i386 hangs during halt "vnodes remaining... 0 time out"

[Konstantin Belousov]

On Sun, Apr 22, 2018 at 03:15:00PM +0200, Tijl Coosemans wrote:
> On Sun, 22 Apr 2018 15:05:21 +0300 Konstantin Belousov <kostikbel at gmail.com> wrote:
> > On Sat, Apr 21, 2018 at 11:49:34PM +0200, Tijl Coosemans wrote:
> >> On Sat, 21 Apr 2018 21:09:09 +0000 Rick Macklem <rmacklem at uoguelph.ca> wrote:  
> >>> With a recent head/current kernel (doesn't happen when running a Dec.
> >>> 2017 one), when I do a halt, it gets as far as:
> >>> 
> >>> vnodes remaining... 0 time out
> >>> 
> >>> and that's it (the time out appears several seconds after the first "0").
> >>> With a Dec. 2017 kernel there would be several "0"s printed.
> >>> It appears that it is stuck in the first iteration of the sched_sync()
> >>> loop after it is no longer in SYNCER_RUNNING state.
> >>> 
> >>> Any ideas? rick  
> >> 
> >> See https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=227404
> >> I have a patch (attached) but haven't been able to test it yet.  
> >> 
> >> Index: sys/kern/vfs_bio.c
> >> ===================================================================
> >> --- sys/kern/vfs_bio.c	(revision 332165)
> >> +++ sys/kern/vfs_bio.c	(working copy)
> >> @@ -791,9 +791,12 @@ bufspace_daemon(void *arg)
> >>  {
> >>  	struct bufdomain *bd;
> >>  
> >> +	EVENTHANDLER_REGISTER(shutdown_pre_sync, kthread_shutdown, curthread,
> >> +	    SHUTDOWN_PRI_LAST);
> >> +
> >>  	bd = arg;
> >>  	for (;;) {
> >> -		kproc_suspend_check(curproc);
> >> +		kthread_suspend_check();
> >>  
> >>  		/*
> >>  		 * Free buffers from the clean queue until we meet our
> >> @@ -3357,7 +3360,7 @@ buf_daemon()
> >>  	/*
> >>  	 * This process needs to be suspended prior to shutdown sync.
> >>  	 */
> >> -	EVENTHANDLER_REGISTER(shutdown_pre_sync, kproc_shutdown, bufdaemonproc,
> >> +	EVENTHANDLER_REGISTER(shutdown_pre_sync, kthread_shutdown, curthread,
> >>  	    SHUTDOWN_PRI_LAST);
> >>  
> >>  	/*
> >> @@ -3381,7 +3384,7 @@ buf_daemon()
> >>  		bd_request = 0;
> >>  		mtx_unlock(&bdlock);
> >>  
> >> -		kproc_suspend_check(bufdaemonproc);
> >> +		kthread_suspend_check();
> >>  
> >>  		/*
> >>  		 * Save speedupreq for this pass and reset to capture new  
> > This looks fine.
> 
> Thanks for the review.  There's just one concern I have.  With this patch
> the bufspace_daemon threads appear to shutdown after the buf_daemon and
> after the syncer because the event handlers are registered later.  Are
> there any dependencies between these processes that require the bufspace
> threads to be stopped earlier?

I think for correctness bufdaemon must stop after the syncer, since syncer
operation can cause a situation where bufdaemon help is needed to proceed.
Other than this, the stop order is irrelevant, because after syncer finished,
there should be no any further filesystem activity.