From: Ben Pfaff Date: Wed, 22 Sep 2004 07:16:11 +0000 (+0000) Subject: Make console lock recursive. X-Git-Url: https://pintos-os.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=b567bc2c70ab0e4146fc208bd30224d76ea1cf5f;p=pintos-anon Make console lock recursive. --- diff --git a/src/lib/kernel/console.c b/src/lib/kernel/console.c index 149f29c..14c707a 100644 --- a/src/lib/kernel/console.c +++ b/src/lib/kernel/console.c @@ -16,12 +16,65 @@ static void putchar_unlocked (uint8_t c); from mixing their output, which looks confusing. */ static struct lock 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() + schedule_tail() - another thread dying as we switch threads + schedule() + thread_yield() + intr_handler() - timer interrupt + intr_set_level() + serial_putc() + putchar_unlocked() + 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; + +/* Initializes the console. */ void console_init (void) { lock_init (&console_lock, "console"); } +/* Acquires the console lock. */ +static void +acquire_console (void) +{ + if (!intr_context ()) + { + 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 ()) + { + if (console_lock_depth > 0) + console_lock_depth--; + else + lock_release (&console_lock); + } +} + /* The standard vprintf() function, which is like printf() but uses a va_list. Writes its output to both vga display and serial port. */ @@ -30,13 +83,9 @@ vprintf (const char *format, va_list args) { 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; } @@ -46,15 +95,11 @@ vprintf (const char *format, va_list args) 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); + release_console (); return 0; } @@ -63,28 +108,20 @@ puts (const char *s) void putbuf (const char *buffer, size_t n) { - if (!intr_context ()) - lock_acquire (&console_lock); - + acquire_console (); while (n-- > 0) putchar_unlocked (*buffer++); - - if (!intr_context ()) - lock_release (&console_lock); + release_console (); } /* Writes C to the vga display and serial port. */ int putchar (int c) { - if (!intr_context ()) - lock_acquire (&console_lock); - + acquire_console (); putchar_unlocked (c); - - if (!intr_context ()) - lock_release (&console_lock); - + release_console (); + return c; }