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


    On Wed, 19 Sep 2018, Dmitry Safonov wrote:

    > On Wed, 2018-09-19 at 16:03 -0400, Mikulas Patocka wrote:
    > >
    > > On Wed, 19 Sep 2018, Dmitry Safonov wrote:
    > > > Thanks much for the testing, Mikulas.
    > > > Could you try to bisect which of the patches causes it?
    > > > The most important are 1,2,3 - probably, one of them caused it..
    > > > I'll stare a bit into the code.
    > >
    > > The patch 3 causes it.
    > >
    > > The hangs during reboot take either 80 seconds, 3 minutes or 3:25.
    >
    > Thanks much for that again.
    > Any chance you have sysrq enabled and could print: locks held in system
    > and kernel backtraces for applications?

    Stacktrace doesn't work on parisc. It used to work on 4.18, but the kernel
    4.19 reportedly requires patched binutils.

    Mikulas

    > I suppose, userspace hangs in n_tty_receive_buf_common(), which is
    > better of cause than null-ptr dereference, but I believe we can improve
    > it by stopping a reader earlier if there is any writer pending.
    >
    > --
    > Thanks,
    > Dmitry
    >

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