Hi Patrick,
On 06/27/2015 08:51 PM, Patrick Donnelly wrote:
> task_pgrp requires an rcu or tasklist lock to be obtained if the returned pid
> is to be dereferenced, which kill_pgrp does. Obtain an RCU lock for the
> duration of use.
>
> Signed-off-by: Patrick Donnelly <batr...@batbytes.com>
> ---
> drivers/tty/tty_io.c | 24 +++++++++++++++---------
> 1 file changed, 15 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
> index 57fc6ee..fbb55db 100644
> --- a/drivers/tty/tty_io.c
> +++ b/drivers/tty/tty_io.c
> @@ -388,33 +388,39 @@ EXPORT_SYMBOL_GPL(tty_find_polling_driver);
> int tty_check_change(struct tty_struct *tty)
> {
> unsigned long flags;
> + struct pid *pgrp;
> int ret = 0;
>
> if (current->signal->tty != tty)
> return 0;
>
> - spin_lock_irqsave(&tty->ctrl_lock, flags);
> + rcu_read_lock();
> + pgrp = task_pgrp(current);
>
> + spin_lock_irqsave(&tty->ctrl_lock, flags);
> if (!tty->pgrp) {
> printk(KERN_WARNING "tty_check_change: tty->pgrp == NULL!\n");
> - goto out_unlock;
> + goto out_irqunlock;
The label name changing is not really necessary and would reduce diff count.
It would be nice to get the printk() out from the locks as well (in a follow-on
patch?)
Regards,
Peter Hurley
> }
> - if (task_pgrp(current) == tty->pgrp)
> - goto out_unlock;
> + if (pgrp == tty->pgrp)
> + goto out_irqunlock;
> spin_unlock_irqrestore(&tty->ctrl_lock, flags);
> +
> if (is_ignored(SIGTTOU))
> - goto out;
> + goto out_rcuunlock;
> if (is_current_pgrp_orphaned()) {
> ret = -EIO;
> - goto out;
> + goto out_rcuunlock;
> }
> - kill_pgrp(task_pgrp(current), SIGTTOU, 1);
> + kill_pgrp(pgrp, SIGTTOU, 1);
> + rcu_read_unlock();
> set_thread_flag(TIF_SIGPENDING);
> ret = -ERESTARTSYS;
> -out:
> return ret;
> -out_unlock:
> +out_irqunlock:
> spin_unlock_irqrestore(&tty->ctrl_lock, flags);
> +out_rcuunlock:
> + rcu_read_unlock();
> return ret;
> }
>
>
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