linux-kernel - Re: [PATCH for 5.8] mm: do_swap_page fix up the error code instantiation

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Date:   Wed, 17 Jun 2020 09:34:30 -0400
From:   Johannes Weiner <hannes@...xchg.org>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Alex Shi <alex.shi@...ux.alibaba.com>,
        Joonsoo Kim <js1304@...il.com>,
        Shakeel Butt <shakeelb@...gle.com>,
        Hugh Dickins <hughd@...gle.com>,
        "Kirill A. Shutemov" <kirill@...temov.name>,
        Roman Gushchin <guro@...com>, linux-mm@...ck.org,
        cgroups@...r.kernel.org, linux-kernel@...r.kernel.org,
        kernel-team@...com
Subject: Re: [PATCH for 5.8] mm: do_swap_page fix up the error code
 instantiation

On Wed, Jun 17, 2020 at 11:02:38AM +0200, Michal Hocko wrote:
> Damn, I forgot to commit my last change (s@err@ret@). Sorry about the
> noise.
> 
> From 50297dd026ebf71fe901e1945a9ce1e8d8aa083b Mon Sep 17 00:00:00 2001
> From: Michal Hocko <mhocko@...e.com>
> Date: Wed, 17 Jun 2020 10:40:47 +0200
> Subject: [PATCH] mm: do_swap_page fix up the error code
> 
> do_swap_page returns error codes from the VM_FAULT* space. try_charge
> might return -ENOMEM, though, and then do_swap_page simply returns 0
> which means a success.
> 
> We almost never return ENOMEM for GFP_KERNEL single page charge. Except
> for async OOM handling (oom_disabled v1). So this needs translation to
> VM_FAULT_OOM otherwise the the page fault path will not notify the
> userspace and wait for an action.
> 
> Fixes: 4c6355b25e8b ("mm: memcontrol: charge swapin pages on instantiation")
> Signed-off-by: Michal Hocko <mhocko@...e.com>

Good catch, thanks Michal.

Acked-by: Johannes Weiner <hannes@...xchg.org>