Add an escape hatch for "NMI-safer" printing
When debugging, I often want print a backtrace in NMI context. That's
not particularly safe, and for the watchdog, hanging the machine is a
bad idea.
These dirty bools will let us skip the two locks *that I know about*
from the printing code paths. Super brittle.
Signed-off-by: Barret Rhoden <brho@cs.berkeley.edu>
diff --git a/kern/arch/x86/console.c b/kern/arch/x86/console.c
index 9c4bd5c..89099bf 100644
--- a/kern/arch/x86/console.c
+++ b/kern/arch/x86/console.c
@@ -252,6 +252,7 @@
#define SCROLLING_CRT_SIZE (MAX_SCROLL_LENGTH * CRT_SIZE)
static spinlock_t console_lock = SPINLOCK_INITIALIZER_IRQSAVE;
+bool panic_skip_console_lock;
static unsigned addr_6845;
static uint16_t *crt_buf;
@@ -655,7 +656,8 @@
{
void logbuf(int c);
- spin_lock_irqsave(&console_lock);
+ if (!panic_skip_console_lock)
+ spin_lock_irqsave(&console_lock);
#ifndef CONFIG_SERIAL_IO
serial_spam_char(c);
@@ -664,7 +666,8 @@
cga_putc(c);
logbuf(c);
- spin_unlock_irqsave(&console_lock);
+ if (!panic_skip_console_lock)
+ spin_unlock_irqsave(&console_lock);
}
// `High'-level console I/O. Used by readline and cprintf.
diff --git a/kern/arch/x86/console.h b/kern/arch/x86/console.h
index e2660f8..6cc5737 100644
--- a/kern/arch/x86/console.h
+++ b/kern/arch/x86/console.h
@@ -26,6 +26,9 @@
SLIST_HEAD(cons_dev_slist, cons_dev);
extern struct cons_dev_slist cdev_list;
+/* Set this to turn off console locking. (debugging/panic/NMI) */
+extern bool panic_skip_console_lock;
+
void cons_init(void);
/* Returns 0 on success, with the char in *data */
int cons_get_char(struct cons_dev *cdev, uint8_t *data);
diff --git a/kern/include/stdio.h b/kern/include/stdio.h
index fd9cbaf..fc89b39 100644
--- a/kern/include/stdio.h
+++ b/kern/include/stdio.h
@@ -35,6 +35,7 @@
void vprintfmt(void (*putch)(int, void**), void **putdat, const char *fmt, va_list);
// lib/printf.c
+extern bool panic_skip_print_lock;
void print_lock(void);
void print_unlock(void);
void print_unlock_force(void);
diff --git a/kern/src/printf.c b/kern/src/printf.c
index 7b415d9..3fd7ddb 100644
--- a/kern/src/printf.c
+++ b/kern/src/printf.c
@@ -15,9 +15,13 @@
static spinlock_t output_lock = SPINLOCK_INITIALIZER_IRQSAVE;
static int output_lock_holder = -1; /* core_id. */
static int output_lock_count;
+bool panic_skip_print_lock;
void print_lock(void)
{
+ if (panic_skip_print_lock)
+ return;
+
if (output_lock_holder == core_id_early()) {
output_lock_count++;
return;
@@ -30,6 +34,9 @@
void print_unlock(void)
{
+ if (panic_skip_print_lock)
+ return;
+
output_lock_count--;
if (output_lock_count)
return;
