linux-kernel - Re: [PATCH v2] memcg: allow exiting tasks to write back data to swap

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Message-ID: <7a4e5591f45df455e6a485fc5400989569d3d22d.camel@surriel.com>
Date: Wed, 15 Jan 2025 12:35:37 -0500
From: Rik van Riel <riel@...riel.com>
To: Michal Hocko <mhocko@...e.com>, Johannes Weiner <hannes@...xchg.org>
Cc: Yosry Ahmed <yosryahmed@...gle.com>, Balbir Singh <balbirs@...dia.com>, 
 Roman Gushchin <roman.gushchin@...ux.dev>, hakeel Butt
 <shakeel.butt@...ux.dev>, Muchun Song	 <muchun.song@...ux.dev>, Andrew
 Morton <akpm@...ux-foundation.org>, 	cgroups@...r.kernel.org,
 linux-mm@...ck.org, linux-kernel@...r.kernel.org, 	kernel-team@...a.com,
 Nhat Pham <nphamcs@...il.com>
Subject: Re: [PATCH v2] memcg: allow exiting tasks to write back data to swap

On Tue, 2025-01-14 at 20:42 +0100, Michal Hocko wrote:
> O
> I do agreee that a memory deadlock is not really proper way to deal
> with
> the issue. I have to admit that my understanding was based on ENOMEM
> being properly propagated out of in kernel user page faults. 

It looks like it kind of is.

In case of VM_FAULT_OOM, the page fault code calls
kernelmode_fixup_or_oops(), which a few functions
down calls ex_handler_default(), which advances
regs->ip to the next instruction after the one
that faulted.

Of course, if we have a copy_from_user loop, we
could end up there a bunch of times :)

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