Ubuntu
linux package

kernel log buffer to small...

Bug #424810 reported by Daniel J Blueman
8
This bug affects 1 person
Affects Status Importance Assigned to Milestone
linux (Ubuntu)
Fix Released
Medium
Tim Gardner
Karmic
Fix Released
Medium
Tim Gardner

Bug Description

Binary package hint: linux-image

When debugging a kernel problem, after eg a 'echo t >/proc/sysrq-trigger', the kernel log buffer simply overflows; 2^17 (128KB) is too small.

Fix is to change kernel configuration from:
CONFIG_LOG_BUF_SHIFT=17

to:
CONFIG_LOG_BUF_SHIFT=18

This would help in particular cases where we're reliant on this mechanism, for reporting/fixing kernel bugs.

Daniel J Blueman (danielblueman)
Changed in linux-meta (Ubuntu):
status: New → Confirmed
Revision history for this message
Daniel J Blueman (danielblueman) wrote :

When debugging the state of kernel tasks, eg by sending sysctrl-T, there is too much information with a typical login session for the default log buffer size, thus if the process is started earlier, the information is lost (either from dmesg, or /var/log/messages) and the first part of the output truncated:

$ cat /var/log/messages
Sep 19 11:42:32 exige kernel: [<ffffffff812732aa>] ? __up_read+0x9a/0xc0
Sep 19 11:42:32 exige kernel: [ 1803.421542] [<ffffffff811293f9>] do_vfs_ioctl+0x79/0x370
Sep 19 11:42:32 exige kernel: [ 1803.421542] [<ffffffff81077f79>] ? up_read+0x9/0x10
Sep 19 11:42:32 exige kernel: [ 1803.421542] [<ffffffff81525fe4>] ? do_page_fault+0x194/0x370
Sep 19 11:42:32 exige kernel: [ 1803.421542] [<ffffffff81129771>] sys_ioctl+0x81/0xa0
<snip>

I think it's important to be able to debug kernel problems fully, so this is a quick and safe fix.

Leann Ogasawara (leannogasawara)
affects: linux-meta (Ubuntu) → linux (Ubuntu)
Changed in linux (Ubuntu):
importance: Undecided → Medium
status: Confirmed → Triaged
Revision history for this message
Tim Gardner (timg-tpi) wrote :

How about raising it to 256K (2^18) for all flavours _except_ i386 generic?

Changed in linux (Ubuntu Karmic):
assignee: nobody → Tim Gardner (timg-tpi)
status: Triaged → In Progress
Revision history for this message
Daniel J Blueman (danielblueman) wrote :

This also benefits crashdump kernels, where the only kernel log messages may be available via the static kernel message buffer.

Keeping it at 128KB/2^17 for i386 seems entirely reasonable, in-line with keeping the memory requirements minimal, setting to 256KB/2^18 elsewhere.

Thanks!

Revision history for this message
Tim Gardner (timg-tpi) wrote :

http://kernel.ubuntu.com/git?p=ubuntu/ubuntu-karmic.git;a=commit;h=68625adedbf3e2a804254d636b3408f29877a708

Changed in linux (Ubuntu Karmic):
status: In Progress → Fix Committed
Revision history for this message
Launchpad Janitor (janitor) wrote :

This bug was fixed in the package linux - 2.6.31-11.37

---------------
linux (2.6.31-11.37) karmic; urgency=low

  [ Tim Gardner ]

  * [Config] Increase kernel log buffer to 256K for amd64 flavours
    - LP: #424810
  * [Config] Set HZ=100 for amd64 flavours
    - LP: #438234
  * [Upstream] e1000e: Emit notice instead of an error when
    pci_enable_pcie_error_reporting() fails
    - LP: #436370

  [ Upstream Kernel Changes ]

  * n_tty: honor opost flag for echoes
  * n_tty: move echoctl check and clean up logic
    - LP: #438310

  * Revert "[Upstream] drm/i915: Check that the relocation points to within
    the target" - Use upstream cherry-pick.
  * drm/i915: Check that the relocation points to within the target
    - LP: #429241

  * drm/i915: fix tiling on IGDNG
  * drm/i915: add B43 chipset support
  * agp/intel: Add B43 chipset support
    Intel request from kernel team mailing list.

  * HID: completely remove apple mightymouse from blacklist
    - LP: #428111

 -- Tim Gardner <email address hidden> Mon, 28 Sep 2009 11:47:29 -0600

Changed in linux (Ubuntu Karmic):
status: Fix Committed → Fix Released
To post a comment you must log in.
This report contains Public information  
Everyone can see this information.
Subscribing...

Other bug subscribers

Remote bug watches

Bug watches keep track of this bug in other bug trackers.