From: Duoming Zhou duoming@zju.edu.cn
[ Upstream commit eb5adc70754d26a260f8b42d39db42da0d0af500 ]
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 deletes the redundant timer_lock in order to prevent the deadlock. Because there is no race condition between rs_close, rs_open and rs_poll.
Signed-off-by: Duoming Zhou duoming@zju.edu.cn Message-Id: 20220407154430.22387-1-duoming@zju.edu.cn Signed-off-by: Max Filippov jcmvbkbc@gmail.com Signed-off-by: Sasha Levin sashal@kernel.org --- arch/xtensa/platforms/iss/console.c | 8 -------- 1 file changed, 8 deletions(-)
diff --git a/arch/xtensa/platforms/iss/console.c b/arch/xtensa/platforms/iss/console.c index 81d7c7e8f7e9..10b79d3c74e0 100644 --- a/arch/xtensa/platforms/iss/console.c +++ b/arch/xtensa/platforms/iss/console.c @@ -36,24 +36,19 @@ static void rs_poll(struct timer_list *); static struct tty_driver *serial_driver; static struct tty_port serial_port; static DEFINE_TIMER(serial_timer, rs_poll); -static DEFINE_SPINLOCK(timer_lock);
static int rs_open(struct tty_struct *tty, struct file * filp) { - spin_lock_bh(&timer_lock); if (tty->count == 1) mod_timer(&serial_timer, jiffies + SERIAL_TIMER_VALUE); - spin_unlock_bh(&timer_lock);
return 0; }
static void rs_close(struct tty_struct *tty, struct file * filp) { - spin_lock_bh(&timer_lock); if (tty->count == 1) del_timer_sync(&serial_timer); - spin_unlock_bh(&timer_lock); }
@@ -73,8 +68,6 @@ static void rs_poll(struct timer_list *unused) int rd = 1; unsigned char c;
- spin_lock(&timer_lock); - while (simc_poll(0)) { rd = simc_read(0, &c, 1); if (rd <= 0) @@ -87,7 +80,6 @@ static void rs_poll(struct timer_list *unused) tty_flip_buffer_push(port); if (rd) mod_timer(&serial_timer, jiffies + SERIAL_TIMER_VALUE); - spin_unlock(&timer_lock); }