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Date: Sat, 18 Nov 2000 14:53:27 +1100
From: Andrew Morton <andrewm@uow.edu.au>
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To: Linus Torvalds <torvalds@transmeta.com>
CC: lkml <linux-kernel@vger.kernel.org>
Subject: IGNORE Previous! [patch] Removal of oops->printk deadlocks
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[ Sorry - the last one was bogus test11-pre4 stuff ]

Linus,

this patch removes the final things which can cause oopses and other
sad events to deadlock without providing diagnostics.

I've changed it a little since Ingo provided comments - the
poke_blanked_console() changes have been simplified.

- If four places: oops, die(), NMI-oops and BUG() we call
  bust_spinlocks(1) to set `oops_in_progress' to tell the printk and
  console systems that they should not acquire any locks.

- After the message has gone out we call bust_spinlocks(0) to turn
  off oops_in_progress and to do a 'printk(" \b");'.  This allows
  printk() to wake up klogd and allows the vgacon driver to turn the
  screen back on.

- The NMI oopser has been enhanced so you can optionally get the NMI
  oops traces for all the CPUs.  You boot your kernel with the option:

	nmi_watchdog=1,verbose

  This is for those fun situations where your machine wedges after an
  NMI oops.

- This is pretty specific to x86/vgacon, but everything is in place
  for other architectures.



--- linux-2.4.0-test11-pre7/include/linux/kernel.h	Sat Nov 18 13:55:32 2000
+++ linux-akpm/include/linux/kernel.h	Sat Nov 18 14:44:08 2000
@@ -66,6 +66,7 @@
 
 asmlinkage int printk(const char * fmt, ...)
 	__attribute__ ((format (printf, 1, 2)));
+extern int oops_in_progress;
 
 #if DEBUG
 #define pr_debug(fmt,arg...) \
--- linux-2.4.0-test11-pre7/include/asm-i386/page.h	Sat Nov  4 16:22:49 2000
+++ linux-akpm/include/asm-i386/page.h	Sat Nov 18 14:44:08 2000
@@ -88,8 +88,9 @@
  * Tell the user there is some problem. Beep too, so we can
  * see^H^H^Hhear bugs in early bootup as well!
  */
+extern void do_BUG(const char *file, int line);
 #define BUG() do { \
-	printk("kernel BUG at %s:%d!\n", __FILE__, __LINE__); \
+	do_BUG(__FILE__, __LINE__); \
 	__asm__ __volatile__(".byte 0x0f,0x0b"); \
 } while (0)
 
--- linux-2.4.0-test11-pre7/kernel/printk.c	Sat Nov  4 16:22:49 2000
+++ linux-akpm/kernel/printk.c	Sat Nov 18 14:44:08 2000
@@ -51,6 +51,7 @@
 static unsigned long logged_chars;
 struct console_cmdline console_cmdline[MAX_CMDLINECONSOLES];
 static int preferred_console = -1;
+int oops_in_progress;
 
 /*
  *	Setup a list of consoles. Called from init/main.c
@@ -260,6 +261,8 @@
 	static signed char msg_level = -1;
 	long flags;
 
+	if (oops_in_progress)
+		spin_lock_init(&console_lock);
 	spin_lock_irqsave(&console_lock, flags);
 	va_start(args, fmt);
 	i = vsprintf(buf + 3, fmt, args); /* hopefully i < sizeof(buf)-4 */
@@ -308,7 +311,8 @@
 			msg_level = -1;
 	}
 	spin_unlock_irqrestore(&console_lock, flags);
-	wake_up_interruptible(&log_wait);
+	if (!oops_in_progress)
+		wake_up_interruptible(&log_wait);
 	return i;
 }
 
--- linux-2.4.0-test11-pre7/arch/i386/mm/fault.c	Sat Nov 18 13:55:28 2000
+++ linux-akpm/arch/i386/mm/fault.c	Sat Nov 18 14:44:08 2000
@@ -24,6 +24,7 @@
 #include <asm/hardirq.h>
 
 extern void die(const char *,struct pt_regs *,long);
+extern int console_loglevel;
 
 /*
  * Ugly, ugly, but the goto's result in better assembly..
@@ -77,17 +78,40 @@
 	return 0;
 }
 
-extern spinlock_t console_lock, timerlist_lock;
+#ifdef CONFIG_SMP
+extern unsigned volatile int global_irq_lock;
+#endif
 
 /*
  * Unlock any spinlocks which will prevent us from getting the
- * message out (timerlist_lock is aquired through the
- * console unblank code)
+ * message out and tell the printk/console paths that an emergency
+ * message is coming through
  */
-void bust_spinlocks(void)
+void bust_spinlocks(int yes)
 {
-	spin_lock_init(&console_lock);
-	spin_lock_init(&timerlist_lock);
+	if (yes) {
+		oops_in_progress = 1;
+#ifdef CONFIG_SMP
+		global_irq_lock = 0;	/* Many serial drivers do __global_cli() */
+#endif
+	} else {
+		int loglevel_save = console_loglevel;
+		oops_in_progress = 0;
+		/*
+		 * OK, the message is on the console.  Now we call printk()
+		 * without oops_in_progress set so that printk will give klogd
+		 * a poke.  Hold onto your hats...
+		 */
+		console_loglevel = 15;		/* NMI oopser may have shut the console up */
+		printk(" \b");
+		console_loglevel = loglevel_save;
+	}
+}
+
+void do_BUG(const char *file, int line)
+{
+	bust_spinlocks(1);
+	printk("kernel BUG at %s:%d!\n", file, line);
 }
 
 asmlinkage void do_invalid_op(struct pt_regs *, unsigned long);
@@ -264,8 +288,7 @@
  * terminate things with extreme prejudice.
  */
 
