85 lines
2.5 KiB
Diff
85 lines
2.5 KiB
Diff
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From jirislaby@gmail.com Thu Nov 25 12:16:42 2010
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From: Jiri Slaby <jslaby@suse.cz>
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Subject: [PATCH 1/1] TTY: don't allow reopen when ldisc is changing
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Date: Thu, 25 Nov 2010 18:16:23 +0100
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There are many WARNINGs like the following reported nowadays:
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WARNING: at drivers/tty/tty_io.c:1331 tty_open+0x2a2/0x49a()
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Hardware name: Latitude E6500
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Modules linked in:
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Pid: 1207, comm: plymouthd Not tainted 2.6.37-rc3-mmotm1123 #3
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Call Trace:
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[<ffffffff8103b189>] warn_slowpath_common+0x80/0x98
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[<ffffffff8103b1b6>] warn_slowpath_null+0x15/0x17
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[<ffffffff8128a3ab>] tty_open+0x2a2/0x49a
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[<ffffffff810fd53f>] chrdev_open+0x11d/0x146
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...
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This means tty_reopen is called without TTY_LDISC set. For further
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considerations, note tty_lock is held in tty_open. TTY_LDISC is cleared in:
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1) __tty_hangup from tty_ldisc_hangup to tty_ldisc_enable. During this
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section tty_lock is held.
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2) tty_release via tty_ldisc_release till the end of tty existence. If
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tty->count <= 1, tty_lock is taken, TTY_CLOSING bit set and then
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tty_ldisc_release called. tty_reopen checks TTY_CLOSING before checking
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TTY_LDISC.
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3) tty_set_ldisc from tty_ldisc_halt to tty_ldisc_enable. We:
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* take tty_lock, set TTY_LDISC_CHANGING, put tty_lock
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* call tty_ldisc_halt (clear TTY_LDISC), tty_lock is _not_ held
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* do some other work
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* take tty_lock, call tty_ldisc_enable (set TTY_LDISC), put
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tty_lock
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So the only option I see is 3). The solution is to check
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TTY_LDISC_CHANGING along with TTY_CLOSING in tty_reopen.
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Nicely reproducible with two processes:
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while (1) {
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fd = open("/dev/ttyS1", O_RDWR);
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if (fd < 0) {
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warn("open");
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continue;
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}
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close(fd);
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}
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--------
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while (1) {
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fd = open("/dev/ttyS1", O_RDWR);
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ld1 = 0; ld2 = 2;
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while (1) {
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ioctl(fd, TIOCSETD, &ld1);
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ioctl(fd, TIOCSETD, &ld2);
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}
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close(fd);
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}
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Signed-off-by: Jiri Slaby <jslaby@suse.cz>
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Reported-by: <Valdis.Kletnieks@vt.edu>
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Cc: Kyle McMartin <kyle@mcmartin.ca>
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Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
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---
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drivers/tty/tty_io.c | 3 ++-
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1 files changed, 2 insertions(+), 1 deletions(-)
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diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
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index c05c5af..878f6d6 100644
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--- a/drivers/char/tty_io.c
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+++ b/drivers/char/tty_io.c
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@@ -1310,7 +1310,8 @@ static int tty_reopen(struct tty_struct *tty)
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{
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struct tty_driver *driver = tty->driver;
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- if (test_bit(TTY_CLOSING, &tty->flags))
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+ if (test_bit(TTY_CLOSING, &tty->flags) ||
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+ test_bit(TTY_LDISC_CHANGING, &tty->flags))
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return -EIO;
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if (driver->type == TTY_DRIVER_TYPE_PTY &&
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--
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1.7.3.1
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