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tty: reorder ldisc locking
We need to release the BTM in paste_selection() when sleeping in tty_ldisc_ref_wait to avoid deadlocks with tty_ldisc_enable. In tty_set_ldisc, we now always grab the BTM before taking the ldisc_mutex in order to avoid AB-BA deadlocks between the two. tty_ldisc_halt potentially blocks on a workqueue function that takes the BTM, so we must release the BTM before calling it. Signed-off-by: Arnd Bergmann <arnd@arndb.de> Cc: Alan Cox <alan@lxorguk.ukuu.org.uk> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
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@ -319,8 +319,13 @@ int paste_selection(struct tty_struct *tty)
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poke_blanked_console();
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release_console_sem();
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ld = tty_ldisc_ref_wait(tty);
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ld = tty_ldisc_ref(tty);
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if (!ld) {
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tty_unlock();
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ld = tty_ldisc_ref_wait(tty);
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tty_lock();
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}
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add_wait_queue(&vc->paste_wait, &wait);
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while (sel_buffer && sel_buffer_lth > pasted) {
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set_current_state(TASK_INTERRUPTIBLE);
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@ -582,6 +582,7 @@ int tty_set_ldisc(struct tty_struct *tty, int ldisc)
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tty_wait_until_sent(tty, 0);
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tty_lock();
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mutex_lock(&tty->ldisc_mutex);
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/*
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@ -591,13 +592,13 @@ int tty_set_ldisc(struct tty_struct *tty, int ldisc)
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while (test_bit(TTY_LDISC_CHANGING, &tty->flags)) {
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mutex_unlock(&tty->ldisc_mutex);
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tty_unlock();
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wait_event(tty_ldisc_wait,
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test_bit(TTY_LDISC_CHANGING, &tty->flags) == 0);
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tty_lock();
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mutex_lock(&tty->ldisc_mutex);
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}
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tty_lock();
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set_bit(TTY_LDISC_CHANGING, &tty->flags);
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/*
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@ -634,8 +635,8 @@ int tty_set_ldisc(struct tty_struct *tty, int ldisc)
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flush_scheduled_work();
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mutex_lock(&tty->ldisc_mutex);
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tty_lock();
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mutex_lock(&tty->ldisc_mutex);
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if (test_bit(TTY_HUPPED, &tty->flags)) {
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/* We were raced by the hangup method. It will have stomped
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the ldisc data and closed the ldisc down */
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@ -782,7 +783,20 @@ void tty_ldisc_hangup(struct tty_struct *tty)
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* Avoid racing set_ldisc or tty_ldisc_release
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*/
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mutex_lock(&tty->ldisc_mutex);
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tty_ldisc_halt(tty);
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/*
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* this is like tty_ldisc_halt, but we need to give up
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* the BTM before calling cancel_delayed_work_sync,
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* which may need to wait for another function taking the BTM
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*/
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clear_bit(TTY_LDISC, &tty->flags);
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tty_unlock();
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cancel_delayed_work_sync(&tty->buf.work);
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mutex_unlock(&tty->ldisc_mutex);
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tty_lock();
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mutex_lock(&tty->ldisc_mutex);
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/* At this point we have a closed ldisc and we want to
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reopen it. We could defer this to the next open but
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it means auditing a lot of other paths so this is
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@ -853,8 +867,10 @@ void tty_ldisc_release(struct tty_struct *tty, struct tty_struct *o_tty)
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* race with the set_ldisc code path.
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*/
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tty_unlock();
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tty_ldisc_halt(tty);
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flush_scheduled_work();
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tty_lock();
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mutex_lock(&tty->ldisc_mutex);
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/*
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