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drivers: tty: serial: Fix deadlock in sa1100_set_termios()

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[ Upstream commit 62b2caef400c1738b6d22f636c628d9f85cd4c4c ]

There is a deadlock in sa1100_set_termios(), which is shown
below:

   (Thread 1)              |      (Thread 2)
                           | sa1100_enable_ms()
sa1100_set_termios()       |  mod_timer()
 spin_lock_irqsave() //(1) |  (wait a time)
 ...                       | sa1100_timeout()
 del_timer_sync()          |  spin_lock_irqsave() //(2)
 (wait timer to stop)      |  ...

We hold sport->port.lock in position (1) of thread 1 and
use del_timer_sync() to wait timer to stop, but timer handler
also need sport->port.lock in position (2) of thread 2. As a result,
sa1100_set_termios() will block forever.

This patch moves del_timer_sync() before spin_lock_irqsave()
in order to prevent the deadlock.

Signed-off-by: Duoming Zhou <duoming@zju.edu.cn>
Link: https://lore.kernel.org/r/20220417111626.7802-1-duoming@zju.edu.cn
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
Duoming Zhou 2022-04-17 19:16:26 +08:00 committed by Greg Kroah-Hartman
parent c91a74b1f0
commit 09a5958a24
1 changed files with 2 additions and 2 deletions
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4
drivers/tty/serial/sa1100.c
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@ -454,6 +454,8 @@ sa1100_set_termios(struct uart_port *port, struct ktermios *termios,
baud = uart_get_baud_rate(port, termios, old, 0, port->uartclk/16);
quot = uart_get_divisor(port, baud);
del_timer_sync(&sport->timer);
spin_lock_irqsave(&sport->port.lock, flags);
sport->port.read_status_mask &= UTSR0_TO_SM(UTSR0_TFS);
@ -484,8 +486,6 @@ sa1100_set_termios(struct uart_port *port, struct ktermios *termios,
UTSR1_TO_SM(UTSR1_ROR);
}
del_timer_sync(&sport->timer);
/*
* Update the per-port timeout.
*/