Re: Should mmap MAP_LOCKED fail if mm_poppulate fails?

From: Michal Hocko
Date: Tue Apr 28 2015 - 08:12:21 EST

it seems that the initial email got lost (or ignored). I would like to
revive it again. I've cooked up a potential fix to this issue which will
follow as a reply to this email.

The first patch is dumb and straightforward. It should be safe as is and
also good without the follow up 2 patches which try to handle potential
allocation failures in the do_munmap path more gracefully. As we still
do not fail small allocations even the first patch could be simplified
a bit and the retry loop replaced by a BUG_ON right away. But I felt this
would better be done robust.

An obvious alternative would be patching the man pages to mention the
subtle difference between mlock and MAP_LOCKED semantic. I have checked
debian code search and it shown some applications relying on MAP_LOCKED
but I have no idea whether they really require the mlock all-or-nothing
fault in semantic.

Any thoughts, ideas?

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