lkml.org 
[lkml]   [2021]   [Dec]   [15]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
SubjectRe: [PATCH v2] tty: rpmsg: Fix race condition releasing tty port
From
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

\
 
 \ /
  Last update: 2021-12-15 07:50    [W:0.066 / U:1.148 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site