From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Date: Tue, 11 Dec 2018 17:07:43 +0900 From: Sergey Senozhatsky To: Petr Mladek Cc: Feng Tang , Sergey Senozhatsky , Peter Zijlstra , akpm@linux-foundation.org, bp@suse.de, keescook@chromium.org, mm-commits@vger.kernel.org, sergey.senozhatsky@gmail.com, stable@vger.kernel.org, tglx@linutronix.de, Steven Rostedt , Sasha Levin , Andi Kleen , linux-kernel@vger.kernel.org Subject: Re: + panic-avoid-the-extra-noise-dmesg.patch added to -mm tree Message-ID: <20181211080743.GB521@jagdpanzerIV> References: <20181205022654.GA503@jagdpanzerIV> <20181205024713.nqyt6qiamokq7qtl@shbuild888> <20181205025728.GC503@jagdpanzerIV> <20181205052912.GA423@jagdpanzerIV> <20181205080044.GA11190@jagdpanzerIV> <20181205154620.4dqtledc2duhrp2c@shbuild888> <20181206035825.jz2bfh3errj23rjq@shbuild888> <20181207095004.GB3729@jagdpanzerIV> <20181210094554.z5n7dmkrnlcpygg4@shbuild888> <20181210155705.qowbi7xvszzfonzk@pathway.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181210155705.qowbi7xvszzfonzk@pathway.suse.cz> List-ID: On (12/10/18 16:57), Petr Mladek wrote: > > > (masked out) and on panic_cpu disables only SDEI (interrupts from firmware, > > > if I got it right); so it seems that arm64 can handle IRQs after panic. And > > > if there are platforms that handle IRQ (including sysrq) after panic, then > > > both options - making printk a noop or keeping local irqs off - maybe can > > > cause some problems. Or maybe not. We better ask arch people. > > > > Yes, this is very valid concern. And after Petr and you raised it, I did > > some experiments with 3 x86 platforms at my hand, one Apollolake IOT device > > with serial console, one IvyBridge laptop and one Kabylake NUC, the magic key > > all works well before panic, and fails after panic. But I did remember the > > PageUp/PageDown key worked on some laptop years ago. And you actually raised a > > good question: what do we expect for the post-panic kernel? > > I am not sure why it does not work. But it would be nice if sysrq > worked. Absolutely. [..] > I still think that calming down printk() is acceptable when > it can be restored from sysrq. I would agree; peeking one of the two solutions, printk patch is probably preferable. > I think that only few people might be interested into debugging > post-panic problems. We could print a warning for them about > that printk() has got disabled. Dunno. This _maybe_ (speculation!) can upset folks on those platforms that have sysrq working after panic. printk is a common code. I'm probably missing a lot of things here, but just in case, I'm not sure at which point the idea of patching some files under arch/x86 directory was ruled out and why. -ss