linux-toradex.git/drivers/tty/tty_ldisc.c, branch v3.4.73

Merge 3.2-rc3 into tty-next to handle merge conflict in tty_ldisc.c

2011-11-27T04:07:25+00:00

Signed-off-by: Greg Kroah-Hartman

TTY: ldisc, remove some unneeded includes

2011-11-17T19:44:13+00:00

They were cut&pasted from tty_io. Many of them are not needed in
tty_ldisc.

Signed-off-by: Jiri Slaby 
Cc: Alan Cox 
Signed-off-by: Greg Kroah-Hartman

TTY: ldisc, wait for ldisc infinitely in hangup

2011-11-17T19:36:12+00:00

For /dev/console case, we do not kill all ldisc users. It's due to
redirected_tty_write test in __tty_hangup. In that case there still
might be a process waiting e.g. in n_tty_read for input.

We wait for such processes to disappear. The problem is that we use a
timeout. After this timeout, we continue closing the ldisc and start
freeing tty resources. It obviously leads to crashes when the other
process is woken.

So to fix this, we wait infinitely before reiniting the ldisc. (The
tiocsetd remains untouched -- times out after 5s.)

This is nicely reproducible with this run from shell:
  exec 0<>/dev/console 1<>/dev/console 2<>/dev/console
and stopping a getty like:
  systemctl stop serial-getty@ttyS0.service

The crash proper may be produced only under load or with constified
timing the same as for 92f6fa09b.

Signed-off-by: Jiri Slaby 
Cc: Dave Young 
Cc: Dave Jones 
Cc: Ben Hutchings 
Cc: Dmitriy Matrosov 
Cc: Alan Cox 
Cc: stable 
Signed-off-by: Greg Kroah-Hartman

TTY: ldisc, move wait idle to caller

2011-11-17T19:36:12+00:00

It is the only place where reinit is called from. And we really need
to wait for the old ldisc to go once. Actually this is the place where
the waiting originally was (before removed and re-added later).

This will make the fix in the following patch easier to implement.

Signed-off-by: Jiri Slaby 
Cc: Dave Young 
Cc: Dave Jones 
Cc: Ben Hutchings 
Cc: Dmitriy Matrosov 
Cc: Alan Cox 
Cc: stable 
Signed-off-by: Greg Kroah-Hartman

TTY: ldisc, allow waiting for ldisc arbitrarily long

2011-11-17T19:36:11+00:00

To fix a nasty bug in ldisc hup vs. reinit we need to wait infinitely
long for ldisc to be gone. So here we add a parameter to
tty_ldisc_wait_idle to allow that.

This is only a preparation for the real fix which is done in the
following patches.

Signed-off-by: Jiri Slaby 
Cc: Dave Young 
Cc: Dave Jones 
Cc: Ben Hutchings 
Cc: Dmitriy Matrosov 
Cc: Alan Cox 
Cc: stable 
Signed-off-by: Greg Kroah-Hartman

tty_ldisc: remove unnecessary negative return check for wait_event_timeout

2011-11-15T23:50:30+00:00

wait_event_timeout always return value >= 0
remove the unnecessary ret < 0 check

Signed-off-by: Dave Young 
Acked-by: Jiri Slaby 
Signed-off-by: Greg Kroah-Hartman

TTY: remove tty_locked

2011-08-23T17:34:07+00:00

We used it really only serial and ami_serial. The rest of the
callsites were BUG/WARN_ONs to check if BTM is held. Now that we
pruned tty_locked from both of the real users, we can get rid of
tty_lock along with __big_tty_mutex_owner.

Signed-off-by: Jiri Slaby 
Acked-by: Arnd Bergmann 
Cc: Alan Cox 
Signed-off-by: Greg Kroah-Hartman

TTY: ldisc, do not close until there are readers

2011-06-07T17:16:54+00:00

We restored tty_ldisc_wait_idle in 100eeae2c5c (TTY: restore
tty_ldisc_wait_idle). We used it in the ldisc changing path to fix the
case where there are tasks in n_tty_read waiting for data and somebody
tries to change ldisc.

