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    SubjectRe: [PATCHv5 0/7] tty: Hold write ldisc sem in tty_reopen()


    On Tue, 18 Sep 2018, Dmitry Safonov wrote:

    > Hi all,
    >
    > Three fixes that worth to have in the @stable, as they were hit by
    > different people, including Arista on v4.9 stable.
    >
    > And for linux-next - adding lockdep asserts for line discipline changing
    > code, verifying that write ldisc sem will be held forthwith.
    >
    > The last patch is an optional and probably, timeout can be dropped for
    > read_lock(). I'll do it if everyone agrees.
    > (Or as per discussion with Peter in v3, just convert ldisc to
    > a regular rwsem).
    >
    > Thanks,
    > Dima

    I confirm that this patch series fixes the crash for me.

    Tested-by: Mikulas Patocka <mpatocka@redhat.com>


    > Changes since v4:
    > - back to lock ldisc with (5*HZ) timeout in tty_reopen()
    > (LKP report link: lkml.kernel.org/r/<1536940609.3185.29.camel@arista.com>)
    > - reordered 3/7 with 2/7 for LKP robot
    >
    > Changes since v3:
    > - Added tested-by Mark Rutland (thanks!)
    > - Dropped patch with smp_wmb() - wrong idea
    > - lockdep_assert_held() should be actually lockdep_assert_held_exclusive()
    > - Described why tty_ldisc_open() can be called without ldisc_sem held
    > for pty slave end (o_tty).
    > - Added Peter's patch for dropping self-made lockdep annotations
    > - Fix for a reader(s) of ldisc semaphore waiting for an active reader(s)
    >
    > Changes since v2:
    > - Added reviewed-by tags
    > - Hopefully, fixed reported by 0-day issue.
    > - Added optional fix for wait_readers decrement
    >
    > Changes since v1:
    > - Added tested-by/reported-by tags
    > - Dropped 3/4 (locking tty pair for lockdep sake),
    > Because of that - not adding lockdep_assert_held() in tty_ldisc_open()
    > - Added 4/4 cleanup to inc tty->count only on success of
    > tty_ldisc_reinit()
    > - lock ldisc without (5*HZ) timeout in tty_reopen()
    >
    > v1 link: lkml.kernel.org/r/<20180829022353.23568-1-dima@arista.com>
    > v2 link: lkml.kernel.org/r/<20180903165257.29227-1-dima@arista.com>
    > v3 link: lkml.kernel.org/r/<20180911014821.26286-1-dima@arista.com>
    > v4 link: lkml.kernel.org/r/<20180912001702.18522-1-dima@arista.com>
    >
    > Cc: Daniel Axtens <dja@axtens.net>
    > Cc: Dmitry Vyukov <dvyukov@google.com>
    > Cc: Mark Rutland <mark.rutland@arm.com>
    > Cc: Michael Neuling <mikey@neuling.org>
    > Cc: Mikulas Patocka <mpatocka@redhat.com>
    > Cc: Nathan March <nathan@gt.net>
    > Cc: Pasi Kärkkäinen <pasik@iki.fi>
    > Cc: Peter Hurley <peter@hurleysoftware.com>
    > Cc: Peter Zijlstra <peterz@infradead.org>
    > Cc: "Rong, Chen" <rong.a.chen@intel.com>
    > Cc: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
    > Cc: Tan Xiaojun <tanxiaojun@huawei.com>
    > Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
    > (please, ignore if I Cc'ed you mistakenly)
    >
    > Dmitry Safonov (6):
    > tty: Drop tty->count on tty_reopen() failure
    > tty/ldsem: Wake up readers after timed out down_write()
    > tty: Hold tty_ldisc_lock() during tty_reopen()
    > tty: Simplify tty->count math in tty_reopen()
    > tty/ldsem: Add lockdep asserts for ldisc_sem
    > tty/ldsem: Decrement wait_readers on timeouted down_read()
    >
    > Peter Zijlstra (1):
    > tty/ldsem: Convert to regular lockdep annotations
    >
    > drivers/tty/tty_io.c | 13 ++++++++---
    > drivers/tty/tty_ldisc.c | 9 +++++++
    > drivers/tty/tty_ldsem.c | 62 ++++++++++++++++++++-----------------------------
    > 3 files changed, 44 insertions(+), 40 deletions(-)
    >
    > --
    > 2.13.6
    >
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