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

[Pasi Kärkkäinen]

Hi,

On Thu, Sep 20, 2018 at 10:25:01AM -0400, Mikulas Patocka wrote:
> 
> 
> 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
> > 

Any progress here? Or is more info/stacktrace needed about the hang?


Thanks,

-- Pasi