Messages in this thread | | | From | Sergey Senozhatsky <> | Date | Tue, 30 Apr 2019 15:27:51 +0900 | Subject | Re: [PATCH v4] panic: add an option to replay all the printk message in buffer |
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On (04/29/19 13:44), Petr Mladek wrote: > 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.
Agreed.
-ss
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