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Subject[PATCH] disentangle printk's whilst oopsing on SMP
Date

Hi Linus,

The attached patch stops printk's issued on different processors from becoming
char-by-char interleaved whilst one of them is oopsing.

David

diff -uNr linux-2.5.72/kernel/printk.c linux-2.5.72-auto/kernel/printk.c
--- linux-2.5.72/kernel/printk.c 2003-06-17 15:01:58.000000000 +0100
+++ linux-2.5.72-auto/kernel/printk.c 2003-06-17 15:06:31.000000000 +0100
@@ -373,6 +373,9 @@
logged_chars++;
}

+/* cpu currently holding logbuf_lock */
+static volatile int printk_cpu = -1;
+
/*
* This is printk. It can be called from any context. We want it to work.
*
@@ -395,8 +398,9 @@
static char printk_buf[1024];
static int log_level_unknown = 1;

- if (oops_in_progress) {
- /* If a crash is occurring, make sure we can't deadlock */
+ if (oops_in_progress && printk_cpu==smp_processor_id()) {
+ /* If a crash is occurring during printk() on this CPU,
+ * make sure we can't deadlock */
spin_lock_init(&logbuf_lock);
/* And make sure that we print immediately */
init_MUTEX(&console_sem);
@@ -404,6 +408,7 @@

/* This stops the holder of console_sem just where we want him */
spin_lock_irqsave(&logbuf_lock, flags);
+ printk_cpu = smp_processor_id();

/* Emit the output into the temporary buffer */
va_start(args, fmt);
-
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