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 extracts del_timer_sync() from the protection of
spin_lock_irqsave(), which could let timer handler to obtain
the needed lock.
Signed-off-by: Duoming Zhou <duoming@xxxxxxxxxx>
---
drivers/tty/serial/sa1100.c | 2 ++
1 file changed, 2 insertions(+)
diff --git a/drivers/tty/serial/sa1100.c b/drivers/tty/serial/sa1100.c
index 5fe6cccfc1a..3a5f12ced0b 100644
--- a/drivers/tty/serial/sa1100.c
+++ b/drivers/tty/serial/sa1100.c
@@ -476,7 +476,9 @@ sa1100_set_termios(struct uart_port *port, struct ktermios *termios,
UTSR1_TO_SM(UTSR1_ROR);
}
+ spin_unlock_irqrestore(&sport->port.lock, flags);
del_timer_sync(&sport->timer);
+ spin_lock_irqsave(&sport->port.lock, flags);
/*
* Update the per-port timeout.
--
2.17.1
