tty: Hold write ldisc sem in tty_reopen()

index 0c98d88f795a..b989ca26fc78 100644
@@ -293,6 +293,16 @@ down_write_failed(struct ld_semaphore *sem, long count, long timeout)
 	if (!locked)
 		atomic_long_add_return(-LDSEM_WAIT_BIAS, &sem->count);
 	list_del(&waiter.list);
+
+	/*
+	 * In case of timeout, wake up every reader who gave the right of way
+	 * to writer. Prevent separation readers into two groups:
+	 * one that helds semaphore and another that sleeps.
+	 * (in case of no contention with a writer)
+	 */
+	if (!locked && list_empty(&sem->write_wait))
+		__ldsem_wake_readers(sem);
+
 	raw_spin_unlock_irq(&sem->wait_lock);
 
 	__set_current_state(TASK_RUNNING);

index ee80dfbd5442..f73d8fa7f02b 100644
@@ -1268,15 +1268,20 @@ static int tty_reopen(struct tty_struct *tty)
 	if (test_bit(TTY_EXCLUSIVE, &tty->flags) && !capable(CAP_SYS_ADMIN))
 		return -EBUSY;
 
-	tty->count++;
+	retval = tty_ldisc_lock(tty, 5 * HZ);
+	if (retval)
+		return retval;
 
+	tty->count++;
 	if (tty->ldisc)
-		return 0;
+		goto out_unlock;
 
 	retval = tty_ldisc_reinit(tty, tty->termios.c_line);
 	if (retval)
 		tty->count--;
 
+out_unlock:
+	tty_ldisc_unlock(tty);
 	return retval;
 }
 

index dabb391909aa..99460af61b77 100644
@@ -612,7 +612,7 @@ static ssize_t n_hdlc_tty_read(struct tty_struct *tty, struct file *file,
 		}
 			
 		/* no data */
-		if (file->f_flags & O_NONBLOCK) {
+		if (tty_io_nonblock(tty, file)) {
 			ret = -EAGAIN;
 			break;
 		}

@@ -679,7 +679,7 @@ static ssize_t n_hdlc_tty_write(struct tty_struct *tty, struct file *file,
 		if (tbuf)
 			break;
 
-		if (file->f_flags & O_NONBLOCK) {
+		if (tty_io_nonblock(tty, file)) {
 			error = -EAGAIN;
 			break;
 		}

index 749a608c40b0..f75696f0ee2d 100644
@@ -1085,7 +1085,7 @@ static ssize_t r3964_read(struct tty_struct *tty, struct file *file,
 		pMsg = remove_msg(pInfo, pClient);
 		if (pMsg == NULL) {
 			/* no messages available. */
-			if (file->f_flags & O_NONBLOCK) {
+			if (tty_io_nonblock(tty, file)) {
 				ret = -EAGAIN;
 				goto unlock;
 			}

index 3ad460219fd6..5dc9686697cf 100644
@@ -1702,7 +1702,7 @@ n_tty_receive_buf_common(struct tty_struct *tty, const unsigned char *cp,
 
 	down_read(&tty->termios_rwsem);
 
-	while (1) {
+	do {
 		/*
 		 * When PARMRK is set, each input char may take up to 3 chars
 		 * in the read buf; reduce the buffer space avail by 3x

@@ -1744,7 +1744,7 @@ n_tty_receive_buf_common(struct tty_struct *tty, const unsigned char *cp,
 			fp += n;
 		count -= n;
 		rcvd += n;
-	}
+	} while (!test_bit(TTY_LDISC_CHANGING, &tty->flags));
 
 	tty->receive_room = room;
 

@@ -2211,7 +2211,7 @@ static ssize_t n_tty_read(struct tty_struct *tty, struct file *file,
 					break;
 				if (!timeout)
 					break;
-				if (file->f_flags & O_NONBLOCK) {
+				if (tty_io_nonblock(tty, file)) {
 					retval = -EAGAIN;
 					break;
 				}

