[PATCH 06/10] tty: annotate tty_write_lock

[Arnd Bergmann]

atomic_write_lock never nests below BTM, so
there are no lock order problems between the
two.

Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
---
 drivers/char/tty_io.c |    5 +++++
 1 files changed, 5 insertions(+), 0 deletions(-)

diff --git a/drivers/char/tty_io.c b/drivers/char/tty_io.c
index d51993b..36aecba 100644
--- a/drivers/char/tty_io.c
+++ b/drivers/char/tty_io.c
@@ -912,6 +912,11 @@ void tty_write_unlock(struct tty_struct *tty)
 
 int tty_write_lock(struct tty_struct *tty, int ndelay)
 {
+	/*
+	 * code inspection has shown that this is never called
+	 * with the BTM held. Make sure this stays that way.
+	 */
+	WARN_ON_ONCE(tty_locked());
 	if (!mutex_trylock(&tty->atomic_write_lock)) {
 		if (ndelay)
 			return -EAGAIN;
-- 
1.7.0.4

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