linux-kernel - Re: [2.6.21.1] resume doesn't run suspended kernel?

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Message-ID: <4659442E.2060307@dgreaves.com>
Date:	Sun, 27 May 2007 09:41:18 +0100
From:	David Greaves <david@...eaves.com>
To:	Bill Davidsen <davidsen@....com>
Cc:	Linux Kernel M/L <linux-kernel@...r.kernel.org>
Subject: Re: [2.6.21.1] resume doesn't run suspended kernel?

Bill Davidsen wrote:
> Anyway, I pulled the plug on the UPS, and the system shut down. But when
> it powered up, it booted the default kernel rather than the test kernel,
> decided that it couldn't resume, and then did a cold boot.

Booting the machine isn't the kernel's job, it's the bootloader's job.

> I can bypass this by making the debug kernel the default, but WHY? Is
> the kernel not saved such that any kernel can be rolled back into memory
> and run? Actually, the answer is HELL NO, so I really ask if this is the
> intended mode of operation, that only the default boot kernel will restore.

Yes.

It is very dangerous to attempt a resume with a different kernel than the one
that has gone to sleep.
Different kernels may be compiled with different options that affect where or
how in-memory structures are saved.

So you suspend with a kernel which holds your filesystem data/cache/inodes at
0x1234000 and restore with a kernel that expects to see your filesystem data at
0x1235000.

Ouch.

Personally I think the kernel suspend should write a signature - similar to a
hash of the bzImage - into the suspend image so it won't even attempt a resume
if there's a mismatch. (Yes, I made this mistake once whilst playing with suspend).

David

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