semaphores: remove console_sem and make semaphore.c optional
This is incomplete.
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
diff --git a/kernel/Makefile b/kernel/Makefile
index e898c5b..ab7dd786 100644
--- a/kernel/Makefile
+++ b/kernel/Makefile
@@ -8,7 +8,7 @@
signal.o sys.o kmod.o workqueue.o pid.o \
rcupdate.o extable.o params.o posix-timers.o \
kthread.o wait.o kfifo.o sys_ni.o posix-cpu-timers.o mutex.o \
- hrtimer.o rwsem.o nsproxy.o srcu.o semaphore.o \
+ hrtimer.o rwsem.o nsproxy.o srcu.o \
notifier.o ksysfs.o sched_clock.o cred.o \
async.o range.o
obj-y += groups.o
@@ -29,6 +29,7 @@
obj-$(CONFIG_SYSCTL_SYSCALL_CHECK) += sysctl_check.o
obj-$(CONFIG_STACKTRACE) += stacktrace.o
obj-y += time/
+obj-$(CONFIG_LEGACY_SEMAPHORE) += semaphore.o
obj-$(CONFIG_DEBUG_MUTEXES) += mutex-debug.o
obj-$(CONFIG_LOCKDEP) += lockdep.o
ifeq ($(CONFIG_PROC_FS),y)
diff --git a/kernel/printk.c b/kernel/printk.c
index 7982a0a..953a9a5b 100644
--- a/kernel/printk.c
+++ b/kernel/printk.c
@@ -77,25 +77,31 @@
EXPORT_SYMBOL(oops_in_progress);
/*
- * console_sem protects the console_drivers list, and also
+ * The console lock protects the console_drivers list, and also
* provides serialisation for access to the entire console
* driver system.
+ * The lock can be in one of four states, depending on whether
+ * the console is locked and/or suspended. In suspended state,
+ * it is not possible to acquire the lock for output to the
+ * console, but it can still be locked for other purposes.
*/
-static DEFINE_SEMAPHORE(console_sem);
+enum {
+ CONSOLE_UNLOCKED = 0,
+ CONSOLE_LOCKED = 1,
+ CONSOLE_SUSPENDED = 2,
+ CONSOLE_LOCKED_SUSPENDED = 3,
+};
+static atomic_t console_state = ATOMIC_INIT(CONSOLE_UNLOCKED);
+static bool console_set_state(unsigned int old, unsigned int new)
+{
+ return atomic_cmpxchg(&console_state, old, new) == old;
+}
+static DECLARE_WAIT_QUEUE_HEAD(console_wq);
+
struct console *console_drivers;
EXPORT_SYMBOL_GPL(console_drivers);
/*
- * This is used for debugging the mess that is the VT code by
- * keeping track if we have the console semaphore held. It's
- * definitely not the perfect debug tool (we don't know if _WE_
- * hold it are racing, but it helps tracking those weird code
- * path in the console code where we end up in places I want
- * locked without the console sempahore held
- */
-static int console_locked, console_suspended;
-
-/*
* logbuf_lock protects log_buf, log_start, log_end, con_start and logged_chars
* It is also used in interesting ways to provide interlocking in
* console_unlock();.
@@ -691,7 +697,7 @@
/* If a crash is occurring, make sure we can't deadlock */
raw_spin_lock_init(&logbuf_lock);
/* And make sure that we print immediately */
- sema_init(&console_sem, 1);
+ atomic_set(&console_state, CONSOLE_UNLOCKED);
}
#if defined(CONFIG_PRINTK_TIME)
@@ -796,15 +802,14 @@
* in order to do this test safely.
