linux-kernel - 3.5 regressions related to printk changes

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Message-ID: <20120617150928.GJ8450@1wt.eu>
Date:	Sun, 17 Jun 2012 17:09:28 +0200
From:	Willy Tarreau <w@....eu>
To:	Kay Sievers <kay@...y.org>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-kernel@...r.kernel.org
Subject: 3.5 regressions related to printk changes

Hi Kay,

I was failing to get any 3.5-rc[123] kernel to boot on my dockstar (armv5).
I finally found some time today to bisect it and found that the responsible
commit was :

  From 7ff9554bb578ba02166071d2d487b7fc7d860d62 Mon Sep 17 00:00:00 2001
  From: Kay Sievers <kay@...y.org>
  Date: Thu, 3 May 2012 02:29:13 +0200
  Subject: [PATCH] printk: convert byte-buffer to variable-length record buffer

The symptom is that the kernel loads and hangs during early boot without
displaying anything. My config had CONFIG_EARLY_PRINTK enabled so I tried
without it again just in case it would be related, but it desperately did
not change anything, the kernel still fails to boot.

I have tried to revert printk changes on top of 3.5-rc3 and confirm that
now the kernel properly boots. Here's the list of what I reverted for
information :

    c313af145b9bc4fb8e8e0c83b8cfc10e1b894a50 printk() - isolate KERN_CONT users from ordinary complete lines
    3ce9a7c0ac28561567fadedf1a99272e4970f740 printk() - restore prefix/timestamp printing for multi-newline str
    1fce677971e29ceaa7c569741fa9c685a7b1052a printk: add stub for prepend_timestamp()
    f8450fca6ecdea38b5a882fdf6cd097e3ec8651c printk: correctly align __log_buf
    649e6ee33f73ba1c4f2492c6de9aff2254b540cb printk() - restore timestamp printing at console output
    5c5d5ca51abd728c8de3be43ffd6bb00f977bfcd printk() - do not merge continuation lines of different threads
    7f3a781d6fd81e397c3928c9af33f1fc63232db6 printk - fix compilation for CONFIG_PRINTK=n
    5fc3249068c1ed87c6fd485f42ced24132405629 kmsg: use do_div() to divide 64bit integer
    c4e00daaa96d3a0786f1f4fe6456281c60ef9a16 driver-core: extend dev_printk() to pass structured data
    e11fea92e13fb91c50bacca799a6131c81929986 kmsg: export printk records to the /dev/kmsg interface
    7ff9554bb578ba02166071d2d487b7fc7d860d62 printk: convert byte-buffer to variable-length record buffer

I understand that it will be hard to troubleshoot this with that little
information :-/

I'm not posting the config not to pollute the list, but have it available
if needed. I haven't noticed anything seemingly related on the list, but
if you want me to test a patch or to provide more information, feel free
to suggest !

I'm still checking if I can spot something.

Regards,
Willy

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