linux-kernel - RE: Removing Mandatory Locks

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Date:   Fri, 20 Aug 2021 08:30:39 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Linus Torvalds' <torvalds@...ux-foundation.org>,
        Jeff Layton <jlayton@...nel.org>
CC:     "Eric W. Biederman" <ebiederm@...ssion.com>,
        Matthew Wilcox <willy@...radead.org>,
        Andy Lutomirski <luto@...nel.org>,
        David Hildenbrand <david@...hat.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        Alexey Dobriyan <adobriyan@...il.com>,
        "Steven Rostedt" <rostedt@...dmis.org>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        "Mark Rutland" <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
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        Huang Ying <ying.huang@...el.com>,
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        Peter Xu <peterx@...hat.com>,
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        Shakeel Butt <shakeelb@...gle.com>,
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        Daniel Jordan <daniel.m.jordan@...cle.com>,
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        Thomas Cedeno <thomascedeno@...gle.com>,
        Collin Fijalkovich <cfijalkovich@...gle.com>,
        Michal Hocko <mhocko@...e.com>,
        Miklos Szeredi <miklos@...redi.hu>,
        Chengguang Xu <cgxu519@...ernel.net>,
        Christian König 
        <ckoenig.leichtzumerken@...il.com>,
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        Linux API <linux-api@...r.kernel.org>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        "<linux-fsdevel@...r.kernel.org>" <linux-fsdevel@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>,
        "Florian Weimer" <fweimer@...hat.com>,
        Michael Kerrisk <mtk.manpages@...il.com>
Subject: RE: Removing Mandatory Locks

From: Linus Torvalds
> Sent: 19 August 2021 23:33
> 
> On Thu, Aug 19, 2021 at 2:43 PM Jeff Layton <jlayton@...nel.org> wrote:
> >
> > What sort of big, ugly warning did you have in mind?
> 
> I originally thought WARN_ON_ONCE() just to get the distro automatic
> error handling involved, but it would probably be a big problem for
> the people who end up having panic-on-warn or something.

Even panic-on-oops is a PITA.
Took us weeks to realise that a customer system that was randomly
rebooting was 'just' having a boring NULL pointer access.
 
> So probably just a "make it a big box" thing that stands out, kind of
> what lockdep etc does with
> 
>         pr_warn("======...====\n");
> 
> around the messages..
> 
> I don't know if distros have some pattern we could use that would end
> up being something that gets reported to the user?

Will users even see it?
A lot of recent distro installs try very hard to hide all the kernel
messages.
OTOH I guess '-o mand' is unlikely to be set on any of those systems.

	David

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