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

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Message-ID: <20170124225625.GD19920@node.shutemov.name>
Date:   Wed, 25 Jan 2017 01:56:25 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     Andrew Morton <akpm@...ux-foundation.org>
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 Tue, Jan 24, 2017 at 02:35:59PM -0800, Andrew Morton wrote:
> 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?

Okay, I'll try to come up with a test case too.

-- 
 Kirill A. Shutemov