Jiri Slaby e2efafbf13 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>		2010-11-29 14:52:48 -08:00
..
vt	vcs: make proper usage of the poll flags	2010-11-11 10:51:35 -08:00
Makefile
n_gsm.c	n_gsm: Fix length handling	2010-11-11 11:06:09 -08:00
n_hdlc.c
n_r3964.c
n_tty.c
pty.c
sysrq.c
tty_audit.c
tty_buffer.c	tty: prevent DOS in the flush_to_ldisc	2010-11-09 15:02:02 -08:00
tty_io.c	TTY: don't allow reopen when ldisc is changing	2010-11-29 14:52:48 -08:00
tty_ioctl.c
tty_ldisc.c	TTY: ldisc, fix open flag handling	2010-11-29 14:51:54 -08:00
tty_mutex.c
tty_port.c