threads/89262: [kernel] [patch] multi-threaded process hangs in kernel in fork()

[John Baldwin]

The following reply was made to PR threads/89262; it has been noted by GNATS.

From: John Baldwin <jhb at freebsd.org>
To: David Xu <davidxu at freebsd.org>
Cc: bug-followup at freebsd.org, garry at networkphysics.com
Subject: Re: threads/89262: [kernel] [patch] multi-threaded process hangs in kernel in fork()
Date: Mon, 13 Feb 2006 13:02:42 -0500

 On Monday 13 February 2006 04:11, David Xu wrote:
 > ast will call userret which in turn will call thread_suspend_check.
 > so the bug may not be here, but in other code.
 >
 > I have found a race between sleep queue and thread suspension code,
 > the following patch fixed the bug, it also simplified interaction
 > between sleep queue and signal code. now, sleepq_abort() is also
 > fixed, it can save an errno, unlike current code, it wrongly works
 > as wakeup().
 >
 > http://people.freebsd.org/~davidxu/patch/slpq_susp4.patch
 >
 > David Xu
 
 Only thing I would prefer is that you keep sleepq_catch_signals() but make it 
 an internal function that sleepq_waitsig() and sleepq_timed_waitsig() call 
 before sleepq_switch() so that sleepq_switch() doesn't get so long.  Also, it 
 would be good.  Also, in sleepq_switch() you are using sleepq_release() and 
 sleepq_lock() even though you already have a sleepqueue_chain pointer, and 
 you do mtx operations on sc->sc_lock explicitly in some other places.  It 
 would be best to consistently just do mutex ops on sc->sc_lock instead of 
 redoing the hash-lookup several times.
 
 -- 
 John Baldwin <jhb at FreeBSD.org>  <><  http://www.FreeBSD.org/~jhb/
 "Power Users Use the Power to Serve"  =  http://www.FreeBSD.org