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SubjectRe: [prepatch] removal of oops->printk deadlocks
Ingo Molnar wrote:
>
> > So... In this updated patch the console_silent() call remains
> > as you designed it, but the nmi_watchdog kernel boot parameter has
> > been overloaded so that
> >
> > nmi_watchdog=2
> >
> > will now cause _all_ NMI oops messages to be displayed on the console.
> >
> > Is this OK?
>
> this collides with the UP-IOAPIC path's use of nmi_watchdog == 2 ...
>
> i'd rather suggest a cleaner, "nmi_watchdog=2,verbose" (default: silent)
> type of boot parameter, it looks like the NMI watchdog needs more
> parameters.


OK, so the options are now:

nmi_watchdog=0
nmi_watchdog=1
nmi_watchdog=1,verbose


Third time lucky?



--- linux-2.4.0-test11-pre5/include/linux/kernel.h Sun Oct 15 01:27:46 2000
+++ linux-akpm/include/linux/kernel.h Wed Nov 15 23:25:48 2000
@@ -62,6 +62,7 @@

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-pre5/include/asm-i386/page.h Sat Nov 4 16:22:49 2000
+++ linux-akpm/include/asm-i386/page.h Wed Nov 15 23:27:32 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-pre5/kernel/printk.c Sat Nov 4 16:22:49 2000
+++ linux-akpm/kernel/printk.c Wed Nov 15 23:25:48 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
@@ -251,6 +252,9 @@
return do_syslog(type, buf, len);
}

+/*
+ * printk("") may be used to wake up klogd
+ */
asmlinkage int printk(const char *fmt, ...)
{
va_list args;
@@ -260,6 +264,8 @@
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 +314,8 @@
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-pre5/arch/i386/mm/fault.c Wed Nov 15 23:00:16 2000
+++ linux-akpm/arch/i386/mm/fault.c Thu Nov 16 00:14:37 2000
@@ -77,17 +77,37 @@
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)
+{
+ if (yes) {
+ oops_in_progress = 1;
+#ifdef CONFIG_SMP
+ global_irq_lock = 0; /* Many serial drivers do __global_cli() */
+#endif
+ } else {
+ 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...
+ */
+ printk("");
+ }
+}
+
+void do_BUG(const char *file, int line)
{
- spin_lock_init(&console_lock);
- spin_lock_init(&timerlist_lock);
+ bust_spinlocks(1);
+ printk("kernel BUG at %s:%d!\n", file, line);
}

asmlinkage void do_invalid_op(struct pt_regs *, unsigned long);
@@ -264,8 +284,7 @@
* 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 +302,7 @@
printk(KERN_ALERT "*pte = %08lx\n", page);
}
die("Oops", regs, error_code);
+ bust_spinlocks(0);
do_exit(SIGKILL);

/*
--- linux-2.4.0-test11-pre5/arch/i386/kernel/traps.c Wed Nov 15 23:00:16 2000
+++ linux-akpm/arch/i386/kernel/traps.c Wed Nov 15 23:49:00 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-pre5/arch/i386/kernel/i386_ksyms.c Wed Nov 15 23:00:16 2000
+++ linux-akpm/arch/i386/kernel/i386_ksyms.c Wed Nov 15 23:25:48 2000
@@ -157,3 +157,5 @@
#ifdef CONFIG_X86_PAE
EXPORT_SYMBOL(empty_zero_page);
#endif
+
+EXPORT_SYMBOL(do_BUG);
--- linux-2.4.0-test11-pre5/drivers/char/console.c Wed Nov 15 23:00:16 2000
+++ linux-akpm/drivers/char/console.c Wed Nov 15 23:25:48 2000
@@ -2135,6 +2135,7 @@
}
}
set_cursor(currcons);
+ poke_blanked_console();

quit:
clear_bit(0, &printing);
@@ -2661,7 +2662,7 @@
return;
}
console_timer.function = blank_screen;
- if (blankinterval) {
+ if (blankinterval && !oops_in_progress) {
mod_timer(&console_timer, jiffies + blankinterval);
}

@@ -2683,14 +2684,18 @@

void poke_blanked_console(void)
{
- del_timer(&console_timer); /* Can't use _sync here: called from tasklet */
- if (vt_cons[fg_console]->vc_mode == KD_GRAPHICS)
- return;
- if (console_blanked) {
- console_timer.function = unblank_screen_t;
- mod_timer(&console_timer, jiffies); /* Now */
- } else if (blankinterval) {
- mod_timer(&console_timer, jiffies + blankinterval);
+ if (oops_in_progress) {
+ unblank_screen(); /* Just do it */
+ } else {
+ del_timer(&console_timer); /* Can't use _sync here: called from tasklet */
+ if (vt_cons[fg_console]->vc_mode == KD_GRAPHICS)
+ return;
+ if (console_blanked) {
+ console_timer.function = unblank_screen_t;
+ mod_timer(&console_timer, jiffies); /* Now */
+ } else if (blankinterval) {
+ mod_timer(&console_timer, jiffies + blankinterval);
+ }
}
}

--- linux-2.4.0-test11-pre5/Documentation/nmi_watchdog.txt Thu Aug 24 21:07:14 2000
+++ linux-akpm/Documentation/nmi_watchdog.txt Wed Nov 15 23:25:48 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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