There is a deadlock in rs_close(), which is shown
below:
(Thread 1) | (Thread 2)
| rs_open()
rs_close() | mod_timer()
spin_lock_bh() //(1) | (wait a time)
... | rs_poll()
del_timer_sync() | spin_lock() //(2)
(wait timer to stop) | ...
We hold timer_lock in position (1) of thread 1 and
use del_timer_sync() to wait timer to stop, but timer handler
also need timer_lock in position (2) of thread 2.
As a result, rs_close() will block forever.
This patch extracts del_timer_sync() from the protection of
spin_lock_bh(), which could let timer handler to obtain
the needed lock.
Signed-off-by: Duoming Zhou <duoming@xxxxxxxxxx>
---
arch/xtensa/platforms/iss/console.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/arch/xtensa/platforms/iss/console.c b/arch/xtensa/platforms/iss/console.c
index 81d7c7e8f7e..d431b61ae3c 100644
--- a/arch/xtensa/platforms/iss/console.c
+++ b/arch/xtensa/platforms/iss/console.c
@@ -51,8 +51,10 @@ static int rs_open(struct tty_struct *tty, struct file * filp)
static void rs_close(struct tty_struct *tty, struct file * filp)
{
spin_lock_bh(&timer_lock);
- if (tty->count == 1)
+ if (tty->count == 1) {
+ spin_unlock_bh(&timer_lock);
del_timer_sync(&serial_timer);
+ }
spin_unlock_bh(&timer_lock);
}
--
2.17.1
