On Mon 2019-09-23 19:21:00, Sergey Senozhatsky wrote: > So we have > > port->lock -> MM -> zone->lock > // from pty_write()->__tty_buffer_request_room()->kmalloc() > > vs > > zone->lock -> printk() -> port->lock > // from __offline_pages()->__offline_isolated_pages()->printk() If I understand it correctly then this is the re-appearing problem. The only systematic solution with the current approach is to take port->lock in printk_safe/printk_deferred context. But this is a massive change that almost nobody wants. Instead, we want the changes that were discussed on Plumbers. Now, the question is what to do with existing kernels. There were several lockdep reports. And I am a bit lost. Did anyone seen real deadlocks or just the lockdep reports? To be clear. I would feel more comfortable when there are no deadlocks. But I also do not want to invest too much time into old kernels. All these problems were there for ages. We could finally see them because lockdep was enabled in printk() thanks to printk_safe. Well, it is getting worse over time with the increasing complexity and number of debugging messages. > A number of debugging options make the kernel less stable. > Sad but true. Yeah. The only good thing is that most debug options are not enabled on production systems. It is not an excuse for ignoring the problems. But it might be important for prioritizing. Best Regards, Petr
