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    SubjectRe: [043/127] TTY: ldisc, fix open flag handling
    On 12/08/2010 04:02 PM, Greg KH wrote:
    > On Wed, Dec 08, 2010 at 07:24:46AM +0100, Jiri Slaby wrote:
    >> On 12/08/2010 01:43 AM, Greg KH wrote:
    >>> 2.6.32-stable review patch. If anyone has any objections, please let us know.
    >>>
    >>> ------------------
    >>>
    >>> From: Jiri Slaby <jslaby@suse.cz>
    >>>
    >>> commit 7f90cfc505d613f4faf096e0d84ffe99208057d9 upstream.
    >>>
    >>> 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 c65c9bc3efa (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>
    >>> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
    >>>
    >>> ---
    >>> drivers/char/tty_ldisc.c | 9 +++++++--
    >>> 1 file changed, 7 insertions(+), 2 deletions(-)
    >>>
    >>> --- a/drivers/char/tty_ldisc.c
    >>> +++ b/drivers/char/tty_ldisc.c
    >>> @@ -444,9 +444,14 @@ static void tty_set_termios_ldisc(struct
    >>>
    >>> static int tty_ldisc_open(struct tty_struct *tty, struct tty_ldisc *ld)
    >>> {
    >>> + int ret;
    >>> +
    >>> WARN_ON(test_and_set_bit(TTY_LDISC_OPEN, &tty->flags));
    >>> - if (ld->ops->open)
    >>> - return ld->ops->open(tty);
    >>> + if (ld->ops->open) {
    >>> + ret = ld->ops->open(tty);
    >>> + if (ret)
    >>> + clear_bit(TTY_LDISC_OPEN, &tty->flags);
    >>> + }
    >>> return 0;
    >>
    >> Whoops, this should write return ret; (with int ret = 0;)
    >>
    >> Do you want me to send the patch against rebased on .32?
    >
    > No, send it based on Linus's tree as it's wrong there, right? Then it
    > will move through to the stable kernels.

    Nope, in 2.6.36 and newer it looks differently, only the .32 backport is
    broken.

    The .36 backport is OK:
    --- a/drivers/char/tty_ldisc.c
    +++ b/drivers/char/tty_ldisc.c
    @@ -454,6 +454,8 @@ static int tty_ldisc_open(struct tty_str
    /* BTM here locks versus a hangup event */
    WARN_ON(!tty_locked());
    ret = ld->ops->open(tty);
    + if (ret)
    + clear_bit(TTY_LDISC_OPEN, &tty->flags);
    return ret;
    }
    return 0;
    thanks,
    --
    js
    suse labs


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