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From: Arnd Bergmann on 4 May 2010 18:40
atomic_write_lock never nests below BTM as far
as I can tell, so this can eventually get
reverted again unless it triggers bugs.

Signed-off-by: Arnd Bergmann <arnd(a)arndb.de>
---
drivers/char/tty_io.c | 9 +++++++--
1 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/drivers/char/tty_io.c b/drivers/char/tty_io.c
index 3bf2c75..8331dd3 100644
--- a/drivers/char/tty_io.c
+++ b/drivers/char/tty_io.c
@@ -912,10 +912,15 @@ 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;
- if (mutex_lock_interruptible(&tty->atomic_write_lock))
+ if (mutex_lock_interruptible_tty(&tty->atomic_write_lock))
return -ERESTARTSYS;
}
return 0;
@@ -1024,7 +1029,7 @@ out:
void tty_write_message(struct tty_struct *tty, char *msg)
{
if (tty) {
- mutex_lock(&tty->atomic_write_lock);
+ mutex_lock_tty_off(&tty->atomic_write_lock);
tty_lock();
if (tty->ops->write && !test_bit(TTY_CLOSING, &tty->flags)) {
tty_unlock();
--
1.7.0.4

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Next: [PATCH 13/13] tty: turn ldisc_mutex into a regular mutex