Re: [PATCH V2,2/2] mm: madvise: skip unmapped vma holes passed to process_madvise

[Andrew Morton <akpm@linux-foundation.org>]

On Tue, 15 Mar 2022 15:58:28 -0700 Minchan Kim <minchan@kernel.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@vger.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?