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@@ -20,10 +20,13 @@
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#include <linux/nmi.h>
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#include <linux/kexec.h>
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-int panic_timeout;
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int panic_on_oops;
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int tainted;
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+static int pause_on_oops;
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+static int pause_on_oops_flag;
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+static DEFINE_SPINLOCK(pause_on_oops_lock);
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+int panic_timeout;
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EXPORT_SYMBOL(panic_timeout);
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struct notifier_block *panic_notifier_list;
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@@ -174,3 +177,95 @@ void add_taint(unsigned flag)
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tainted |= flag;
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}
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EXPORT_SYMBOL(add_taint);
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+
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+static int __init pause_on_oops_setup(char *str)
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+{
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+ pause_on_oops = simple_strtoul(str, NULL, 0);
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+ return 1;
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+}
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+__setup("pause_on_oops=", pause_on_oops_setup);
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+
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+static void spin_msec(int msecs)
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+{
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+ int i;
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+
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+ for (i = 0; i < msecs; i++) {
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+ touch_nmi_watchdog();
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+ mdelay(1);
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+ }
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+}
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+
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+/*
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+ * It just happens that oops_enter() and oops_exit() are identically
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+ * implemented...
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+ */
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+static void do_oops_enter_exit(void)
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+{
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+ unsigned long flags;
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+ static int spin_counter;
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+
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+ if (!pause_on_oops)
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+ return;
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+
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+ spin_lock_irqsave(&pause_on_oops_lock, flags);
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+ if (pause_on_oops_flag == 0) {
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+ /* This CPU may now print the oops message */
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+ pause_on_oops_flag = 1;
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+ } else {
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+ /* We need to stall this CPU */
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+ if (!spin_counter) {
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+ /* This CPU gets to do the counting */
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+ spin_counter = pause_on_oops;
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+ do {
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+ spin_unlock(&pause_on_oops_lock);
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+ spin_msec(MSEC_PER_SEC);
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+ spin_lock(&pause_on_oops_lock);
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+ } while (--spin_counter);
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+ pause_on_oops_flag = 0;
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+ } else {
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+ /* This CPU waits for a different one */
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+ while (spin_counter) {
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+ spin_unlock(&pause_on_oops_lock);
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+ spin_msec(1);
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+ spin_lock(&pause_on_oops_lock);
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+ }
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+ }
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+ }
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+ spin_unlock_irqrestore(&pause_on_oops_lock, flags);
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+}
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+
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+/*
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+ * Return true if the calling CPU is allowed to print oops-related info. This
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+ * is a bit racy..
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+ */
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+int oops_may_print(void)
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+{
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+ return pause_on_oops_flag == 0;
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+}
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+
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+/*
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+ * Called when the architecture enters its oops handler, before it prints
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+ * anything. If this is the first CPU to oops, and it's oopsing the first time
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+ * then let it proceed.
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+ *
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+ * This is all enabled by the pause_on_oops kernel boot option. We do all this
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+ * to ensure that oopses don't scroll off the screen. It has the side-effect
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+ * of preventing later-oopsing CPUs from mucking up the display, too.
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+ *
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+ * It turns out that the CPU which is allowed to print ends up pausing for the
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+ * right duration, whereas all the other CPUs pause for twice as long: once in
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+ * oops_enter(), once in oops_exit().
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+ */
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+void oops_enter(void)
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+{
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+ do_oops_enter_exit();
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+}
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+
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+/*
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+ * Called when the architecture exits its oops handler, after printing
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+ * everything.
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+ */
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+void oops_exit(void)
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+{
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+ do_oops_enter_exit();
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+}
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Andrew Morton