Hello, On Thu, 7 Apr 2022 09:02:05 +0200 Jiri Slaby wrote: > > 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); > > Unlocking the lock at this point doesn't look safe at all. Maybe moving > the timer deletion before the lock? There is no current maintainer to > ask. Most of the driver originates from rmk. Ccing him just in case. Thanks a lot for your time and advice. I think moving the del_timer_sync() before the lock is good. Because we may use "sa1100_enable_ms(&sport->port)" to start the timer after we have set termios. > FWIW the lock was moved by this commit around linux 2.5.55 (from > full-history-linux [1]) > commit f38aef3e62c26a33ea360a86fde9b27e183a3748 > Author: Russell King <rmk@xxxxxxxxxxxxxxxxxxxxxx> > Date: Fri Jan 3 15:42:09 2003 +0000 > > [SERIAL] Convert change_speed() to settermios() > > [1] > https://archive.org/download/git-history-of-linux/full-history-linux.git.tar > > > del_timer_sync(&sport->timer); > > + spin_lock_irqsave(&sport->port.lock, flags); > > > > /* > > * Update the per-port timeout. Best regards, Duoming Zhou
