linux-kernel - memcg && uaccess (Was: [PATCH 1/2] kernel/fork: handle put_user errors for CLONE_CHILD

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Message-ID: <20150206203246.GA16924@redhat.com>
Date:	Fri, 6 Feb 2015 21:32:46 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Konstantin Khlebnikov <khlebnikov@...dex-team.ru>,
	Johannes Weiner <hannes@...xchg.org>,
	Michal Hocko <mhocko@...e.cz>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	linux-api@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org,
	Roman Gushchin <klamm@...dex-team.ru>,
	Nikita Vetoshkin <nekto0n@...dex-team.ru>,
	Pavel Emelyanov <xemul@...allels.com>
Subject: memcg && uaccess (Was: [PATCH 1/2] kernel/fork: handle put_user
	errors for CLONE_CHILD_SETTID/CLEARTID)

Add cc's.

On 02/06, Oleg Nesterov wrote:
>
> And in fact I think that this is not set_child_tid/etc-specific. Perhaps
> I am totally confused, but I think that put_user() simply should not fail
> this way. Say, why a syscall should return -EFAULT if memory allocation
> "silently" fails? Confused.

Seriously. I must have missed something, but I can't understand 519e52473eb
"mm: memcg: enable memcg OOM killer only for user faults".

The changelog says:

	System calls and kernel faults (uaccess, gup) can handle an out of
	memory situation gracefully and just return -ENOMEM.

How can a system call know it should return -ENOMEM if put_user() can only
return -EFAULT ?

Oleg.

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