linux-kernel - Re: [v4 PATCH 1/1] init: fix race between rootfs mount and firmware loading

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Date:	Fri, 19 Sep 2014 21:45:47 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Roman Pen <r.peniaev@...il.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:	Ming Lei <ming.lei@...onical.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [v4 PATCH 1/1] init: fix race between rootfs mount and
	firmware loading

On 09/19, Roman Pen wrote:
>
> +void wait_for_rootfs(void)
> +{
> +	/* Here we try to protect from a few things:
> +	 * 1. Avoid waiting for ourselves, when init thread has not
> +	 *    mounted rootfs yet.
> +	 * 2. Avoid warning if call chain was initiated from userspace
> +	 *    /sbin/init. For example when /sbin/init loads the driver,
> +	 *    which, in turn, wants to access rootfs (e.g. firmware loading),
> +	 *    thus it has to be sure, that rootfs has been successfully
> +	 *    mounted.
> +	 */
> +	if (rootfs_mounted || WARN_ON(is_global_init(current)))
> +		return;
> +	else
> +		wait_event(rootfs_waitq, rootfs_mounted);
> +}

Well, in this case __wait_event() makes more sense, we already checked
rootfs_mounted, but this is minor.

Reviewed-by: Oleg Nesterov <oleg@...hat.com>


But I hope that Greg can take a look too. I do not understand the problem
space enough, so I am not sure this is the "right" fix. Say, perhaps we
should change the drivers which abuse request_firmware(), or do something
else.

Oleg.

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