sleep(3) sometimes too sleepy on FreeBSD 8.0?

[John Marshall]

On Wed, 24 Feb 2010, 14:20 +0200, Kostik Belousov wrote:
> On Wed, Feb 24, 2010 at 03:44:41AM -0800, Jeremy Chadwick wrote:
> > On Wed, Feb 24, 2010 at 01:21:39PM +0200, Kostik Belousov wrote:
> > > 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>

> Regarding sigsuspend() returning EINTR without delivering any signal,
> could it be that the sendmail process was debugged ?

No.  I didn't touch the process with anything this time.  There was no
debugger in use on the system.  That was how I found the process first
thing this morning so I sent off the kdump output.

The process stayed in the same state until I rebooted the system this
afternoon to install a kernel with debug symbols and options.  I have
done the same on the other two servers, so I can dig deeper for you next
time.  I am running ktrace on the sendmail process group on all three
servers waiting to catch the next one.  By the way, all three are i386
with SMP.

-- 
John Marshall
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