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Date: Thu, 20 May 2004 00:21:31 -0700
From: Andrew Morton <akpm@osdl.org>
To: Ricky Beam <jfbeam@bluetronic.net>
Cc: linux-kernel@vger.kernel.org
Subject: Re: overlaping printk
Message-Id: <20040520002131.0afeceb9.akpm@osdl.org>
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Ricky Beam <jfbeam@bluetronic.net> wrote:
>
> Can anyone explain why the kernel does this on a serial console:
> 
>  C<PU0 >C2P:U M 3a:ch Mianech iCnhee cCk heExckc epEtxcieopnt: i0o0n0: 0000000000
>  0000000000000040

<looks>

<after three years, penny finally drops>

We bust the spinlock for *every* printk call.  No wonder.


diff -puN kernel/printk.c~printk-mangling-fix kernel/printk.c
--- 25/kernel/printk.c~printk-mangling-fix	2004-05-20 00:20:06.388725128 -0700
+++ 25-akpm/kernel/printk.c	2004-05-20 00:20:27.228556992 -0700
@@ -492,8 +492,10 @@ asmlinkage int printk(const char *fmt, .
 	char *p;
 	static char printk_buf[1024];
 	static int log_level_unknown = 1;
+	static int once;
 
-	if (oops_in_progress) {
+	if (oops_in_progress && !once) {
+		once = 1;
 		/* If a crash is occurring, make sure we can't deadlock */
 		spin_lock_init(&logbuf_lock);
 		/* And make sure that we print immediately */

_