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tty: reorder ldisc locking

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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>
This commit is contained in:
Arnd Bergmann 2010-06-01 22:53:06 +02:00 committed by Greg Kroah-Hartman
parent be1bc2889a
commit 60af22d2ed
2 changed files with 27 additions and 6 deletions
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9
drivers/char/selection.c
View file

@ -319,8 +319,13 @@ int paste_selection(struct tty_struct *tty)
poke_blanked_console();
release_console_sem();
ld = tty_ldisc_ref_wait(tty);
ld = tty_ldisc_ref(tty);
if (!ld) {
tty_unlock();
ld = tty_ldisc_ref_wait(tty);
tty_lock();
}
add_wait_queue(&vc->paste_wait, &wait);
while (sel_buffer && sel_buffer_lth > pasted) {
set_current_state(TASK_INTERRUPTIBLE);

24
drivers/char/tty_ldisc.c
View file

@ -582,6 +582,7 @@ int tty_set_ldisc(struct tty_struct *tty, int ldisc)
tty_wait_until_sent(tty, 0);
tty_lock();
mutex_lock(&tty->ldisc_mutex);
/*
@ -591,13 +592,13 @@ int tty_set_ldisc(struct tty_struct *tty, int ldisc)
while (test_bit(TTY_LDISC_CHANGING, &tty->flags)) {
mutex_unlock(&tty->ldisc_mutex);
tty_unlock();
wait_event(tty_ldisc_wait,
test_bit(TTY_LDISC_CHANGING, &tty->flags) == 0);
tty_lock();
mutex_lock(&tty->ldisc_mutex);
}
tty_lock();
set_bit(TTY_LDISC_CHANGING, &tty->flags);
/*
@ -634,8 +635,8 @@ int tty_set_ldisc(struct tty_struct *tty, int ldisc)
flush_scheduled_work();
mutex_lock(&tty->ldisc_mutex);
tty_lock();
mutex_lock(&tty->ldisc_mutex);
if (test_bit(TTY_HUPPED, &tty->flags)) {
/* We were raced by the hangup method. It will have stomped
the ldisc data and closed the ldisc down */
@ -782,7 +783,20 @@ void tty_ldisc_hangup(struct tty_struct *tty)
* Avoid racing set_ldisc or tty_ldisc_release
*/
mutex_lock(&tty->ldisc_mutex);
tty_ldisc_halt(tty);
/*
* this is like tty_ldisc_halt, but we need to give up
* the BTM before calling cancel_delayed_work_sync,
* which may need to wait for another function taking the BTM
*/
clear_bit(TTY_LDISC, &tty->flags);
tty_unlock();
cancel_delayed_work_sync(&tty->buf.work);
mutex_unlock(&tty->ldisc_mutex);
tty_lock();
mutex_lock(&tty->ldisc_mutex);
/* At this point we have a closed ldisc and we want to
reopen it. We could defer this to the next open but
it means auditing a lot of other paths so this is
@ -853,8 +867,10 @@ void tty_ldisc_release(struct tty_struct *tty, struct tty_struct *o_tty)
* race with the set_ldisc code path.
*/
tty_unlock();
tty_ldisc_halt(tty);
flush_scheduled_work();
tty_lock();
mutex_lock(&tty->ldisc_mutex);
/*