linux-kernel - Re: [PATCH v3] mm/oom: do not oom reap task with an unresolved robust futex

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Date:   Wed, 2 Mar 2022 15:24:59 +0100
From:   Michal Hocko <mhocko@...e.com>
To:     Nico Pache <npache@...hat.com>
Cc:     Waiman Long <longman@...hat.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
        jsavitz@...hat.com, peterz@...radead.org, tglx@...utronix.de,
        mingo@...hat.com, dvhart@...radead.org, dave@...olabs.net,
        andrealmeid@...labora.com
Subject: Re: [PATCH v3] mm/oom: do not oom reap task with an unresolved
 robust futex

Sorry, this has slipped through cracks.

On Mon 14-02-22 15:39:31, Nico Pache wrote:
[...]
> We've recently been discussing the following if statement in __oom_reap_task_mm:
> 	if (vma_is_anonymous(vma) || !(vma->vm_flags & VM_SHARED))
> 
> Given the comment above it, and some of the upstream discussion the original
> RFC, we are struggling to see why this should be a `||` and not an `&&`. If we
> only want to reap anon memory and reaping shared memory can be dangerous is this
> statement incorrect?
> 
> We have a patch queued up to make this change, but wanted to get your opinion on
> why this was originally designed this way in case we are missing something.

I do not really see why this would be wrong. Private file backed
mappings can contain a reapable memory as well. I do not see how this
would solve the futex issue.
-- 
Michal Hocko
SUSE Labs