linux-kernel - Re: [PATCH V2,2/2] mm: madvise: skip unmapped vma holes passed to process

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Message-Id: <20220315164807.7a9cf1694ee2db8709a8597c@linux-foundation.org>
Date:   Tue, 15 Mar 2022 16:48:07 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Minchan Kim <minchan@...nel.org>
Cc:     Charan Teja Kalla <quic_charante@...cinc.com>, surenb@...gle.com,
        vbabka@...e.cz, rientjes@...gle.com, sfr@...b.auug.org.au,
        edgararriaga@...gle.com, nadav.amit@...il.com, mhocko@...e.com,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        "# 5 . 10+" <stable@...r.kernel.org>
Subject: Re: [PATCH V2,2/2] mm: madvise: skip unmapped vma holes passed to
 process_madvise

On Tue, 15 Mar 2022 15:58:28 -0700 Minchan Kim <minchan@...nel.org> wrote:

> On Fri, Mar 11, 2022 at 08:59:06PM +0530, Charan Teja Kalla wrote:
> > The process_madvise() system call is expected to skip holes in vma
> > passed through 'struct iovec' vector list. But do_madvise, which
> > process_madvise() calls for each vma, returns ENOMEM in case of unmapped
> > holes, despite the VMA is processed.
> > Thus process_madvise() should treat ENOMEM as expected and consider the
> > VMA passed to as processed and continue processing other vma's in the
> > vector list. Returning -ENOMEM to user, despite the VMA is processed,
> > will be unable to figure out where to start the next madvise.
> > Fixes: ecb8ac8b1f14("mm/madvise: introduce process_madvise() syscall: an external memory hinting API")
> > Cc: <stable@...r.kernel.org> # 5.10+
> 
> Hmm, not sure whether it's stable material since it changes semantic of
> API. It would be better to change the semantic from 5.19 with man page
> update to specify the change.

It's a very desirable change and it makes the code match the manpage
and it's cc:stable.  I think we should just absorb any transitory
damage which this causes people.  I doubt if there will be much - if
anyone was affected by this they would have already told us that it's
broken?