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

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?

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.