linux-kernel - [2.6.18-rc7] printk output delay in syslog wrt dmesg still unfixed

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Date:	Sat, 16 Sep 2006 14:45:00 +0200
From:	Tilman Schmidt <tilman@...p.cc>
To:	linux-kernel@...r.kernel.org
CC:	john stultz <johnstul@...ibm.com>
Subject: [2.6.18-rc7] printk output delay in syslog wrt dmesg still unfixed

The following problem, which I reported for kernel 2.6.18-rc1 on my
development machine
  Dell OptiPlex GX110
  uname -a = Linux gx110 2.6.18-rc7-noinitrd #1 PREEMPT Thu Sep 14
15:13:38 CEST 2006 i686 i686 i386 GNU/Linux
  933 MHz Pentium III processor, i810 chipset, 512 MB RAM
  distribution SuSE 10.0, syslog-ng 1.6.8, klogd 1.4.1, Xorg X11 6.8.2
still exists with 2.6.18-rc7:

While X is running, output from printk() appears in syslog (eg.
/var/log/messages) only after a key is pressed on the system keyboard,
even though it is visible with dmesg immediately.

Additional observations:
- The problem is *not* present with 2.6.17.* or earlier kernels.
- The problem *is* present with 2.6.18-rc*-mm* kernels.
- The problem disappears if the X server is terminated (telinit 3) and
  reappears if the X server is started again (telinit 5).
- Syslog messages from userspace programs are not affected by the delay.
- No messages are lost, all appear eventually, though possibly hours
  or days later, depending on how long nobody touches the keyboard.
- It doesn't matter which key is pressed; even pressing a shift key all
  by its own is sufficient to make the missing messages appear.
- I couldn't find any other action that would release the messages;
  neither mouse movements or clicks, nor waiting up to 24 hours, not
  even logging in via ssh from another machine and compiling a Linux
  kernel. ;-)
- The effect can be clearly observed by the difference between the
  kernel's own timestamps and those by syslogd; an extreme example:

Sep 16 14:11:16 gx110 kernel: [18729.057746] gigaset: unblocking all
channels
Sep 16 14:11:16 gx110 kernel: [18729.057765] gigaset: searching
scheduled commands
Sep 16 14:11:16 gx110 kernel: [86033.298803] gigaset: received response
(8 bytes): ^M^JZLOG^M^J
Sep 16 14:11:16 gx110 kernel: [86033.298898] bas_gigaset: cmd_loop: End
of Command (0 Bytes)

Please let me know if I can help in any way with locating the cause of
this annoying phenomenon.

Thanks
Tilman

-- 
Tilman Schmidt                          E-Mail: tilman@...p.cc
Bonn, Germany
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