*/
if (!can_use_console(cpu)) {
- console_locked = 0;
+ atomic_set(&console_state, CONSOLE_UNLOCKED);
wake = 1;
retval = 0;
}
}
printk_cpu = UINT_MAX;
if (wake)
- up(&console_sem);
- raw_spin_unlock(&logbuf_lock);
+ wake_up(&console_wq);
return retval;
}
static const char recursion_bug_msg [] =
@@ -1123,17 +1128,16 @@
if (!console_suspend_enabled)
return;
printk("Suspending console(s) (use no_console_suspend to debug)\n");
- console_lock();
- console_suspended = 1;
- up(&console_sem);
+ wait_event(console_wq,
+ console_set_state(CONSOLE_UNLOCKED, CONSOLE_SUSPENDED));
}
void resume_console(void)
{
if (!console_suspend_enabled)
return;
- down(&console_sem);
- console_suspended = 0;
+ wait_event(console_wq,
+ console_set_state(CONSOLE_SUSPENDED, CONSOLE_LOCKED));
console_unlock();
}
@@ -1173,12 +1177,17 @@
*/
void console_lock(void)
{
+ unsigned int state;
BUG_ON(in_interrupt());
- down(&console_sem);
- if (console_suspended)
- return;
- console_locked = 1;
- console_may_schedule = 1;
+
+ /* wait until we transition from unlocked to locked state */
+ state = CONSOLE_UNLOCKED;
+ wait_event(console_wq, !(state = atomic_cmpxchg(&console_state,
+ state & ~CONSOLE_LOCKED,
+ state | CONSOLE_LOCKED)) & CONSOLE_LOCKED);
+ smp_rmb(); /* XXX does atomic_cmpxchg always imply an smp_rmb? */
+ if (state != CONSOLE_SUSPENDED)
+ console_may_schedule = 1;
}
EXPORT_SYMBOL(console_lock);
@@ -1192,21 +1201,26 @@
*/
int console_trylock(void)
{
- if (down_trylock(&console_sem))
+ if (!console_set_state(CONSOLE_UNLOCKED, CONSOLE_LOCKED))
return 0;
- if (console_suspended) {
- up(&console_sem);
- return 0;
- }
- console_locked = 1;
+ smp_rmb();
+
console_may_schedule = 0;
return 1;
}
EXPORT_SYMBOL(console_trylock);
+/*
+ * This is used for debugging the mess that is the VT code by
+ * keeping track if we have the console semaphore held. It's
+ * definitely not the perfect debug tool (we don't know if _WE_
+ * hold it are racing, but it helps tracking those weird code
+ * path in the console code where we end up in places I want
+ * locked without the console sempahore held
+ */
int is_console_locked(void)
{
- return console_locked;
+ return atomic_read(&console_state) != CONSOLE_UNLOCKED;
}
static DEFINE_PER_CPU(int, printk_pending);
@@ -1235,7 +1249,7 @@
/**
* console_unlock - unlock the console system
*
- * Releases the console_lock which the caller holds on the console system
+ * Releases the console lock which the caller holds on the console system
* and the console driver list.
*
* While the console_lock was held, console output may have been buffered
@@ -1252,8 +1266,9 @@
unsigned _con_start, _log_end;
unsigned wake_klogd = 0, retry = 0;
- if (console_suspended) {
- up(&console_sem);
+ if (atomic_read(&console_state) == CONSOLE_LOCKED_SUSPENDED) {
+ atomic_set(&console_state, CONSOLE_SUSPENDED);
+ wake_up(&console_wq);
return;
}
@@ -1274,15 +1289,16 @@
start_critical_timings();
local_irq_restore(flags);
}
- console_locked = 0;
/* Release the exclusive_console once it is used */
if (unlikely(exclusive_console))
exclusive_console = NULL;
+ atomic_set(&console_state, CONSOLE_UNLOCKED);
+
raw_spin_unlock(&logbuf_lock);
- up(&console_sem);
+ wake_up(&console_wq);
/*
* Someone could have filled up the buffer again, so re-check if there's
@@ -1328,12 +1344,13 @@
* oops_in_progress is set to 1..
*/
if (oops_in_progress) {
- if (down_trylock(&console_sem) != 0)
+ if (!console_set_state(CONSOLE_UNLOCKED, CONSOLE_LOCKED) &&
+ !console_set_state(CONSOLE_SUSPENDED, CONSOLE_LOCKED_SUSPENDED))
return;
+ smp_rmb();
} else
console_lock();
- console_locked = 1;
console_may_schedule = 0;
for_each_console(c)
if ((c->flags & CON_ENABLED) && c->unblank)
