#include <stdio.h>
#include "devices/serial.h"
#include "devices/vga.h"
+#include "threads/init.h"
#include "threads/interrupt.h"
#include "threads/synch.h"
static void vprintf_helper (char, void *);
-static void putchar_unlocked (uint8_t c);
+static void putchar_have_lock (uint8_t c);
/* The console lock.
Both the vga and serial layers do their own locking, so it's
from mixing their output, which looks confusing. */
static struct lock console_lock;
+/* True in ordinary circumstances: we want to use the console
+ lock to avoid mixing output between threads, as explained
+ above.
+
+ False in early boot before the point that locks are functional
+ or the console lock has been initialized, or after a kernel
+ panics. In the former case, taking the lock would cause an
+ assertion failure, which in turn would cause a panic, turning
+ it into the latter case. In the latter case, if it is a buggy
+ lock_acquire() implementation that caused the panic, we'll
+ likely just recurse. */
+static bool use_console_lock;
+
+/* It's possible, if you add enough debug output to Pintos, to
+ try to recursively grab console_lock from a single thread. As
+ a real example, I added a printf() call to palloc_free().
+ Here's a real backtrace that resulted:
+
+ lock_console()
+ vprintf()
+ printf() - palloc() tries to grab the lock again
+ palloc_free()
+ thread_schedule_tail() - another thread dying as we switch threads
+ schedule()
+ thread_yield()
+ intr_handler() - timer interrupt
+ intr_set_level()
+ serial_putc()
+ putchar_have_lock()
+ putbuf()
+ sys_write() - one process writing to the console
+ syscall_handler()
+ intr_handler()
+
+ This kind of thing is very difficult to debug, so we avoid the
+ problem by simulating a recursive lock with a depth
+ counter. */
+static int console_lock_depth;
+
+/* Number of characters written to console. */
+static int64_t write_cnt;
+
+/* Enable console locking. */
void
console_init (void)
{
- lock_init (&console_lock, "console");
+ lock_init (&console_lock);
+ use_console_lock = true;
+}
+
+/* Notifies the console that a kernel panic is underway,
+ which warns it to avoid trying to take the console lock from
+ now on. */
+void
+console_panic (void)
+{
+ use_console_lock = false;
+}
+
+/* Prints console statistics. */
+void
+console_print_stats (void)
+{
+ printf ("Console: %lld characters output\n", write_cnt);
+}
+
+/* Acquires the console lock. */
+static void
+acquire_console (void)
+{
+ if (!intr_context () && use_console_lock)
+ {
+ if (lock_held_by_current_thread (&console_lock))
+ console_lock_depth++;
+ else
+ lock_acquire (&console_lock);
+ }
+}
+
+/* Releases the console lock. */
+static void
+release_console (void)
+{
+ if (!intr_context () && use_console_lock)
+ {
+ if (console_lock_depth > 0)
+ console_lock_depth--;
+ else
+ lock_release (&console_lock);
+ }
+}
+
+/* Returns true if the current thread has the console lock,
+ false otherwise. */
+static bool
+console_locked_by_current_thread (void)
+{
+ return (intr_context ()
+ || !use_console_lock
+ || lock_held_by_current_thread (&console_lock));
}
/* The standard vprintf() function,
{
int char_cnt = 0;
- if (!intr_context ())
- lock_acquire (&console_lock);
-
+ acquire_console ();
__vprintf (format, args, vprintf_helper, &char_cnt);
-
- if (!intr_context ())
- lock_release (&console_lock);
+ release_console ();
return char_cnt;
}
int
puts (const char *s)
{
- if (!intr_context ())
- lock_acquire (&console_lock);
-
+ acquire_console ();
while (*s != '\0')
- putchar_unlocked (*s++);
- putchar_unlocked ('\n');
-
- if (!intr_context ())
- lock_release (&console_lock);
+ putchar_have_lock (*s++);
+ putchar_have_lock ('\n');
+ release_console ();
return 0;
}
+/* Writes the N characters in BUFFER to the console. */
+void
+putbuf (const char *buffer, size_t n)
+{
+ acquire_console ();
+ while (n-- > 0)
+ putchar_have_lock (*buffer++);
+ release_console ();
+}
+
/* Writes C to the vga display and serial port. */
int
putchar (int c)
{
- if (!intr_context ())
- lock_acquire (&console_lock);
-
- putchar_unlocked (c);
-
- if (!intr_context ())
- lock_release (&console_lock);
-
+ acquire_console ();
+ putchar_have_lock (c);
+ release_console ();
+
return c;
}
\f
{
int *char_cnt = char_cnt_;
(*char_cnt)++;
- putchar_unlocked (c);
+ putchar_have_lock (c);
}
/* Writes C to the vga display and serial port.
The caller has already acquired the console lock if
appropriate. */
static void
-putchar_unlocked (uint8_t c)
+putchar_have_lock (uint8_t c)
{
+ ASSERT (console_locked_by_current_thread ());
+ write_cnt++;
serial_putc (c);
vga_putc (c);
}