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arch: xtensa: platforms: Fix deadlock in rs_close()
[ Upstream commit eb5adc7075
]
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>
This commit is contained in:
parent
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commit
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1 changed files with 0 additions and 8 deletions
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@ -36,24 +36,19 @@ static void rs_poll(struct timer_list *);
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static struct tty_driver *serial_driver;
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static struct tty_port serial_port;
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static DEFINE_TIMER(serial_timer, rs_poll);
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static DEFINE_SPINLOCK(timer_lock);
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static int rs_open(struct tty_struct *tty, struct file * filp)
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{
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spin_lock_bh(&timer_lock);
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if (tty->count == 1)
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mod_timer(&serial_timer, jiffies + SERIAL_TIMER_VALUE);
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spin_unlock_bh(&timer_lock);
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return 0;
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}
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static void rs_close(struct tty_struct *tty, struct file * filp)
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{
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spin_lock_bh(&timer_lock);
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if (tty->count == 1)
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del_timer_sync(&serial_timer);
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spin_unlock_bh(&timer_lock);
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}
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@ -73,8 +68,6 @@ static void rs_poll(struct timer_list *unused)
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int rd = 1;
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unsigned char c;
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spin_lock(&timer_lock);
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while (simc_poll(0)) {
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rd = simc_read(0, &c, 1);
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if (rd <= 0)
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@ -87,7 +80,6 @@ static void rs_poll(struct timer_list *unused)
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tty_flip_buffer_push(port);
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if (rd)
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mod_timer(&serial_timer, jiffies + SERIAL_TIMER_VALUE);
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spin_unlock(&timer_lock);
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}
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