tty: Fix PPP hang under load (c9b3976e) · Commits · e / devices / android_kernel_fairphone_FP4

drivers/char/tty_ldisc.c

+21 −9

Original line number	Diff line number	Diff line
		@@ -316,8 +316,7 @@ struct tty_ldisc tty_ldisc_ref_wait(struct tty_struct tty)
		{
		/* wait_event is a macro */
		wait_event(tty_ldisc_wait, tty_ldisc_try(tty));
		if (tty->ldisc.refcount == 0)
		printk(KERN_ERR "tty_ldisc_ref_wait\n");
		WARN_ON(tty->ldisc.refcount == 0);
		return &tty->ldisc;
		}

		@@ -376,15 +375,17 @@ EXPORT_SYMBOL_GPL(tty_ldisc_deref);
		* @tty: terminal to activate ldisc on
		*
		* Set the TTY_LDISC flag when the line discipline can be called
		* again. Do necessary wakeups for existing sleepers.
		* again. Do necessary wakeups for existing sleepers. Clear the LDISC
		* changing flag to indicate any ldisc change is now over.
		*
		* Note: nobody should set this bit except via this function. Clearing
		* directly is allowed.
		* Note: nobody should set the TTY_LDISC bit except via this function.
		* Clearing directly is allowed.
		*/

		void tty_ldisc_enable(struct tty_struct *tty)
		{
		set_bit(TTY_LDISC, &tty->flags);
		clear_bit(TTY_LDISC_CHANGING, &tty->flags);
		wake_up(&tty_ldisc_wait);
		}

		@@ -496,7 +497,14 @@ int tty_set_ldisc(struct tty_struct *tty, int ldisc)
		* reference to the line discipline. The TTY_LDISC bit
		* prevents anyone taking a reference once it is clear.
		* We need the lock to avoid racing reference takers.
		*
		* We must clear the TTY_LDISC bit here to avoid a livelock
		* with a userspace app continually trying to use the tty in
		* parallel to the change and re-referencing the tty.
		*/
		clear_bit(TTY_LDISC, &tty->flags);
		if (o_tty)
		clear_bit(TTY_LDISC, &o_tty->flags);

		spin_lock_irqsave(&tty_ldisc_lock, flags);
		if (tty->ldisc.refcount \|\| (o_tty && o_tty->ldisc.refcount)) {
		@@ -528,7 +536,7 @@ int tty_set_ldisc(struct tty_struct *tty, int ldisc)
		* If the TTY_LDISC bit is set, then we are racing against
		* another ldisc change
		*/
		if (!test_bit(TTY_LDISC, &tty->flags)) {
		if (test_bit(TTY_LDISC_CHANGING, &tty->flags)) {
		struct tty_ldisc *ld;
		spin_unlock_irqrestore(&tty_ldisc_lock, flags);
		tty_ldisc_put(new_ldisc.ops);
		@@ -536,10 +544,14 @@ int tty_set_ldisc(struct tty_struct *tty, int ldisc)
		tty_ldisc_deref(ld);
		goto restart;
		}

		clear_bit(TTY_LDISC, &tty->flags);
		/*
		* This flag is used to avoid two parallel ldisc changes. Once
		* open and close are fine grained locked this may work better
		* as a mutex shared with the open/close/hup paths
		*/
		set_bit(TTY_LDISC_CHANGING, &tty->flags);
		if (o_tty)
		clear_bit(TTY_LDISC, &o_tty->flags);
		set_bit(TTY_LDISC_CHANGING, &o_tty->flags);
		spin_unlock_irqrestore(&tty_ldisc_lock, flags);

		/*

include/linux/tty.h

+1 −0

Original line number	Diff line number	Diff line
		@@ -301,6 +301,7 @@ struct tty_struct {
		#define TTY_PUSH 6 /* n_tty private */
		#define TTY_CLOSING 7 /* ->close() in progress */
		#define TTY_LDISC 9 /* Line discipline attached */
		#define TTY_LDISC_CHANGING 10 /* Line discipline changing */
		#define TTY_HW_COOK_OUT 14 /* Hardware can do output cooking */
		#define TTY_HW_COOK_IN 15 /* Hardware can do input cooking */
		#define TTY_PTY_LOCK 16 /* pty private */