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authorJiri Slaby <jslaby@suse.cz>2010-11-29 10:16:53 +0100
committerGreg Kroah-Hartman <gregkh@suse.de>2010-11-29 14:52:48 -0800
commite2efafbf139d2bfdfe96f2901f03189fecd172e4 (patch)
tree252ebbb93326f159890b6e1370a909b6ced72c0a /drivers/tty
parent6a20bd45fda271bd57e3ba41b3de3009797f4b5e (diff)
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.c3
1 files changed, 2 insertions, 1 deletions
diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
index c05c5af5aa0..878f6d667b1 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 &&