On Sat, Dec 08, 2018 at 12:12:49PM +0900, Sergey Senozhatsky wrote: > On (10/16/18 14:04), Sergey Senozhatsky wrote: > [..] > > - The first entry point is console ->write() callback, which we call > > from printk(). A possible deadlock scenario there is: > > > > CPU0 > > <NMI> > > spin_lock_irqsave(&port->lock, flags) << deadlock > > serial_foo_write() > > call_console_drivers() > > console_unlock() > > console_flush_on_panic() > > panic() > > <NMI/> > > spin_lock_irqsave(&port->lock, flags) > > serial_foo_write() > > call_console_drivers() > > console_unlock() > > printk() > > ... > > [..] > > - The rest (of entry points) requires a bit different handling. > > Let's take a look at the following backtrace: > > > > CPU0 > > <IRQ> > > spin_lock_irqsave(&port->lock, flags) << deadlock > > serial_foo_write() > > call_console_drivers() > > console_unlock() > > printk() > > __queue_work() > > tty_flip_buffer_push() > > spin_lock_irqsave(&port->lock, flags) > > serial_foo_handle_IRQ() > > <IRQ/> > > > > Serial drivers invoke tons of core kernel functions - WQ, MM, etc. All > > of which may printk() in various cases. So we can't really just > > "remove those printk-s". The simples way to address this seems to be > > PRINTK_SAFE_CONTEXT_MASK. > > serial/UART and printk guys, sorry to bother you, do you hate this > idea of removing console_driver->CORE KERNEL->printk->console_driver > deadlock path? Or is there any chance we can move forward? If done in a sane manner, no objection from me.
