From mboxrd@z Thu Jan 1 00:00:00 1970 From: Sergey Senozhatsky Subject: Re: [RFC][PATCHv2 1/4] panic: avoid deadlocks in re-entrant console drivers Date: Tue, 23 Oct 2018 21:04:41 +0900 Message-ID: <20181023120441.GB10251@jagdpanzerIV> References: <20181016050428.17966-1-sergey.senozhatsky@gmail.com> <20181016050428.17966-2-sergey.senozhatsky@gmail.com> <20181023110751.un2u67bc7dpo4ska@pathway.suse.cz> <20181023115433.GA10251@jagdpanzerIV> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20181023115433.GA10251@jagdpanzerIV> Sender: linux-kernel-owner@vger.kernel.org To: Petr Mladek Cc: linux-kernel@vger.kernel.org, Steven Rostedt , Daniel Wang , Peter Zijlstra , Andrew Morton , Linus Torvalds , Greg Kroah-Hartman , Alan Cox , Jiri Slaby , Peter Feiner , linux-serial@vger.kernel.org, Sergey Senozhatsky , Sergey Senozhatsky List-Id: linux-serial@vger.kernel.org On (10/23/18 20:54), Sergey Senozhatsky wrote: > So I did look at what lib/bust_spinlocks.c does; and I agree that waking > up klogd makes little sense, on the other hand it just sets per-cpu > pending bit, so not a big deal. console_unlock() should do there the > same thing as console_flush_on_panic(). Yes. However, a bit of a bigger > argument: > __attribute__((weak)) suggests that bust_spinlocks() is arch-dependent > and it's up to arch to do some extra stuff there [if needed]. So that's > why I decided to keep bust_spinlocks(0) in panic() and, thus, call into > arch-specific code (or common bust_spinlocks); then bump oops_in_progress > so serial consoles become re-entrant and finally call > console_flush_on_panic(). Seems that s390 is the only arch which defines its own bust_spinlocks(). Not sure why... Just to play games with console_loglevel? --- void bust_spinlocks(int yes) { if (yes) { oops_in_progress = 1; } else { int loglevel_save = console_loglevel; console_unblank(); oops_in_progress = 0; /* * OK, the message is on the console. Now we call printk() * without oops_in_progress set so that printk will give klogd * a poke. Hold onto your hats... */ console_loglevel = 15; printk(" "); console_loglevel = loglevel_save; } } --- The "printk(" "); without oops_in_progress" part is a bit worrisome. This thing technically can deadlock. Unless s390 has no NMI panic(). -ss