix didn't make it up-stream.
>
>  Subject: sched: fix oops
>
>  sched_debug uses SEQ_printf to use printk when the seqfile 'm' is NULL.
>  Instead of doing that here too; choose to not output the weight tree
>  to cut back on output.
>
>  Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
>  ---
>  diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
>  index 89fa32b..353a481 100644
>  --- a/kernel/sched_fair.c
>  +++ b/kernel/sched_fair.c
>  @@ -1643,8 +1643,10 @@ static void print_cfs_stats(struct seq_file *m, int
> cpu)
>
>         for_each_leaf_cfs_rq(cpu_rq(cpu), cfs_rq)
>                 print_cfs_rq(m, cpu, cfs_rq);
>
>  -       seq_printf(m, "\nWeight tree:\n");
>  -       print_cfs_rq_tasks(m, &cpu_rq(cpu)->cfs, 1);
>  +       if (m) {
>  +               seq_printf(m, "\nWeight tree:\n");
>
>  +               print_cfs_rq_tasks(m, &cpu_rq(cpu)->cfs, 1);
>  +       }
>         rcu_read_unlock();
>   }
>   #endif
>
>
>
>
>  --
>                     /--------------- - -  -  -   -   -
>                     |  Dan Noe
>                     |  http://isomerica.net/~dpn/
>
--
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