@@ -2365,7 +2365,7 @@ static ssize_t n_tty_write(struct tty_struct *tty, struct file *file,
 		}
 		if (!nr)
 			break;
-		if (file->f_flags & O_NONBLOCK) {
+		if (tty_io_nonblock(tty, file)) {
 			retval = -EAGAIN;
 			break;
 		}

index fc4c97cae01e..9434d20cf3ca 100644
@@ -327,6 +327,11 @@ int tty_ldisc_lock(struct tty_struct *tty, unsigned long timeout)
 {
 	int ret;
 
+	/* Kindly asking blocked readers to release the read side */
+	set_bit(TTY_LDISC_CHANGING, &tty->flags);
+	wake_up_interruptible_all(&tty->read_wait);
+	wake_up_interruptible_all(&tty->write_wait);
+
 	ret = __tty_ldisc_lock(tty, timeout);
 	if (!ret)
 		return -EBUSY;

@@ -337,6 +342,8 @@ int tty_ldisc_lock(struct tty_struct *tty, unsigned long timeout)
 void tty_ldisc_unlock(struct tty_struct *tty)
 {
 	clear_bit(TTY_LDISC_HALTED, &tty->flags);
+	/* Can be cleared here - ldisc_unlock will wake up writers firstly */
+	clear_bit(TTY_LDISC_CHANGING, &tty->flags);
 	__tty_ldisc_unlock(tty);
 }
 

index 414db2bce715..80ae5528ef8e 100644
@@ -366,6 +366,7 @@ struct tty_file_private {
 #define TTY_NO_WRITE_SPLIT 	17	/* Preserve write boundaries to driver */
 #define TTY_HUPPED 		18	/* Post driver->hangup() */
 #define TTY_HUPPING		19	/* Hangup in progress */
+#define TTY_LDISC_CHANGING	20	/* Change pending - non-block IO */
 #define TTY_LDISC_HALTED	22	/* Line discipline is halted */
 
 /* Values for tty->flow_change */

@@ -383,6 +384,12 @@ static inline void tty_set_flow_change(struct tty_struct *tty, int val)
 	smp_mb();
 }
 
+static inline bool tty_io_nonblock(struct tty_struct *tty, struct file *file)
+{
+	return file->f_flags & O_NONBLOCK ||
+		test_bit(TTY_LDISC_CHANGING, &tty->flags);
+}
+
 static inline bool tty_io_error(struct tty_struct *tty)
 {
 	return test_bit(TTY_IO_ERROR, &tty->flags);

index f73d8fa7f02b..57d06eda5b2f 100644
@@ -1272,16 +1272,13 @@ static int tty_reopen(struct tty_struct *tty)
 	if (retval)
 		return retval;
 
-	tty->count++;
-	if (tty->ldisc)
-		goto out_unlock;
+	if (!tty->ldisc)
+		retval = tty_ldisc_reinit(tty, tty->termios.c_line);
+	tty_ldisc_unlock(tty);
 
-	retval = tty_ldisc_reinit(tty, tty->termios.c_line);
-	if (retval)
-		tty->count--;
+	if (retval == 0)
+		tty->count++;
 
-out_unlock:
-	tty_ldisc_unlock(tty);
 	return retval;
 }
 

index b989ca26fc78..d4d0dbf4a6d9 100644
@@ -34,29 +34,6 @@
 #include <linux/sched/task.h>
 
