sleep(3) sometimes too sleepy on FreeBSD 8.0?

[Kostik Belousov]

On Wed, Feb 24, 2010 at 06:53:59PM +1100, Peter Jeremy wrote:
> Updates following some off-line discussions and debugging with John on
> IRC.  I've cc'd gshapiro@ because the problem appears to be sendmail,
> rather than the FreeBSD kernel.
> 
> On 2010-Feb-23 12:35:22 +1100, John Marshall <john.marshall at riverwillow.com.au> wrote:
> >Environment: sendmail 8.14.4 on FreeBSD 8.0-RELEASE-p2
> 
> Note that this is stock ISC sendmail, not the sendmail in either the
> base system or the port.
> 
> >I posted about this in comp.mail.sendmail and was told...
> >
> >> sleep() should be one of these calls:
> >> 
> >>         if (njobs == 0 && WorkGrp[wgrp].wg_lowqintvl < MIN_SLEEP_TIME)
> >>                 sleep(MIN_SLEEP_TIME);
> >>         else if (WorkGrp[wgrp].wg_lowqintvl <= 0)
> >>                 sleep(QueueIntvl > 0 ? QueueIntvl : MIN_SLEEP_TIME);
> >>         else
> >>                 sleep(WorkGrp[wgrp].wg_lowqintvl);
> 
> Whilst it's true that the code calls sleep(), it's not calling
> sleep(3) in the FreeBSD libc.  Instead it's calling a sleep() defined
> in libsm/clock.c - which is a horrible maze of #ifdefs.
> 
> John has pre-processed that code and the result it at:
> http://www.riverwillow.net.au/~john/sm/clock.preprocessed
> 
> At a quick look, the code is broken: sm_seteventm() generates a
> one-off timer using setitimer(2), which will send SIGALRM when it
> expires.  sm_releasesignal() then unblocks SIGALRM.  In theory, the
> SIGALRM could be delivered anywhere after the (!SmSleepDone) test and
> before pause() is called - in which case, the signal is lost and
> pause() will sleep forever.
> 
> On 2010-Feb-24 08:13:06 +1100, John Marshall <john.marshall at riverwillow.com.au> wrote:
> >My ktrace file was created with 'ktrace -g 48501'.  I have the result of
> >'kdump -R -p 48504' available at:
> >
> > <http://www.riverwillow.net.au/~john/8_0/rwsrv04_201002240725.kdump.gz>
I get 'kdump: data too short' on RELENG_8/i386.

> 
> The syscall pattern near the end of this file is significantly different
> from that elsewhere in the file - with gettimeofday(), sigprocmask() and
> sigsuspend() looping fairly rapidly.  Interestingly, sigsuspend() is
> returning EINTR but no signal is reported.  I'm not sure what could
> cause this.
Is this 8.0-RELEASE ? Please note that kern_sigsuspend() code was
changed in HEAD/RELENG_8 after 8.0 release.

> 
> This syscall pattern looks like the while() loop in sendmail's sleep(),
> though it does appear that the loop is exited on that occasion but not
> on the following occasion (though the reason for this behaviour is
> unclear).
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