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arch: xtensa: platforms: Fix deadlock in rs_close() 

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>
This commit is contained in:
Duoming Zhou 2022-04-07 23:44:30 +08:00 committed by Max Filippov
parent ee69d4be8f
commit eb5adc7075
1 changed files with 0 additions and 8 deletions
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8
arch/xtensa/platforms/iss/console.c
View File

@ -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);
}