 
-#ifdef CONFIG_DEBUG_LOCK_ALLOC
-# define __acq(l, s, t, r, c, n, i)		\
-				lock_acquire(&(l)->dep_map, s, t, r, c, n, i)
-# define __rel(l, n, i)				\
-				lock_release(&(l)->dep_map, n, i)
-#define lockdep_acquire(l, s, t, i)		__acq(l, s, t, 0, 1, NULL, i)
-#define lockdep_acquire_nest(l, s, t, n, i)	__acq(l, s, t, 0, 1, n, i)
-#define lockdep_acquire_read(l, s, t, i)	__acq(l, s, t, 1, 1, NULL, i)
-#define lockdep_release(l, n, i)		__rel(l, n, i)
-#else
-# define lockdep_acquire(l, s, t, i)		do { } while (0)
-# define lockdep_acquire_nest(l, s, t, n, i)	do { } while (0)
-# define lockdep_acquire_read(l, s, t, i)	do { } while (0)
-# define lockdep_release(l, n, i)		do { } while (0)
-#endif
-
-#ifdef CONFIG_LOCK_STAT
-# define lock_stat(_lock, stat)		lock_##stat(&(_lock)->dep_map, _RET_IP_)
-#else
-# define lock_stat(_lock, stat)		do { } while (0)
-#endif
-
-
 #if BITS_PER_LONG == 64
 # define LDSEM_ACTIVE_MASK	0xffffffffL
 #else

@@ -320,17 +297,17 @@ static int __ldsem_down_read_nested(struct ld_semaphore *sem,
 {
 	long count;
 
-	lockdep_acquire_read(sem, subclass, 0, _RET_IP_);
+	rwsem_acquire_read(&sem->dep_map, subclass, 0, _RET_IP_);
 
 	count = atomic_long_add_return(LDSEM_READ_BIAS, &sem->count);
 	if (count <= 0) {
-		lock_stat(sem, contended);
+		lock_contended(&sem->dep_map, _RET_IP_);
 		if (!down_read_failed(sem, count, timeout)) {
-			lockdep_release(sem, 1, _RET_IP_);
+			rwsem_release(&sem->dep_map, 1, _RET_IP_);
 			return 0;
 		}
 	}
-	lock_stat(sem, acquired);
+	lock_acquired(&sem->dep_map, _RET_IP_);
 	return 1;
 }
 

@@ -339,17 +316,17 @@ static int __ldsem_down_write_nested(struct ld_semaphore *sem,
 {
 	long count;
 
-	lockdep_acquire(sem, subclass, 0, _RET_IP_);
+	rwsem_acquire(&sem->dep_map, subclass, 0, _RET_IP_);
 
 	count = atomic_long_add_return(LDSEM_WRITE_BIAS, &sem->count);
 	if ((count & LDSEM_ACTIVE_MASK) != LDSEM_ACTIVE_BIAS) {
-		lock_stat(sem, contended);
+		lock_contended(&sem->dep_map, _RET_IP_);
 		if (!down_write_failed(sem, count, timeout)) {
-			lockdep_release(sem, 1, _RET_IP_);
+			rwsem_release(&sem->dep_map, 1, _RET_IP_);
 			return 0;
 		}
 	}
-	lock_stat(sem, acquired);
+	lock_acquired(&sem->dep_map, _RET_IP_);
 	return 1;
 }
 

@@ -372,8 +349,8 @@ int ldsem_down_read_trylock(struct ld_semaphore *sem)
 
 	while (count >= 0) {
 		if (atomic_long_try_cmpxchg(&sem->count, &count, count + LDSEM_READ_BIAS)) {
-			lockdep_acquire_read(sem, 0, 1, _RET_IP_);
-			lock_stat(sem, acquired);
+			rwsem_acquire_read(&sem->dep_map, 0, 1, _RET_IP_);
+			lock_acquired(&sem->dep_map, _RET_IP_);
 			return 1;
 		}
 	}

@@ -398,8 +375,8 @@ int ldsem_down_write_trylock(struct ld_semaphore *sem)
 
 	while ((count & LDSEM_ACTIVE_MASK) == 0) {
 		if (atomic_long_try_cmpxchg(&sem->count, &count, count + LDSEM_WRITE_BIAS)) {
-			lockdep_acquire(sem, 0, 1, _RET_IP_);
-			lock_stat(sem, acquired);
+			rwsem_acquire(&sem->dep_map, 0, 1, _RET_IP_);
+			lock_acquired(&sem->dep_map, _RET_IP_);
 			return 1;
 		}
 	}