-	bust_spinlocks();
-
+	bust_spinlocks(1);
 	if (address < PAGE_SIZE)
 		printk(KERN_ALERT "Unable to handle kernel NULL pointer dereference");
 	else
@@ -283,6 +306,7 @@
 		printk(KERN_ALERT "*pte = %08lx\n", page);
 	}
 	die("Oops", regs, error_code);
+	bust_spinlocks(0);
 	do_exit(SIGKILL);
 
 /*
--- linux-2.4.0-test11-pre7/arch/i386/kernel/traps.c	Sat Nov 18 13:55:28 2000
+++ linux-akpm/arch/i386/kernel/traps.c	Sat Nov 18 14:44:08 2000
@@ -63,7 +63,7 @@
 struct desc_struct idt_table[256] __attribute__((__section__(".data.idt"))) = { {0, 0}, };
 
 extern int console_loglevel;
-extern void bust_spinlocks(void);
+extern void bust_spinlocks(int yes);
 
 static inline void console_silent(void)
 {
@@ -209,9 +209,10 @@
 {
 	console_verbose();
 	spin_lock_irq(&die_lock);
+	bust_spinlocks(1);
 	printk("%s: %04lx\n", str, err & 0xffff);
 	show_registers(regs);
-
+	bust_spinlocks(0);
 	spin_unlock_irq(&die_lock);
 	do_exit(SIGSEGV);
 }
@@ -386,10 +387,14 @@
 #if CONFIG_X86_IO_APIC
 
 int nmi_watchdog = 1;
+static int nmi_watchdog_verbose;
 
 static int __init setup_nmi_watchdog(char *str)
 {
-        get_option(&str, &nmi_watchdog);
+ 	if (get_option(&str, &nmi_watchdog) == 2) {
+		if (strcmp(str, "verbose") == 0)
+			nmi_watchdog_verbose = 1;
+	}
         return 1;
 }
 
@@ -414,7 +419,7 @@
 	 *  here too!]
 	 */
 
-	static unsigned int last_irq_sums [NR_CPUS],
+	static unsigned int	last_irq_sums [NR_CPUS],
 				alert_counter [NR_CPUS];
 
 	/*
@@ -437,12 +442,15 @@
 			 * We are in trouble anyway, lets at least try
 			 * to get a message out.
 			 */
-			bust_spinlocks();
+			bust_spinlocks(1);
 			printk("NMI Watchdog detected LOCKUP on CPU%d, registers:\n", cpu);
 			show_registers(regs);
-			printk("console shuts up ...\n");
-			console_silent();
+			if (nmi_watchdog_verbose == 0) {
+				printk("Console shuts up. Run dmesg or boot with `nmi_watchdog=1,verbose' for more logs\n");
+				console_silent();
+			}
 			spin_unlock(&nmi_print_lock);
+			bust_spinlocks(0);
 			do_exit(SIGSEGV);
 		}
 	} else {
--- linux-2.4.0-test11-pre7/arch/i386/kernel/i386_ksyms.c	Sat Nov 18 13:55:28 2000
+++ linux-akpm/arch/i386/kernel/i386_ksyms.c	Sat Nov 18 14:44:08 2000
@@ -157,3 +157,5 @@
 #ifdef CONFIG_X86_PAE
 EXPORT_SYMBOL(empty_zero_page);
 #endif
+
+EXPORT_SYMBOL(do_BUG);
--- linux-2.4.0-test11-pre7/drivers/char/console.c	Sat Nov 18 13:55:28 2000
+++ linux-akpm/drivers/char/console.c	Sat Nov 18 14:44:08 2000
@@ -2135,7 +2135,8 @@
 		}
 	}
 	set_cursor(currcons);
-
+	if (!oops_in_progress)
+		poke_blanked_console();
 quit:
 	clear_bit(0, &printing);
 }
--- linux-2.4.0-test11-pre7/Documentation/nmi_watchdog.txt	Thu Aug 24 21:07:14 2000
+++ linux-akpm/Documentation/nmi_watchdog.txt	Sat Nov 18 14:44:08 2000
@@ -24,8 +24,21 @@
 cannot even accept NMI interrupts, or the crash has made the kernel
 unable to print messages.
 
-NOTE: currently the NMI-oopser is enabled unconditionally on x86 SMP
-boxes.
+The NMI-oopser defaults to `1' (enabled) on x86 SMP boxes.
+
+The NMI-oopser only displays the first oops message on the console. This
+is to prevent vital information from scrolling off the scren if more
+errors occur.  You can find additional information (such as NMI oops
+information from other CPUs) by looking in your system logs or with
+the `dmesg' command.  
+
+If your system is crashing hard and preventing you from running `dmesg' 
+you can tell the NMI oopser to display all NMI oops messages (not just
+the first one) by setting
+
+	nmi_watchdog=1,verbose
+
+on the kernel boot command line or in lilo.conf, as shown above.
 
 [ feel free to send bug reports, suggestions and patches to
   Ingo Molnar <mingo@redhat.com> or the Linux SMP mailing
-
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