Date: Fri, 1 Oct 2021 14:09:55 +0200 From: Petr Mladek <pmladek@...e.com> To: Steven Rostedt <rostedt@...dmis.org> Cc: "Paul E. McKenney" <paulmck@...nel.org>, Alexander Popov <alex.popov@...ux.com>, Jonathan Corbet <corbet@....net>, Andrew Morton <akpm@...ux-foundation.org>, Thomas Gleixner <tglx@...utronix.de>, Peter Zijlstra <peterz@...radead.org>, Joerg Roedel <jroedel@...e.de>, Maciej Rozycki <macro@...am.me.uk>, Muchun Song <songmuchun@...edance.com>, Viresh Kumar <viresh.kumar@...aro.org>, Robin Murphy <robin.murphy@....com>, Randy Dunlap <rdunlap@...radead.org>, Lu Baolu <baolu.lu@...ux.intel.com>, Kees Cook <keescook@...omium.org>, Luis Chamberlain <mcgrof@...nel.org>, Wei Liu <wl@....org>, John Ogness <john.ogness@...utronix.de>, Andy Shevchenko <andriy.shevchenko@...ux.intel.com>, Alexey Kardashevskiy <aik@...abs.ru>, Christophe Leroy <christophe.leroy@...roup.eu>, Jann Horn <jannh@...gle.com>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Mark Rutland <mark.rutland@....com>, Andy Lutomirski <luto@...nel.org>, Dave Hansen <dave.hansen@...ux.intel.com>, Thomas Garnier <thgarnie@...gle.com>, Will Deacon <will.deacon@....com>, Ard Biesheuvel <ard.biesheuvel@...aro.org>, Laura Abbott <labbott@...hat.com>, David S Miller <davem@...emloft.net>, Borislav Petkov <bp@...en8.de>, kernel-hardening@...ts.openwall.com, linux-hardening@...r.kernel.org, linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org, notify@...nel.org, Linus Torvalds <torvalds@...ux-foundation.org> Subject: Re: [PATCH] Introduce the pkill_on_warn boot parameter On Thu 2021-09-30 12:59:03, Steven Rostedt wrote: > On Thu, 30 Sep 2021 11:15:41 +0200 > Petr Mladek <pmladek@...e.com> wrote: > > > On Wed 2021-09-29 12:49:24, Paul E. McKenney wrote: > > > On Wed, Sep 29, 2021 at 10:01:33PM +0300, Alexander Popov wrote: > > > > On 29.09.2021 21:58, Alexander Popov wrote: > > > > > Currently, the Linux kernel provides two types of reaction to kernel > > > > > warnings: > > > > > 1. Do nothing (by default), > > > > > 2. Call panic() if panic_on_warn is set. That's a very strong reaction, > > > > > so panic_on_warn is usually disabled on production systems. > > > > Honestly, I am not sure if panic_on_warn() or the new pkill_on_warn() > > work as expected. I wonder who uses it in practice and what is > > the experience. > > Several people use it, as I see reports all the time when someone can > trigger a warn on from user space, and it's listed as a DOS of the > system. Good to know. > > The problem is that many developers do not know about this behavior. > > They use WARN() when they are lazy to write more useful message or when > > they want to see all the provided details: task, registry, backtrace. > > WARN() Should never be used just because of laziness. If it is, then > that's a bug. Let's not use that as an excuse to shoot down this > proposal. WARN() should only be used to test assumptions where you do > not believe something can happen. I use it all the time when the logic > prevents some state, and have the WARN() enabled if that state is hit. > Because to me, it shows something that shouldn't happen happened, and I > need to fix the code. I have just double checked code written or reviewed by me and it mostly follow the rules. But it is partly just by chance. I did not have these rather clear rules in my head. But for example, the following older WARN() in format_decode() in lib/vsprintf.c is questionable: WARN_ONCE(1, "Please remove unsupported %%%c in format string\n", *fmt); I guess that the WARN() was used to easily locate the caller. But it is not a reason the reboot the system or kill the process, definitely. Maybe, we could implement an alternative macro for these situations, e.g. DEBUG() or warn(). > > Well, this might be different. Developers might learn this the hard > > way from bug reports. But there will be bug reports only when > > anyone really enables this behavior. They will enable it only > > when it works the right way most of the time. > > The panic_on_warn() has been used for years now. I do not think this is > an issue. If panic_on_warn() is widely used then pkill_on_warn() is fine as well. Best Regards, Petr
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