linux-kernel - Re: WARNING: at mm/mremap.c:211 move_page

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Message-ID: <20200713121245.GA3926869@google.com>
Date:   Mon, 13 Jul 2020 08:12:45 -0400
From:   Joel Fernandes <joel@...lfernandes.org>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Naresh Kamboju <naresh.kamboju@...aro.org>,
        linux- stable <stable@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>,
        linux-mm <linux-mm@...ck.org>, Arnd Bergmann <arnd@...db.de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Roman Gushchin <guro@...com>, Michal Hocko <mhocko@...nel.org>,
        lkft-triage@...ts.linaro.org, Chris Down <chris@...isdown.name>,
        Michel Lespinasse <walken@...gle.com>,
        Fan Yang <Fan_Yang@...u.edu.cn>,
        Brian Geffon <bgeffon@...gle.com>,
        Anshuman Khandual <anshuman.khandual@....com>,
        Will Deacon <will@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>, pugaowei@...il.com,
        Jerome Glisse <jglisse@...hat.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Hugh Dickins <hughd@...gle.com>,
        Al Viro <viro@...iv.linux.org.uk>, Tejun Heo <tj@...nel.org>,
        Sasha Levin <sashal@...nel.org>
Subject: Re: WARNING: at mm/mremap.c:211 move_page_tables in i386

On Sun, Jul 12, 2020 at 08:51:26PM -0700, Linus Torvalds wrote:
> > > Maybe saying "doing the pmd copies for the initial stack isn't
> > > important, so let's just note this as a special case and get rid of
> > > the WARN_ON()" might be an alternative solution.
> >
> > Personally, I feel it is better to keep the warning just so in the future we
> > can detect any bugs.
> 
> I don't disagree, the warning didn't happen to find a bug now, but it
> did fine a case we might be able to do better.
> 
> So now that I feel we understand the issue, and it's not a horrible
> problem, just a (very hard to trigger) warning, I don't think there's
> any huge hurry.
> 
> I think think I will - for now - change the WARN_ON() to
> WARN_ON_ONCE() (so that it doesn't floow the logs if somebody triggers
> this odd special case  this malisiously), and add a note about how
> this happens to the code for posterito.
> 
> And if/when you figure out a better way to fix it, we can update the note.
> 
> Ok?

Yes, that sounds great to me.

thanks,

 - Joel