> -----邮件原件----- > 发件人: linux-kernel-owner@xxxxxxxxxxxxxxx > [mailto:linux-kernel-owner@xxxxxxxxxxxxxxx] 代表 Greg Kroah-Hartman > 发送时间: 2019年1月31日 18:55 > 收件人: Li,Rongqing <lirongqing@xxxxxxxxx> > 抄送: linux-serial@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; > jslaby@xxxxxxxx; gkohli@xxxxxxxxxxxxxx > 主题: Re: [PATCH][V5] tty: fix race between flush_to_ldisc and tty_open > > On Thu, Jan 31, 2019 at 05:43:16PM +0800, Li RongQing wrote: > > There still is a race window after the commit b027e2298bd588 > > ("tty: fix data race between tty_init_dev and flush of buf"), and we > > encountered this crash issue if receive_buf call comes before tty > > initialization completes in tty_open and > > tty->driver_data may be NULL. > > > > CPU0 CPU1 > > ---- ---- > > tty_open > > tty_init_dev > > tty_ldisc_unlock > > schedule flush_to_ldisc > > receive_buf > > tty_port_default_receive_buf > > tty_ldisc_receive_buf > > n_tty_receive_buf_common > > __receive_buf > > uart_flush_chars > > uart_start > > /*tty->driver_data is NULL*/ > > tty->ops->open > > /*init tty->driver_data*/ > > > > it can be fixed by extending ldisc semaphore lock in tty_init_dev to > > driver_data initialized completely after tty->ops->open(), but this > > will lead to get lock on one function and unlock in some other > > function, and hard to maintain, so fix this race only by checking > > tty->driver_data when receiving, and return if tty->driver_data > > is NULL, and n_tty_receive_buf_common maybe calls uart_unthrottle, so > > add the same check > > > > Signed-off-by: Wang Li <wangli39@xxxxxxxxx> > > Signed-off-by: Zhang Yu <zhangyu31@xxxxxxxxx> > > Signed-off-by: Li RongQing <lirongqing@xxxxxxxxx> > > --- > > V5: move check into uart_start from n_tty_receive_buf_common > > V4: add version information > > V3: not used ldisc semaphore lock, only checking tty->driver_data with > > NULL > > V2: fix building error by EXPORT_SYMBOL tty_ldisc_unlock > > V1: extend ldisc lock to protect that tty->driver_data is inited > > > > drivers/tty/serial/serial_core.c | 6 ++++++ > > 1 file changed, 6 insertions(+) > > > > diff --git a/drivers/tty/serial/serial_core.c > > b/drivers/tty/serial/serial_core.c > > index 5c01bb6d1c24..556f50aa1b58 100644 > > --- a/drivers/tty/serial/serial_core.c > > +++ b/drivers/tty/serial/serial_core.c > > @@ -130,6 +130,9 @@ static void uart_start(struct tty_struct *tty) > > struct uart_port *port; > > unsigned long flags; > > > > + if (!state) > > + return; > > + > > port = uart_port_lock(state, flags); > > __uart_start(tty); > > uart_port_unlock(port, flags); > > @@ -727,6 +730,9 @@ static void uart_unthrottle(struct tty_struct *tty) > > upstat_t mask = UPSTAT_SYNC_FIFO; > > struct uart_port *port; > > > > + if (!state) > > + return; > > + > > port = uart_port_ref(state); > > if (!port) > > return; > > -- > > 2.16.2 > > > Hm, I wrote this patch, not you, right? So shouldn't I get the > credit/blame for it? :) > Welcome you to add your credit/blame/signature and I am not clear the rule, and be afraid to become fake > Also, this is a bug in the serial code, not necessarily the tty layer, > so the subject should change... > > And you did test this, right? I add some delay in tty_init_dev to simulate this issue. it can fix this my issue. Thanks -RongQing > > thanks, > > greg k-h
