Messages in this thread | | | Date | Wed, 15 Dec 2021 07:49:04 +0100 | Subject | Re: [PATCH v2] tty: rpmsg: Fix race condition releasing tty port | From | Jiri Slaby <> |
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Hi,
much better IMO.
On 14. 12. 21, 18:06, Arnaud Pouliquen wrote: > In current implementation the tty_port struct is part of the > rpmsg_tty_port structure.The issue is that the rpmsg_tty_port structure is > freed on rpmsg_tty_remove but also referenced in the tty_struct. > Its release is not predictable due to workqueues. > > For instance following ftrace shows that rpmsg_tty_close is called after > rpmsg_tty_release_cport: ... > diff --git a/drivers/tty/rpmsg_tty.c b/drivers/tty/rpmsg_tty.c > index dae2a4e44f38..69272ad92266 100644 > --- a/drivers/tty/rpmsg_tty.c > +++ b/drivers/tty/rpmsg_tty.c > @@ -53,9 +53,19 @@ static int rpmsg_tty_install(struct tty_driver *driver, struct tty_struct *tty) > > tty->driver_data = cport; > > + tty_port_get(&cport->port);
Can't this fail? Like when racing with removal?
> return tty_port_install(&cport->port, driver, tty); > } ... > static struct rpmsg_tty_port *rpmsg_tty_alloc_cport(void) > @@ -139,6 +156,8 @@ static struct rpmsg_tty_port *rpmsg_tty_alloc_cport(void) > > static void rpmsg_tty_release_cport(struct rpmsg_tty_port *cport) > { > + tty_port_destroy(&cport->port); > +
You should not call tty_port_destroy when you use refcounting. The port is already destroyed when ->destruct() is called. (It has currently no bad effect calling it twice on a port though.)
> @@ -146,7 +165,17 @@ static void rpmsg_tty_release_cport(struct rpmsg_tty_port *cport) > kfree(cport); > } > > -static const struct tty_port_operations rpmsg_tty_port_ops = { }; > +static void rpmsg_tty_destruct_port(struct tty_port *port) > +{ > + struct rpmsg_tty_port *cport = container_of(port, struct rpmsg_tty_port, port); > + > + rpmsg_tty_release_cport(cport); > +} > + > +static const struct tty_port_operations rpmsg_tty_port_ops = { > + .destruct = rpmsg_tty_destruct_port, > +}; > + > > static int rpmsg_tty_probe(struct rpmsg_device *rpdev) > { > @@ -179,7 +208,6 @@ static int rpmsg_tty_probe(struct rpmsg_device *rpdev) > return 0; > > err_destroy: > - tty_port_destroy(&cport->port); > rpmsg_tty_release_cport(cport);
Couldn't you just put the port here? And inline rpmsg_tty_release_cport into the new rpmsg_tty_destruct_port?
thanks, -- js suse labs
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