linux-kernel - Re: [PATCH v2] preempt: fix kernel build with !CONFIG

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Date:	Thu, 28 Oct 2010 22:47:03 +0300
From:	"Kirill A. Shutemov" <kirill@...temov.name>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	linux-kernel@...r.kernel.org, Avi Kivity <avi@...hat.com>,
	Brian Gerst <brgerst@...il.com>,
	David Howells <dhowells@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Pekka Enberg <penberg@...nel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Suresh Siddha <suresh.b.siddha@...el.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Venkatesh Pallipadi <venki@...gle.com>, x86@...nel.org
Subject: Re: [PATCH v2] preempt: fix kernel build with !CONFIG_BKL

On Thu, Oct 28, 2010 at 04:12:33PM +0200, Arnd Bergmann wrote:
> The preempt count logic tries to take the BKL into account, which breaks
> when CONFIG_BKL is not set.
> 
> Use the same preempt_count offset that we use without CONFIG_PREEMPT
> when CONFIG_BKL is disabled.
> 
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> Reported-by: Kirill Shutemov <kirill@...temov.name>
> ---
> > On Thursday 28 October 2010, Kirill A. Shutemov wrote:
> > On Thu, Oct 28, 2010 at 01:20:44PM +0200, Arnd Bergmann wrote:
> > > The preempt count logic tries to take the BKL into account, which breaks
> > > when CONFIG_BKL is not set.
> > > 
> > > Use the same preempt_count offset that we use without CONFIG_PREEMPT
> > > when CONFIG_BKL is disabled.
> > > 
> > > Signed-off-by: Arnd Bergmann <arnd@...db.de>
> > > Reported-by: "Kirill A. Shutemov" <kirill@...temov.name>
> > 
> > Remove quotes, please.
> 
> That would make it an invalid email address because of the dot. I left out
> the middle initial now, if that's better.

Hm... You are right. But this wasn't a problem before (see git log).
Let's leave it with quotes.

> 
> > I've got a lot of __schedule_bug. Log attached.
> 
> Ok. I really don't understand the preempt code all that well, let's
> hope that this one is right.
> 
> Thanks for your patience and for your testing!

It's usable now.

I'm not sure if it connected or not:

[ 6001.589151] INFO: task awesome:26743 blocked for more than 120 seconds.
[ 6001.589159] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
[ 6001.589166] awesome       D 00000555  7040 26743   3789 0x00000000
[ 6001.589182]  f19afe3c 00000046 5e569d25 00000555 c16ac7c0 f1ae0d40 c16ac7c0 c16ac7c0
[ 6001.589206]  f1ae0fc0 00000000 c16ac7c0 00000000 00000555 f1ae0d40 f4d46dc0 f19aff00
[ 6001.589228]  7fffffff f1ae0d40 f19afe9c c1317ea5 00000002 00000001 00000000 c131c57b
[ 6001.589251] Call Trace:
[ 6001.589271]  [<c1317ea5>] schedule_timeout+0x27/0xb8
[ 6001.589284]  [<c131c57b>] ? sub_preempt_count+0x9/0x8e
[ 6001.589298]  [<c105290d>] ? get_parent_ip+0xb/0x31
[ 6001.589307]  [<c131c5f3>] ? sub_preempt_count+0x81/0x8e
[ 6001.589318]  [<c13174d2>] wait_for_common+0xa0/0xef
[ 6001.589329]  [<c1057c3c>] ? default_wake_function+0x0/0x12
[ 6001.589339]  [<c13175c0>] wait_for_completion+0x17/0x19
[ 6001.589352]  [<c109a136>] stop_one_cpu+0x59/0x7f
[ 6001.589361]  [<c10579e6>] ? migration_cpu_stop+0x0/0x2d
[ 6001.589373]  [<c1317463>] ? wait_for_common+0x31/0xef
[ 6001.589384]  [<c1052e69>] sched_exec+0xa7/0xbb
[ 6001.589395]  [<c1101e09>] do_execve+0xb7/0x24a
[ 6001.589407]  [<c1030b84>] sys_execve+0x31/0x54
[ 6001.589418]  [<c102b3ba>] ptregs_execve+0x12/0x18
[ 6001.589429]  [<c1319d00>] ? syscall_call+0x7/0xb
[ 6001.589438] 1 lock held by awesome/26743:
[ 6001.589444]  #0:  (&sig->cred_guard_mutex){......}, at: [<c1100d1e>] prepare_bprm_creds+0x25/0x5a

I probably saw it previously on pre-2.6.37-rc1 with CONFIG_BKL=y.

> 
> 	Arnd
> 
> diff --git a/include/linux/hardirq.h b/include/linux/hardirq.h
> index 8a389b6..41cb31f 100644
> --- a/include/linux/hardirq.h
> +++ b/include/linux/hardirq.h
> @@ -96,11 +96,15 @@
>   */
>  #define in_nmi()	(preempt_count() & NMI_MASK)
>  
> -#if defined(CONFIG_PREEMPT)
> +#if defined(CONFIG_PREEMPT) && defined(CONFIG_BKL)
>  # define PREEMPT_INATOMIC_BASE kernel_locked()
> -# define PREEMPT_CHECK_OFFSET 1
>  #else
>  # define PREEMPT_INATOMIC_BASE 0
> +#endif
> +
> +#if defined(CONFIG_PREEMPT)
> +# define PREEMPT_CHECK_OFFSET 1
> +#else
>  # define PREEMPT_CHECK_OFFSET 0
>  #endif
>  

-- 
 Kirill A. Shutemov
--
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