diff options
author | Alan Cox <alan@redhat.com> | 2009-01-02 13:44:56 (GMT) |
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committer | Linus Torvalds <torvalds@linux-foundation.org> | 2009-01-02 18:19:38 (GMT) |
commit | c9b3976e3fec266be25c5001a70aa0a890b6c476 (patch) | |
tree | 6742587ae3193fcfbee2b394aa4f5daca392da17 /drivers/char/tty_ldisc.c | |
parent | d0eafc7db8f170d534a16b5f04617e98ae2025de (diff) | |
download | linux-fsl-qoriq-c9b3976e3fec266be25c5001a70aa0a890b6c476.tar.xz |
tty: Fix PPP hang under load
Signed-off-by: Alan Cox <alan@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'drivers/char/tty_ldisc.c')
-rw-r--r-- | drivers/char/tty_ldisc.c | 30 |
1 files changed, 21 insertions, 9 deletions
diff --git a/drivers/char/tty_ldisc.c b/drivers/char/tty_ldisc.c index f307f13..7a84b40 100644 --- a/drivers/char/tty_ldisc.c +++ b/drivers/char/tty_ldisc.c @@ -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 @@ restart: * 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 @@ restart: * 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 @@ restart: 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); /* |