Commit 8f6576ad authored by Alan Cox's avatar Alan Cox Committed by Linus Torvalds
Browse files

tty: fix ldisc lock inversion trace 



This is caused by tty_release using tty_lock_pair to lock both sides of
the pty/tty pair, and then tty_ldisc_release dropping and relocking one
side only.  We can drop both fine, so drop both to avoid any lock
ordering concerns.

Rework the release path to fix the new locking model.

Signed-off-by: default avatarAlan Cox <alan@linux.intel.com>
Acked-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent d3ca8b64

drivers/tty/tty_ldisc.c

+25 −16
Original line number Diff line number Diff line
@@ -894,6 +894,23 @@ int tty_ldisc_setup(struct tty_struct *tty, struct tty_struct *o_tty) 
	tty_ldisc_enable(tty);

	return 0;

}



static void tty_ldisc_kill(struct tty_struct *tty)

{

	mutex_lock(&tty->ldisc_mutex);

	/*

	 * Now kill off the ldisc

	 */

	tty_ldisc_close(tty, tty->ldisc);

	tty_ldisc_put(tty->ldisc);

	/* Force an oops if we mess this up */

	tty->ldisc = NULL;



	/* Ensure the next open requests the N_TTY ldisc */

	tty_set_termios_ldisc(tty, N_TTY);

	mutex_unlock(&tty->ldisc_mutex);

}



/**

 *	tty_ldisc_release		-	release line discipline

 *	@tty: tty being shut down
@@ -912,27 +929,19 @@ void tty_ldisc_release(struct tty_struct *tty, struct tty_struct *o_tty) 
	 * race with the set_ldisc code path.

	 */



	tty_unlock(tty);

	tty_unlock_pair(tty, o_tty);

	tty_ldisc_halt(tty);

	tty_ldisc_flush_works(tty);

	tty_lock(tty);



	mutex_lock(&tty->ldisc_mutex);

	/*

	 * Now kill off the ldisc

	 */

	tty_ldisc_close(tty, tty->ldisc);

	tty_ldisc_put(tty->ldisc);

	/* Force an oops if we mess this up */

	tty->ldisc = NULL;

	if (o_tty) {

		tty_ldisc_halt(o_tty);

		tty_ldisc_flush_works(o_tty);

	}

	tty_lock_pair(tty, o_tty);



	/* Ensure the next open requests the N_TTY ldisc */

	tty_set_termios_ldisc(tty, N_TTY);

	mutex_unlock(&tty->ldisc_mutex);



	/* This will need doing differently if we need to lock */

	tty_ldisc_kill(tty);

	if (o_tty)

		tty_ldisc_release(o_tty, NULL);

		tty_ldisc_kill(o_tty);



	/* And the memory resources remaining (buffers, termios) will be

	   disposed of when the kref hits zero */

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