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| author | Jiri Slaby <jslaby@suse.cz> | 2010-11-29 12:16:53 +0300 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@suse.de> | 2010-11-30 01:52:48 +0300 |
| commit | e2efafbf139d2bfdfe96f2901f03189fecd172e4 (patch) | |
| tree | 252ebbb93326f159890b6e1370a909b6ced72c0a /drivers/tty | |
| parent | 6a20bd45fda271bd57e3ba41b3de3009797f4b5e (diff) | |
| download | linux-e2efafbf139d2bfdfe96f2901f03189fecd172e4.tar.xz | |
TTY: don't allow reopen when ldisc is changing
There are many WARNINGs like the following reported nowadays:
WARNING: at drivers/tty/tty_io.c:1331 tty_open+0x2a2/0x49a()
Hardware name: Latitude E6500
Modules linked in:
Pid: 1207, comm: plymouthd Not tainted 2.6.37-rc3-mmotm1123 #3
Call Trace:
[<ffffffff8103b189>] warn_slowpath_common+0x80/0x98
[<ffffffff8103b1b6>] warn_slowpath_null+0x15/0x17
[<ffffffff8128a3ab>] tty_open+0x2a2/0x49a
[<ffffffff810fd53f>] chrdev_open+0x11d/0x146
...
This means tty_reopen is called without TTY_LDISC set. For further
considerations, note tty_lock is held in tty_open. TTY_LDISC is cleared in:
1) __tty_hangup from tty_ldisc_hangup to tty_ldisc_enable. During this
section tty_lock is held. However tty_lock is temporarily dropped in
the middle of the function by tty_ldisc_hangup.
2) tty_release via tty_ldisc_release till the end of tty existence. If
tty->count <= 1, tty_lock is taken, TTY_CLOSING bit set and then
tty_ldisc_release called. tty_reopen checks TTY_CLOSING before checking
TTY_LDISC.
3) tty_set_ldisc from tty_ldisc_halt to tty_ldisc_enable. We:
* take tty_lock, set TTY_LDISC_CHANGING, put tty_lock
* call tty_ldisc_halt (clear TTY_LDISC), tty_lock is _not_ held
* do some other work
* take tty_lock, call tty_ldisc_enable (set TTY_LDISC), put
tty_lock
I cannot see how 2) can be a problem, as there I see no race. OTOH, 1)
and 3) can happen without problems. This patch the case 3) by checking
TTY_LDISC_CHANGING along with TTY_CLOSING in tty_reopen. 1) will be
fixed in the following patch.
Nicely reproducible with two processes:
while (1) {
fd = open("/dev/ttyS1", O_RDWR);
if (fd < 0) {
warn("open");
continue;
}
close(fd);
}
--------
while (1) {
fd = open("/dev/ttyS1", O_RDWR);
ld1 = 0; ld2 = 2;
while (1) {
ioctl(fd, TIOCSETD, &ld1);
ioctl(fd, TIOCSETD, &ld2);
}
close(fd);
}
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Reported-by: <Valdis.Kletnieks@vt.edu>
Cc: Kyle McMartin <kyle@mcmartin.ca>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: stable <stable@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Diffstat (limited to 'drivers/tty')
| -rw-r--r-- | drivers/tty/tty_io.c | 3 |
1 files changed, 2 insertions, 1 deletions
diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c index c05c5af5aa04..878f6d667b17 100644 --- a/drivers/tty/tty_io.c +++ b/drivers/tty/tty_io.c @@ -1310,7 +1310,8 @@ static int tty_reopen(struct tty_struct *tty) { struct tty_driver *driver = tty->driver; - if (test_bit(TTY_CLOSING, &tty->flags)) + if (test_bit(TTY_CLOSING, &tty->flags) || + test_bit(TTY_LDISC_CHANGING, &tty->flags)) return -EIO; if (driver->type == TTY_DRIVER_TYPE_PTY && |