linux-kernel - Re: [PATCH] shm: fix a race between shm_exit() and shm

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Message-ID: <CAPXgP12Ocdcmh7USsPv+WzYFTSh3EFi++q7YWop-XEUjrXfQAw@mail.gmail.com>
Date:	Wed, 3 Aug 2011 15:33:27 +0200
From:	Kay Sievers <kay.sievers@...y.org>
To:	Thadeu Lima de Souza Cascardo <cascardo@...aslivre.org>
Cc:	linux-kernel@...r.kernel.org, marc.zyngier@....com,
	manuel.lauss@...glemail.com, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, segoon@...nwall.com, richard@....at,
	gregkh@...e.de
Subject: Re: [PATCH] shm: fix a race between shm_exit() and shm_init()

On Wed, Aug 3, 2011 at 15:13, Thadeu Lima de Souza Cascardo
<cascardo@...aslivre.org> wrote:
> As Marc Zyngier has pointed out, the culprit is driver_init, which
> calls devices_init. I'd say other calls from driver_init also call into
> kset and kobject, which will dispatch uevent helper.
>
> I tried to reproduce the problem using UML and only was successful after
> setting CONFIG_UEVENT_HELPER_PATH. I guess we could obsolete this
> feature and plan its removal soon. Is anybody still using this?

Forking binaries from the kernel for frequent events is something
fundamentally wrong to do. It is not even rate-limited or has any
upper bounds. It is known to create out-of-memory situations on
machines with many devices and tiny RAM. Configs that virtualizations
with many guests use pretty often. They can not even bootup with
/sbin/hotplug enabled then.

It would be nice to remove that broken thing, no common system or
distro uses it since quite some years now. But I wouldn't be surprised
if some people still use it for whatever hack they need locally.

Kay
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