Messages in this thread Patch in this message | | | From | Sergey Senozhatsky <> | Date | Sat, 16 Mar 2019 23:40:51 +0900 | Subject | Re: [syzbot? printk?] no WARN_ON() messages printed before "Kernel panic - not syncing: panic_on_warn set ..." |
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On (03/16/19 15:16), Dmitry Vyukov wrote: > > Hmm... sysctl, may be? > > > > > > I figured out that we should restrict it from doing > > > > syslog(SYSLOG_ACTION_CONSOLE_OFF). And I also restricted its access o > > > > /dev/console. But maybe there is something else? It _should_ not be > > > > able to write to random sysctl's. > > > > > > Maybe try running with "ignore_loglevel" kernel command line option added? > > > > Right, that's something I would expect 0-day and syzkaller to do. > > to double-check: enabling this won't lead to verbose/debug level of logging?
My bad, Saturday night.
You are right, this will make it very verbose. May be we can set ignore_loglevel when we set loglevel to CONSOLE_LOGLEVEL_MOTORMOUTH.
Technically, we can have something like this
CPU0 CPU1
foo() panic loglevel_save = console_loglevel .... console_verbose() console_loglevel = ABC .... console_loglevel = loglevel_save smp_send_stop() ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ killed console_flush_on_panic() // console is // NOT verbose
So we either can set ignore_loglevel in console_verbose(). Or call call console_verbose() one more time, once we stopped other CPUs and before we console_flush_on_panic().
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diff --git a/kernel/panic.c b/kernel/panic.c index 0ae0d7332f12..11784d37f625 100644 --- a/kernel/panic.c +++ b/kernel/panic.c @@ -263,6 +263,7 @@ void panic(const char *fmt, ...) if (_crash_kexec_post_notifiers) __crash_kexec(NULL); + console_verbose(); #ifdef CONFIG_VT unblank_screen(); #endif --- But I think that setting ignore_loglevel in console_verbose() is more reliable.
-ss
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