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    SubjectRe: [PATCH 1/2] TTY: ldisc, fix open flag handling
    On 11/29/2010 10:50 PM, Greg KH wrote:
    > On Thu, Nov 25, 2010 at 12:27:54AM +0100, Jiri Slaby wrote:
    >> 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>
    >
    > Is this still needed, or can I just use your:
    > [PATCH v2 1/2] TTY: don't allow reopen when ldisc is changing
    > patch instead?

    This patch is still needed, it fixes a fail path.

    Other than that there are 3 races in 2.6.36, one of them is introduced
    in 2.6.36, the rest in 2.6.32. For each bug there is a single patch I sent:
    * TTY: open/hangup race fixup
    - introduced in 2.6.36
    - open vs hangup race
    * TTY: don't allow reopen when ldisc is changing
    - tiocsetd vs open race
    * TTY: ldisc, fix open flag handling
    - this you are asking about
    - when ldisc->open fails, we blow up
    * Char: TTY, restore tty_ldisc_wait_idle
    - this is in 37-rc2 already
    - multiple opens followed by tiocsetd blows the machine up

    All of them are stable candidates (but I would give them some time in
    HEAD to see if something breaks, since I opened a can of worms). The
    first one is applicable only to 2.6.36 indeed.

    thanks,
    --
    js
    suse labs


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