Similar to the case above, there may be also tasks waiting in
n_tty_read while hangup is performed. As 65b770468e98 (tty-ldisc: turn
ldisc user count into a proper refcount) removed the wait-until-idle
from all paths, hangup path won't wait for them to disappear either
now. So add it back even to the hangup path.

There is a difference, we need uninterruptible sleep as there is
obviously HUP signal pending. So tty_ldisc_wait_idle now sleeps
without possibility to be interrupted. This is what original
tty_ldisc_wait_idle did. After the wait idle reintroduction
(100eeae2c5c), we have had interruptible sleeps for the ldisc changing
path. But as there is a 5s timeout anyway, we don't allow it to be
interrupted from now on. It's not worth the added complexity of
deciding what kind of sleep we want.

Before 65b770468e98 tty_ldisc_release was called also from
tty_ldisc_release. It is called from tty_release, so I don't think we
need to restore that one.

This is nicely reproducible after constifying the timing when
drivers/tty/n_tty.c is patched as follows ("TTY: ntty, add one more
sanity check" patch is needed to actually see it explode):
%% -1548,6 +1549,7 @@ static int n_tty_open(struct tty_struct *tty)

        /* These are ugly. Currently a malloc failure here can panic */
        if (!tty->read_buf) {
+               msleep(100);
                tty->read_buf = kzalloc(N_TTY_BUF_SIZE, GFP_KERNEL);
                if (!tty->read_buf)
                        return -ENOMEM;
%% -1785,6 +1788,7 @@ do_it_again:
                                break;
                        }
                        timeout = schedule_timeout(timeout);
+                       msleep(20);
                        continue;
                }
                __set_current_state(TASK_RUNNING);
===== With a process: =====
    while (1) {
        int fd = open(argv[1], O_RDWR);
        read(fd, buf, sizeof(buf));
        close(fd);
    }
===== and its child: =====
        setsid();
        while (1) {
                int fd = open(tty, O_RDWR|O_NOCTTY);
                ioctl(fd, TIOCSCTTY, 1);
                vhangup();
                close(fd);
                usleep(100 * (10 + random() % 1000));
        }
===== EOF =====

References: https://bugzilla.novell.com/show_bug.cgi?id=693374
References: https://bugzilla.novell.com/show_bug.cgi?id=694509
Signed-off-by: Jiri Slaby 
Cc: Alan Cox 
Cc: Linus Torvalds 
Cc: stable  [32, 33, 34, 39]
Signed-off-by: Greg Kroah-Hartman

TTY: introduce deinit helpers for proper ldisc shutdown

2011-04-19T21:43:01+00:00

Introduce deinitialize_tty_struct which should be called after
initialize_tty_struct and before successfull tty_ldisc_setup.

It calls tty_ldisc_deinit which is opposite of tty_ldisc_init. It only
puts a reference to ldisc and assigns NULL to tty->ldisc.

It will be used to shut down ldisc when tty_release cannot be called
yet.

Signed-off-by: Jiri Slaby 
Cc: Alan Cox 
Cc: Julian Anastasov 
Signed-off-by: Greg Kroah-Hartman

tty: stop using "delayed_work" in the tty layer

2011-03-22T23:17:32+00:00

Using delayed-work for tty flip buffers ends up causing us to wait for
the next tick to complete some actions.  That's usually not all that
noticeable, but for certain latency-critical workloads it ends up being
totally unacceptable.

As an extreme case of this, passing a token back-and-forth over a pty
will take two ticks per iteration, so even just a thousand iterations
will take 8 seconds assuming a common 250Hz configuration.

Avoiding the whole delayed work issue brings that ping-pong test-case
down to 0.009s on my machine.

In more practical terms, this latency has been a performance problem for
things like dive computer simulators (simulating the serial interface
using the ptys) and for other environments (Alan mentions a CP/M emulator).

Reported-by: Jef Driesen 
Acked-by: Greg KH 
Acked-by: Alan Cox 
Signed-off-by: Linus Torvalds