Commit Graph

14 Commits

Author SHA1 Message Date
Jiri Slaby
0c73c08ec7 TTY: ldisc, wait for ldisc infinitely in hangup
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 <jslaby@suse.cz>
Cc: Dave Young <hidave.darkstar@gmail.com>
Cc: Dave Jones <davej@redhat.com>
Cc: Ben Hutchings <ben@decadent.org.uk>
Cc: Dmitriy Matrosov <sgf.dma@gmail.com>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
2011-11-17 11:36:12 -08:00
Jiri Slaby
300420722e TTY: ldisc, move wait idle to caller
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 <jslaby@suse.cz>
Cc: Dave Young <hidave.darkstar@gmail.com>
Cc: Dave Jones <davej@redhat.com>
Cc: Ben Hutchings <ben@decadent.org.uk>
Cc: Dmitriy Matrosov <sgf.dma@gmail.com>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
2011-11-17 11:36:12 -08:00
Jiri Slaby
df92d0561d TTY: ldisc, allow waiting for ldisc arbitrarily long
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 <jslaby@suse.cz>
Cc: Dave Young <hidave.darkstar@gmail.com>
Cc: Dave Jones <davej@redhat.com>
Cc: Ben Hutchings <ben@decadent.org.uk>
Cc: Dmitriy Matrosov <sgf.dma@gmail.com>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
2011-11-17 11:36:11 -08:00
Jiri Slaby
906cbe1364 TTY: remove tty_locked
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 <jslaby@suse.cz>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Cc: Alan Cox <alan@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
2011-08-23 10:34:07 -07:00
Jiri Slaby
92f6fa09bd TTY: ldisc, do not close until there are readers
We restored tty_ldisc_wait_idle in 100eeae2c5 (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 65b770468e (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
(100eeae2c5), 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 65b770468e 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 <jslaby@suse.cz>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: stable <stable@kernel.org> [32, 33, 34, 39]
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
2011-06-07 10:16:54 -07:00
Jiri Slaby
6716671d8c TTY: introduce deinit helpers for proper ldisc shutdown
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 <jslaby@suse.cz>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: Julian Anastasov <ja@ssi.bg>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
2011-04-19 14:43:01 -07:00
Linus Torvalds
f23eb2b2b2 tty: stop using "delayed_work" in the tty layer
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 <jefdriesen@telenet.be>
Acked-by: Greg KH <gregkh@suse.de>
Acked-by: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2011-03-22 16:17:32 -07:00
Linus Torvalds
f74b944419 Merge branch 'config' of git://git.kernel.org/pub/scm/linux/kernel/git/arnd/bkl
* 'config' of git://git.kernel.org/pub/scm/linux/kernel/git/arnd/bkl:
  BKL: That's all, folks
  fs/locks.c: Remove stale FIXME left over from BKL conversion
  ipx: remove the BKL
  appletalk: remove the BKL
  x25: remove the BKL
  ufs: remove the BKL
  hpfs: remove the BKL
  drivers: remove extraneous includes of smp_lock.h
  tracing: don't trace the BKL
  adfs: remove the big kernel lock
2011-03-16 17:21:00 -07:00
Arnd Bergmann
5edc341313 drivers: remove extraneous includes of smp_lock.h
These were missed the last time I cleaned this up
globally, because of code moving around or new code
getting merged.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
2011-03-02 00:02:40 +01:00
Tejun Heo
0a1f1a0b62 tty_ldisc: don't use flush_scheduled_work()
flush_scheduled_work() is scheduled to be deprecated.  Explicitly sync
flush the used work items instead.  Note that before this change,
flush_scheduled_work() wouldn't have properly flushed tty->buf.work if
it were on timer.

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
2011-02-03 14:12:25 -08:00
Jiri Slaby
7f90cfc505 TTY: ldisc, fix open flag handling
When a concrete ldisc open fails in tty_ldisc_open, we forget to clear
TTY_LDISC_OPEN. This causes a false warning on the next ldisc open:
WARNING: at drivers/char/tty_ldisc.c:445 tty_ldisc_open+0x26/0x38()
Hardware name: System Product Name
Modules linked in: ...
Pid: 5251, comm: a.out Tainted: G        W  2.6.32-5-686 #1
Call Trace:
 [<c1030321>] ? warn_slowpath_common+0x5e/0x8a
 [<c1030357>] ? warn_slowpath_null+0xa/0xc
 [<c119311c>] ? tty_ldisc_open+0x26/0x38
 [<c11936c5>] ? tty_set_ldisc+0x218/0x304
...

So clear the bit when failing...

Introduced in c65c9bc3ef (tty: rewrite the ldisc locking) back in
2.6.31-rc1.

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Cc: Alan Cox <alan@linux.intel.com>
Reported-by: Sergey Lapin <slapin@ossfans.org>
Tested-by: Sergey Lapin <slapin@ossfans.org>
Cc: stable <stable@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
2010-11-29 14:51:54 -08:00
Philippe Rétornaz
1c95ba1e1d tty_ldisc: Fix BUG() on hangup
A kernel BUG when bluetooth rfcomm connection drop while the associated
serial port is open is sometime triggered.

It seems that the line discipline can disappear between the
tty_ldisc_put and tty_ldisc_get. This patch fall back to the N_TTY line
discipline if the previous discipline is not available anymore.

Signed-off-by: Philippe Retornaz <philippe.retornaz@epfl.ch>
Acked-by: Alan Cox <alan@linux.intel.com>
Cc: stable <stable@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
2010-11-09 15:05:50 -08:00
Jiri Slaby
100eeae2c5 TTY: restore tty_ldisc_wait_idle
It was removed in 65b770468e (tty-ldisc: turn ldisc user count into
a proper refcount), but we need to wait for last user to quit the
ldisc before we close it in tty_set_ldisc.

Otherwise weird things start to happen. There might be processes
waiting in tty_read->n_tty_read on tty->read_wait for input to appear
and at that moment, a change of ldisc is fatal. n_tty_close is called,
it frees read_buf and the waiting process is still in the middle of
reading and goes nuts after it is woken.

Previously we prevented close to happen when others are in ldisc ops
by tty_ldisc_wait_idle in tty_set_ldisc. But the commit above removed
that. So revoke the change and test whether there is 1 user (=we), and
allow the close then.

We can do that without ldisc/tty locks, because nobody else can open
the device due to TTY_LDISC_CHANGING bit set, so we in fact wait for
everybody to leave.

I don't understand why tty_ldisc_lock would be needed either when the
counter is an atomic variable, so this is a lockless
tty_ldisc_wait_idle.

On the other hand, if we fail to wait (timeout or signal), we have to
reenable the halted ldiscs, so we take ldisc lock and reuse the setup
path at the end of tty_set_ldisc.

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Tested-by: Sebastian Andrzej Siewior <bigeasy@breakpoint.cc>
LKML-Reference: <20101031104136.GA511@Chamillionaire.breakpoint.cc>
LKML-Reference: <1287669539-22644-1-git-send-email-jslaby@suse.cz>
Cc: Alan Cox <alan@linux.intel.com>
Cc: stable@kernel.org [32, 33, 36]
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
2010-11-09 15:04:21 -08:00
Greg Kroah-Hartman
96fd7ce58f TTY: create drivers/tty and move the tty core files there
The tty code should be in its own subdirectory and not in the char
driver with all of the cruft that is currently there.

Based on work done by Arnd Bergmann <arnd@arndb.de>

Acked-by: Arnd Bergmann <arnd@arndb.de>
Cc: Jiri Slaby <jslaby@suse.cz>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
2010-11-05 08:10:33 -07:00