Udev occasionally does not write log priority change messages

Bug #1208929 reported by Richard Michael
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udev (Ubuntu)
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Bug Description

"udevadm control --log-priority=XXX" normally causes udevd to write a message to syslog indicating it has received SET_LOG_PRIORITY message and the resulting (and now current) log priority.

I expect udevd to consistently write notification messages, but occasionally it does not. Aside, I am uncertain if it has actually changed priority in the cases when it fails to write the notification messages. Often, when udevd drops the log change messages, it seems to be also dropping other event messages. So I suspect the failure to write messages might not be unique to the SET_LOG_PRIORITY message type.

strace shows udevd has received the signal, but not written the message: after receiving some messages, it does not call the time() or send() syscalls.

I suspected udevd might be *not* writing messages when the "new" priority is the same as the current priority, e.g. "udevadm control --log-priority=debug" twice in a row. But this is not the case: under normal operation udevd does indeed write "change" notifications for both udevadm invocations.

Note, I have disabled rsyslogd's buffered logging ($RepeatedMsgReduction off). Although, given the missing syscalls, this seems to be a behaviour of udevd, independent of the syslog implementation.

I have attached output of several invocations of udevdadm, the log messages written by udevd and corresponding strace output; with timestamps and comments.

(ubuntu) ~ lsb_release -rd
Description: Ubuntu 12.04.2 LTS
Release: 12.04

(ubuntu) ~ apt-cache policy udev
udev:
  Installed: 175-0ubuntu9.4
  Candidate: 175-0ubuntu9.4
  Version table:
 *** 175-0ubuntu9.4 0
        500 http://us.archive.ubuntu.com/ubuntu/ precise-updates/main i386 Packages
        100 /var/lib/dpkg/status
     175-0ubuntu9 0
        500 http://us.archive.ubuntu.com/ubuntu/ precise/main i386 Packages

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Richard Michael (rmichael) wrote :
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