On Wed, Nov 20, 2019 at 04:44:50PM +0100, Greg Kroah-Hartman wrote: > On Wed, Nov 20, 2019 at 03:17:09PM +0000, Sudip Mukherjee wrote: > > There seems to be a race condition in tty drivers and I could see on > > many boot cycles a NULL pointer dereference as tty_init_dev() tries to > > do 'tty->port->itty = tty' even though tty->port is NULL. <snip> > > +++ b/drivers/tty/pty.c > > @@ -842,7 +842,7 @@ static int ptmx_open(struct inode *inode, struct file *filp) > > > > > > mutex_lock(&tty_mutex); > > - tty = tty_init_dev(ptm_driver, index); > > + tty = tty_init_dev(ptm_driver, index, 0); > > Horrible naming scheme for this new "flag". > > Look at that call here, can you instantly tell what this call is doing > with "0"? I sure can not :( well, I also made the mistake of 1->0 in my initial patch. :( > > If you really want to do this, you make a different function, > tty_init_dev_retry() and then have that pass in a retry flag in the tty > core, so that any users always know what they are doing here. will do. > > But, this really feels like a race in the code somewhere: > > > --- a/drivers/tty/tty_io.c > > +++ b/drivers/tty/tty_io.c > > @@ -1295,6 +1295,7 @@ static int tty_reopen(struct tty_struct *tty) > > * tty_init_dev - initialise a tty device > > * @driver: tty driver we are opening a device on > > * @idx: device index > > + * @retry: retry count if driver has not set tty->port yet > > Why would tty->port not be set up already? The caller has control over > this, what is not happening correctly to cause this? Will add more debugs to check what is happening now and then send you v2. -- Regards Sudip
