On Sat 2019-04-27 02:16:40, Sergey Senozhatsky wrote: > On (04/27/19 01:43), Sergey Senozhatsky wrote: > [..] > > > The console waiter logic is effective but it does not always > > > work. The current console owner must be calling the console > > > drivers. > > > > > > > Hmm, we might have a bit of a problem here, maybe. > > > > > > Hmm, the printk() might wait forever when NMI stopped > > > the current console owner in the console driver code > > > or with the logbuf_lock taken. > > > > I guess this is why we re-init logbuf lock from panic, > > however, we don't do anything with the console_owner.
> > > The console waiter logic might get solved by clearing > > > the console_owner in console_flush_on_panic(). It can't > > > be much worse, we already ignore console_lock() there, ... > > Hmm, or maybe we are fine... console_waiter logic should work > before we send out stop IPI/NMI from panic CPU. When we call > flush_on_panic() console_unlock() clears console_owner, so > panic_print_sys_info() should not deadlock on console_owner. Good point! > It's probably only problematic if we kill a console_owner > CPU and then try to printk() (from smp_send_stop()) before > we do flush_on_panic()->console_unlock(). Yup. There are called several functions between smp_send_stop() and console_flush_on_panic(). The question is if it is worth a code complication. We could never 100% guarantee that printk() would work in panic(). I more and more understand what Peter Zijlstra means by the duct taping. Best Regards, Petr
