Linux image contains buggy alternatives code

See this posting:

http://lkml.org/lkml/2006/10/16/299

Thanks for taking the time to report this bug. Unfortunately we can't fix it, because your description didn't include enough information.

Please include the following additional information, if you have not already done so (please pay attention to lspci's additional options), as required by the Ubuntu Kernel Team:

0. Pliss update you BIOS.
1. Please include the output of the command "uname -a" in your next response. It should be one, long line of text which includes the exact kernel version you're running, as well as the CPU architecture.
2. Please run the command "dmesg > dmesg.log" and attach the resulting file "dmesg.log" to this bug report.
3. Please run the command "lspci -vvnn > lspci-vvnn.log" and attach the resulting file "lspci-vvnn.log" to this bug report.
4. Please run the command "sudo dmidecode > dmidecode.log" and attach the resulting file "dmidecode.log" to this bug report.

For your reference, the full description of procedures for kernel-related bug reports is available here: <http://wiki.ubuntu.com/DebuggingKernelProblems> Thanks!

Change status of Unconfirmed to Needs Info.

I will post the information that you requested later. I am surprised, though that the information I provided was not sufficient. The link which I provided (http://lkml.org/lkml/2006/10/16/299) contains both the LKML discussion of the bug and the patch required to fix it. I have checked the Edgy kernel sources, and the patch clearly applies to them (there are no Ubuntu-specific changes to the affected function against vanilla 2.6.18, from whence the function was backported).

Included below is the information you requested. uname -a says:

Linux test-desktop 2.6.17-10-generic #2 SMP Tue Dec 5 22:28:26 UTC 2006 i686 GNU/Linux

Note that:

1) The bug can be worked around by specifying the "noreplacement" kernel option
2) The bug has also been backported to the Dapper SMP kernel, but without the workaround
3) As I said, this is the patch to arch/i386/kernel/alternative.c which fixes the problem:

 void __init alternative_instructions(void)
 {
+ unsigned long flags;
  if (no_replacement) {
   printk(KERN_INFO "(SMP-)alternatives turned off\n");
   free_init_pages("SMP alternatives",
@@ -396,6 +397,8 @@ void __init alternative_instructions(voi
     (unsigned long)__smp_alt_end);
   return;
  }
+
+ local_irq_save(flags);
  apply_alternatives(__alt_instructions, __alt_instructions_end);

  /* switch to patch-once-at-boottime-only mode and free the
@@ -433,4 +436,5 @@ void __init alternative_instructions(voi
  alternatives_smp_switch(0);
 }
#endif
-}
+ local_irq_restore(flags);
+}

Sorry, above patch was just cut and pasted and does not quite match the current Edgy kernel. The attached diff was against the Edgy kernel.

The information you posted was sufficient, Cristian is just using a cut & paste solution and not reading your report at all. Please ignore him, he doesn't know what he's doing.

Will fix this in the next security upload.

Will this also get fixed on the installer CDs? It affects quite a few people installing to virtual machines.

New CD images will be available next week with the release of 7.04, and will include this fix

Will that include a new Dapper server image? I can see that the Edgy CD images will be less relevant after Feisty is released.