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

[Dmitry Safonov <dima@arista.com>]

On Wed, 2018-09-19 at 13:35 -0400, Mikulas Patocka wrote:
> 
> On Wed, 19 Sep 2018, Mikulas Patocka wrote:
> 
> > 
> > 
> > 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>
> 
> I was too quick to acknowledge this patchset. It doesn't work.
> 
> This patchset fixes the crash, but it introduces another bug - when I
> type 
> 'reboot' on the console, it prints 'INIT: Switching to runlevel: 6'
> and 
> then it gets stuck for 80 seconds before proceeding with the reboot.
> When 
> I revert this patchset 'reboot' reboots the machine without any
> delay. 
> This bug was reproduced on Debian 5 userspace on pa-risc.

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.

-- 
Thanks,
             Dmitry