linux-kernel - Re: [0/2 -tip] microcode: bug-fix + updates

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Message-Id: <1219217486.10800.398.camel@twins>
Date:	Wed, 20 Aug 2008 09:31:26 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Dmitry Adamushko <dmitry.adamushko@...il.com>
Cc:	Ingo Molnar <mingo@...e.hu>, Peter Oruba <peter.oruba@....com>,
	Tigran Aivazian <tigran@...azian.fsnet.co.uk>,
	Max Krasnyansky <maxk@...lcomm.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [0/2 -tip] microcode: bug-fix + updates

On Wed, 2008-08-20 at 00:10 +0200, Dmitry Adamushko wrote:
> [ Peter Z., you may jump immediately to [*] :-) ]

Thanks - does the below help?

> [*] btw., with DEBUG being enabled, pr_debug() generates [1] when 
> debug_smp_processor_id() is used (CONFIG_DEBUG_PREEMPT).
> 
> the problem seems to be caused by the following commit:
> commit b845b517b5e3706a3729f6ea83b88ab85f0725b0
> Author: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> Date:   Fri Aug 8 21:47:09 2008 +0200
> 
>     printk: robustify printk
> 
> 
> wake_up_klogd() -> __get_cpu_var() -> smp_processor_id()
> 
> and that's being called from release_console_sem() which is, in turn,
> said to be "may be called from any context" [2]
> 
> and in this case, it seems to be called from some non-preemptible
> context (although, it can't be printk()...
> although, I haven't looked carefully yet).
> 
> Provided [2], __get_cpu_var() is perhaps not the right solution there.
> 
> 
> [1]
> 
> [ 7697.942005] BUG: using smp_processor_id() in preemptible [00000000] code: syslogd/3542
> [ 7697.942005] caller is wake_up_klogd+0x1b/0x50
> [ 7697.942005] Pid: 3542, comm: syslogd Not tainted 2.6.27-rc3-tip-git #2
> [ 7697.942005] Call Trace:
> [ 7697.942005]  [<ffffffff8036b398>] debug_smp_processor_id+0xe8/0xf0
> [ 7697.942005]  [<ffffffff80239d3b>] wake_up_klogd+0x1b/0x50
> [ 7697.942005]  [<ffffffff8023a047>] release_console_sem+0x1e7/0x200
> [ 7697.942005]  [<ffffffff803c0f17>] do_con_write+0xb7/0x1f30
> [ 7697.942005]  [<ffffffff8020d920>] ? show_trace+0x10/0x20
> [ 7697.942005]  [<ffffffff8020dc42>] ? dump_stack+0x72/0x80
> [ 7697.942005]  [<ffffffff8036392d>] ? __ratelimit+0xbd/0xe0
> [ 7697.942005]  [<ffffffff8036b398>] ? debug_smp_processor_id+0xe8/0xf0
> [ 7697.942005]  [<ffffffff80239d3b>] ? wake_up_klogd+0x1b/0x50
> [ 7697.942005]  [<ffffffff8023a047>] ? release_console_sem+0x1e7/0x200
> [ 7697.942005]  [<ffffffff803c2de9>] con_write+0x19/0x30
> [ 7697.942005]  [<ffffffff803b37b6>] write_chan+0x276/0x3c0
> [ 7697.942005]  [<ffffffff80232b20>] ? default_wake_function+0x0/0x10
> [ 7697.942005]  [<ffffffff804cb872>] ? _spin_lock_irqsave+0x22/0x50
> [ 7697.942005]  [<ffffffff803b1334>] tty_write+0x194/0x260
> [ 7697.942005]  [<ffffffff803b3540>] ? write_chan+0x0/0x3c0
> [ 7697.942005]  [<ffffffff803b14a4>] redirected_tty_write+0xa4/0xb0
> [ 7697.942005]  [<ffffffff803b1400>] ? redirected_tty_write+0x0/0xb0
> [ 7697.942005]  [<ffffffff802a88c2>] do_loop_readv_writev+0x52/0x80
> [ 7697.942005]  [<ffffffff802a939d>] do_readv_writev+0x1bd/0x1d0
> [ 7697.942005]  [<ffffffff802a93e9>] vfs_writev+0x39/0x60
> [ 7697.942005]  [<ffffffff802a9870>] sys_writev+0x50/0x90
> [ 7697.942005]  [<ffffffff8020bb3b>] system_call_fastpath+0x16/0x1b


---
diff --git a/kernel/printk.c b/kernel/printk.c
index 655cc2c..57e9cd7 100644
--- a/kernel/printk.c
+++ b/kernel/printk.c
@@ -1000,7 +1000,7 @@ int printk_needs_cpu(int cpu)
 void wake_up_klogd(void)
 {
 	if (waitqueue_active(&log_wait))
-		__get_cpu_var(printk_pending) = 1;
+		__raw_get_cpu_var(printk_pending) = 1;
 }
 
 /**


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