linux-kernel - Re: [PATCH] mm: mlockall error for flag MCL

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Date:   Mon, 27 May 2019 09:04:15 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Daniel Jordan <daniel.m.jordan@...cle.com>
Cc:     "Potyra, Stefan" <Stefan.Potyra@...ktrobit.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Jordan, Tobias" <Tobias.Jordan@...ktrobit.com>,
        akpm@...ux-foundation.org, vbabka@...e.cz,
        kirill.shutemov@...ux.intel.com, linux-api@...r.kernel.org
Subject: Re: [PATCH] mm: mlockall error for flag MCL_ONFAULT

On Fri 24-05-19 17:43:04, Daniel Jordan wrote:
> [ 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@...cle.com>
> 
> [1] https://sources.debian.org/src/stress-ng/0.09.50-1/stress-mlock.c/?hl=203#L203

Well spotted and the fix looks reasonable as well. Quoting the man page
seems useful as well.

Acked-by: Michal Hocko <mhocko@...e.com>

Thanks!
-- 
Michal Hocko
SUSE Labs