Re: [PATCH] mm: mlockall error for flag MCL_ONFAULT

[ Adding linux-api and some of the people who were involved in the
MCL_ONFAULT/mlock2/etc discussions.  Author of the Fixes patch appears to
have moved on. ]

On Wed, May 22, 2019 at 11:23:37AM +0000, Potyra, Stefan wrote:

If mlockall() is called with only MCL_ONFAULT as flag,
it removes any previously applied lockings and does
nothing else.

The change looks reasonable.  Hard to imagine any application relies on it, and
they really shouldn't be if they are.  Debian codesearch turned up only a few
cases where stress-ng was doing this for unknown reasons[1] and this change
isn't gonna break those.  In this case I think changing the syscall's behavior
is justified.  

This behavior is counter-intuitive and doesn't match the
Linux man page.

I'd quote it for the changelog:

  For mlockall():

  EINVAL Unknown  flags were specified or MCL_ONFAULT was specified with‐
         out either MCL_FUTURE or MCL_CURRENT.

With that you can add

Reviewed-by: Daniel Jordan <daniel.m.jordan@oracle.com>

[1] https://sources.debian.org/src/stress-ng/0.09.50-1/stress-mlock.c/?hl=203#L203