linux-kernel - Re: [PATCH v2] mm: mlockall error for flag MCL

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Message-ID: <7d5b948d-0253-e73e-980f-f6db5f92b461@suse.cz>
Date:   Mon, 27 May 2019 15:19:44 +0200
From:   Vlastimil Babka <vbabka@...e.cz>
To:     "Potyra, Stefan" <Stefan.Potyra@...ktrobit.com>,
        Michal Hocko <mhocko@...nel.org>,
        Daniel Jordan <daniel.m.jordan@...cle.com>
Cc:     "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" <akpm@...ux-foundation.org>,
        "kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com>,
        "linux-api@...r.kernel.org" <linux-api@...r.kernel.org>
Subject: Re: [PATCH v2] mm: mlockall error for flag MCL_ONFAULT

On 5/27/19 9:53 AM, Potyra, Stefan wrote:
> If mlockall() is called with only MCL_ONFAULT as flag,
> it removes any previously applied lockings and does
> nothing else.
> 
> This behavior is counter-intuitive and doesn't match the
> Linux man page.
> 
>   For mlockall():
> 
>   EINVAL Unknown  flags were specified or MCL_ONFAULT was specified with‐
>          out either MCL_FUTURE or MCL_CURRENT.
> 
> Consequently, return the error EINVAL, if only MCL_ONFAULT
> is passed. That way, applications will at least detect that
> they are calling mlockall() incorrectly.
> 
> Fixes: b0f205c2a308 ("mm: mlock: add mlock flags to enable VM_LOCKONFAULT usage")
> Signed-off-by: Stefan Potyra <Stefan.Potyra@...ktrobit.com>
> Reviewed-by: Daniel Jordan <daniel.m.jordan@...cle.com>
> Acked-by: Michal Hocko <mhocko@...e.com>

Acked-by: Vlastimil Babka <vbabka@...e.cz>

Thanks, shame we didn't catch it during review. Hope nobody will report
a regression.

> ---
>  mm/mlock.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/mlock.c b/mm/mlock.c
> index e492a155c51a..03f39cbdd4c4 100644
> --- a/mm/mlock.c
> +++ b/mm/mlock.c
> @@ -797,7 +797,8 @@ SYSCALL_DEFINE1(mlockall, int, flags)
>  	unsigned long lock_limit;
>  	int ret;
>  
> -	if (!flags || (flags & ~(MCL_CURRENT | MCL_FUTURE | MCL_ONFAULT)))
> +	if (!flags || (flags & ~(MCL_CURRENT | MCL_FUTURE | MCL_ONFAULT)) ||
> +	    flags == MCL_ONFAULT)
>  		return -EINVAL;
>  
>  	if (!can_do_mlock())
>