@@ -413,7 +390,7 @@ void ldsem_up_read(struct ld_semaphore *sem)
 {
 	long count;
 
-	lockdep_release(sem, 1, _RET_IP_);
+	rwsem_release(&sem->dep_map, 1, _RET_IP_);
 
 	count = atomic_long_add_return(-LDSEM_READ_BIAS, &sem->count);
 	if (count < 0 && (count & LDSEM_ACTIVE_MASK) == 0)

@@ -427,7 +404,7 @@ void ldsem_up_write(struct ld_semaphore *sem)
 {
 	long count;
 
-	lockdep_release(sem, 1, _RET_IP_);
+	rwsem_release(&sem->dep_map, 1, _RET_IP_);
 
 	count = atomic_long_add_return(-LDSEM_WRITE_BIAS, &sem->count);
 	if (count < 0)

index 9434d20cf3ca..45eda69b150c 100644
@@ -478,6 +478,7 @@ static int tty_ldisc_open(struct tty_struct *tty, struct tty_ldisc *ld)
 
 static void tty_ldisc_close(struct tty_struct *tty, struct tty_ldisc *ld)
 {
+	lockdep_assert_held_exclusive(&tty->ldisc_sem);
 	WARN_ON(!test_bit(TTY_LDISC_OPEN, &tty->flags));
 	clear_bit(TTY_LDISC_OPEN, &tty->flags);
 	if (ld->ops->close)

@@ -499,6 +500,7 @@ static int tty_ldisc_failto(struct tty_struct *tty, int ld)
 	struct tty_ldisc *disc = tty_ldisc_get(tty, ld);
 	int r;
 
+	lockdep_assert_held_exclusive(&tty->ldisc_sem);
 	if (IS_ERR(disc))
 		return PTR_ERR(disc);
 	tty->ldisc = disc;

@@ -622,6 +624,7 @@ EXPORT_SYMBOL_GPL(tty_set_ldisc);
  */
 static void tty_ldisc_kill(struct tty_struct *tty)
 {
+	lockdep_assert_held_exclusive(&tty->ldisc_sem);
 	if (!tty->ldisc)
 		return;
 	/*

@@ -669,6 +672,7 @@ int tty_ldisc_reinit(struct tty_struct *tty, int disc)
 	struct tty_ldisc *ld;
 	int retval;
 
+	lockdep_assert_held_exclusive(&tty->ldisc_sem);
 	ld = tty_ldisc_get(tty, disc);
 	if (IS_ERR(ld)) {
 		BUG_ON(disc == N_TTY);

@@ -767,6 +771,10 @@ int tty_ldisc_setup(struct tty_struct *tty, struct tty_struct *o_tty)
 		return retval;
 
 	if (o_tty) {
+		/*
+		 * Called without o_tty->ldisc_sem held, as o_tty has been
+		 * just allocated and no one has a reference to it.
+		 */
 		retval = tty_ldisc_open(o_tty, o_tty->ldisc);
 		if (retval) {
 			tty_ldisc_close(tty, tty->ldisc);

@@ -832,6 +840,7 @@ int tty_ldisc_init(struct tty_struct *tty)
  */
 void tty_ldisc_deinit(struct tty_struct *tty)
 {
+	/* no ldisc_sem, tty is being destroyed */
 	if (tty->ldisc)
 		tty_ldisc_put(tty->ldisc);
 	tty->ldisc = NULL;

index d4d0dbf4a6d9..717292c1c0df 100644
@@ -212,6 +212,7 @@ down_read_failed(struct ld_semaphore *sem, long count, long timeout)
 		raw_spin_lock_irq(&sem->wait_lock);
 		if (waiter.task) {
 			atomic_long_add_return(-LDSEM_WAIT_BIAS, &sem->count);
+			sem->wait_readers--;
 			list_del(&waiter.list);
 			raw_spin_unlock_irq(&sem->wait_lock);
 			put_task_struct(waiter.task);