linux-kernel - Re: [PATCH] efibc: avoid stack overflow warning

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Message-ID: <20160430224641.GQ2839@codeblueprint.co.uk>
Date:	Sat, 30 Apr 2016 23:46:41 +0100
From:	Matt Fleming <matt@...eblueprint.co.uk>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	"Compostella, Jeremy" <jeremy.compostella@...el.com>,
	Ingo Molnar <mingo@...nel.org>, linux-efi@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] efibc: avoid stack overflow warning

On Sun, 01 May, at 12:34:29AM, Arnd Bergmann wrote:
> 
> The sys_restart() system call takes a mutex before calling kernel_restart()
> or kernel_poweroff().
> 
> I've had a closer look now and found that there are a few other
> callers of kernel_restart, so I guess if you restart using sysctl
> at the exact same time as calling /sbin/reboot, things may break.
 
Right. Or if the dm-verify-target driver saw an error.

> It's not something we'd have to worry about in practice, but it does
> make my patch incorrect. Should we come up with a different way to
> do it?

Jeremy proposed a patch to dynamically allocate the memory, which I
think is the correct way to go given that our (reasonable) assumptions
about reboot notifier concurrency are not guaranteed,

  https://lkml.kernel.org/r/87h9eked24.fsf@jcompost-MOBL1.tl.intel.com