Re: [uml-devel] Occasional hang starting up.

[Werner Almesberger <wa@almesberger.net>]

Blaisorblade wrote:
> 2) write_sigio_thread should do a "down" on a semaphore/mutex and the first 
> update_thread should "up" it. As usually, this semaphore would be indeed 
> implemented as a pipe.

Be the way, in case a proper fix is too involved for 2.6.16.x,
here's a quick and dirty work-around that should have no ill
side-effects:

This hack works around a race condition that can make UML hang
on startup. If the race condition is encountered, this change
limits the time of the hang to one second. Besides that, it can
cause a small performance penalty by waking up an otherwise
idle "poll" every second.

This is intended purely as a readily applicable band aid and 
should not be considered a long-term fix.

- Werner

---------------------------------- cut here -----------------------------------

Signed-off-by: Werner Almesberger <werner@almesberger.net>

--- linux-2.6.16.orig/arch/um/kernel/sigio_user.c	2006-03-20 02:53:29.%N -0300
+++ linux-2.6.16/arch/um/kernel/sigio_user.c	2006-03-20 06:27:11.%N -0300
@@ -184,7 +184,7 @@
         signal(SIGWINCH, SIG_IGN);
 	fds = &current_poll;
 	while(1){
-		n = poll(fds->poll, fds->used, -1);
+		n = poll(fds->poll, fds->used, 1000);
 		if(n < 0){
 			if(errno == EINTR) continue;
 			printk("write_sigio_thread : poll returned %d, "

-- 
  _________________________________________________________________________
 / Werner Almesberger, Buenos Aires, Argentina         wa@almesberger.net /
/_http://www.almesberger.net/____________________________________________/


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