Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754001AbaDDUSY (ORCPT ); Fri, 4 Apr 2014 16:18:24 -0400 Received: from imap.thunk.org ([74.207.234.97]:50129 "EHLO imap.thunk.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753926AbaDDUSX (ORCPT ); Fri, 4 Apr 2014 16:18:23 -0400 Date: Fri, 4 Apr 2014 16:17:50 -0400 From: "Theodore Ts'o" To: Steven Rostedt Cc: Andrew Morton , Linus Torvalds , Andy Lutomirski , Joerg Roedel , Jiri Kosina , Mateusz Guzik , Greg Kroah-Hartman , LKML , Thomas Gleixner , "H. Peter Anvin" , Borislav Petkov , Ingo Molnar , Mel Gorman , Kay Sievers Subject: Re: [RFC PATCH] cmdline: Hide "debug" from /proc/cmdline Message-ID: <20140404201750.GA10275@thunk.org> Mail-Followup-To: Theodore Ts'o , Steven Rostedt , Andrew Morton , Linus Torvalds , Andy Lutomirski , Joerg Roedel , Jiri Kosina , Mateusz Guzik , Greg Kroah-Hartman , LKML , Thomas Gleixner , "H. Peter Anvin" , Borislav Petkov , Ingo Molnar , Mel Gorman , Kay Sievers References:

<20140403104308.GP13491@8bytes.org> <20140403170541.GA19010@thunk.org> <533EF832.1030902@mit.edu> <20140404115139.3ea3d53126094f41bc0579a0@linux-foundation.org> <20140404154426.6f099f7d@gandalf.local.home> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20140404154426.6f099f7d@gandalf.local.home> User-Agent: Mutt/1.5.23 (2014-03-12) X-SA-Exim-Connect-IP: X-SA-Exim-Mail-From: tytso@thunk.org X-SA-Exim-Scanned: No (on imap.thunk.org); SAEximRunCond expanded to false Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Apr 04, 2014 at 03:44:26PM -0400, Steven Rostedt wrote: > I saw one commenter say that this was a kernel bug because writing to > kmsg shouldn't cause the system to hang. > > The rate-limit patch would go along with that idea, and I honestly > think it would be good to rate-limit it in case something else breaks > and starts spamming kmsg. I agree; the only question is what is the appropriate rate limits, which is the question Linus was asking. Personally, I like keeping the current limits (no more than ten messages every 5 seconds) because I don't think dmesg, which is a circular buffer and deliberately kept simple so that printk is guaranteed to work even when things go really bad (and if things do go really bad, there are ways of reading dmesg out from a crash dump, for example, so we want to keep things simple). Peter has argued that it might be cool if the Kernel had a purpose-built in-kernel syslogd sort of interface, that could accept arbitrarily large amounts of data, and presumably it would allocate memory as needed, and since the kernel knows this is log data, if we are under memory pressure, it could release some of the log data, even if the userspace hasn't picked it up yet, under extreme memory pressure. I don't know that it makes sense to do this, since IMHO we can just as easily do this in a user-space process. But I *do* think we should keep the facility used by printk to be as simple and as bulletproof as possible, which means we should really try to keep users of /dev/kmesg to the simple "I'm starting test ", or similar messages. And that argues for using things like the current ratelimit defaults. - Ted -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/