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To: linux-kernel@vger.kernel.org
Cc: j-nomura@ce.jp.nec.com
Subject: [PATCH] 2.4.16 kernel/printk.c (per processor initialization check)
From: j-nomura@ce.jp.nec.com
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Message-Id: <20011203144615C.nomura@hpc.bs1.fc.nec.co.jp>
Date: Mon, 03 Dec 2001 14:46:15 +0900
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Hello,

I experienced system hang on my SMP machine and it turned out to be due to
console write before mmu initialization completes.

To be more specific, even if secondary processors are not in status enough
to do actual console I/O (e.g. mmu is not initialized), call_console_drivers()
tries to do it.
This leads to unpredictable result. For me, for example, it cause machine
check abort and hang up system.

Attached is a patch for it.

--- kernel/printk.c	2001/11/27 04:41:49	1.1.1.8
+++ kernel/printk.c	2001/12/03 05:25:26
@@ -491,20 +491,22 @@
  */
 void release_console_sem(void)
 {
 	unsigned long flags;
 	unsigned long _con_start, _log_end;
 	unsigned long must_wake_klogd = 0;
 
 	for ( ; ; ) {
 		spin_lock_irqsave(&logbuf_lock, flags);
 		must_wake_klogd |= log_start - log_end;
+		if (!(cpu_online_map & 1UL << smp_processor_id()))
+			break;
 		if (con_start == log_end)
 			break;			/* Nothing to print */
 		_con_start = con_start;
 		_log_end = log_end;
 		con_start = log_end;		/* Flush */
 		spin_unlock_irqrestore(&logbuf_lock, flags);
 		call_console_drivers(_con_start, _log_end);
 	}
 	console_may_schedule = 0;
 	up(&console_sem);

Best regards.
--
NOMURA, Jun'ichi <j-nomura@ce.jp.nec.com, nomura@hpc.bs1.fc.nec.co.jp>
HPC Operating System Group, 1st Computers Software Division,
Computers Software Operations Unit, NEC Solutions.
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