linux-kernel - Re: [PATCH v2] mm: access to uninitialized struct page

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Message-Id: <20180430170145.544342905604331c0e1b95d9@linux-foundation.org>
Date:   Mon, 30 Apr 2018 17:01:45 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Pavel Tatashin <pasha.tatashin@...cle.com>,
        steven.sistare@...cle.com, daniel.m.jordan@...cle.com,
        linux-kernel@...r.kernel.org, tglx@...utronix.de, mhocko@...e.com,
        linux-mm@...ck.org, mgorman@...hsingularity.net, mingo@...nel.org,
        peterz@...radead.org, fengguang.wu@...el.com, dennisszhou@...il.com
Subject: Re: [PATCH v2] mm: access to uninitialized struct page

On Mon, 30 Apr 2018 19:58:58 -0400 Steven Rostedt <rostedt@...dmis.org> wrote:

> On Mon, 30 Apr 2018 16:26:58 -0700
> Andrew Morton <akpm@...ux-foundation.org> wrote:
> 
> > On Thu, 26 Apr 2018 16:26:19 -0400 Pavel Tatashin <pasha.tatashin@...cle.com> wrote:
> > 
> > > The following two bugs were reported by Fengguang Wu:
> > > 
> > > kernel reboot-without-warning in early-boot stage, last printk:
> > > early console in setup code
> > > 
> > > http://lkml.kernel.org/r/20180418135300.inazvpxjxowogyge@wfg-t540p.sh.intel.com
> > > 
> > > ...
> > >
> > > --- a/init/main.c
> > > +++ b/init/main.c
> > > @@ -585,8 +585,8 @@ asmlinkage __visible void __init start_kernel(void)
> > >  	setup_log_buf(0);
> > >  	vfs_caches_init_early();
> > >  	sort_main_extable();
> > > -	trap_init();
> > >  	mm_init();
> > > +	trap_init();
> > >  
> > >  	ftrace_init();  
> > 
> > Gulp.  Let's hope that nothing in mm_init() requires that trap_init()
> > has been run.  What happens if something goes wrong during mm_init()
> > and the architecture attempts to raise a software exception, hits a bus
> > error, div-by-zero, etc, etc?  Might there be hard-to-discover
> > dependencies in such a case?
> 
> I mentioned the same thing.
> 

I guess the same concern applies to all the code which we've always run
before trap_init(), and that's quite a lot of stuff.  So we should be
OK.  But don't quote me ;)