linux-kernel - Re: [PATCH 01/12] uprobes: split THPs before trying replace them

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Message-Id: <20170124143559.57cea7092a2efff940aeeef0@linux-foundation.org>
Date:   Tue, 24 Jan 2017 14:35:59 -0800
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     "Kirill A. Shutemov" <kirill@...temov.name>
Cc:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Hugh Dickins <hughd@...gle.com>,
        Rik van Riel <riel@...hat.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Oleg Nesterov <oleg@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH 01/12] uprobes: split THPs before trying replace them

On Wed, 25 Jan 2017 01:22:17 +0300 "Kirill A. Shutemov" <kirill@...temov.name> wrote:

> On Tue, Jan 24, 2017 at 01:28:49PM -0800, Andrew Morton wrote:
> > On Tue, 24 Jan 2017 19:28:13 +0300 "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com> wrote:
> > 
> > > For THPs page_check_address() always fails. It's better to split them
> > > first before trying to replace.
> > 
> > So what does this mean.  uprobes simply fails to work when trying to
> > place a probe into a THP memory region?
> 
> Looks like we can end up with endless retry loop in uprobe_write_opcode().
> 
> > How come nobody noticed (and reported) this when using the feature?
> 
> I guess it's not often used for anon memory.

OK,  can we please include discussion of these things in the changelog?