Re: 2.4.7p6 hang

[Trond Myklebust <trond.myklebust@fys.uio.no>]

>>>>> " " == Andrea Arcangeli <andrea@suse.de> writes:

     > ksoftirqd is quite scheduler intensive, and while its startup
     > is correct (no need of any change there), it tends to trigger
     > scheduler bugs (one of those bugs was just fixed in pre5). The
     > reason I never seen the deadlock I also fixed this other
     > scheduler bug in my tree:

     > --- 2.4.4aa3/kernel/sched.c.~1~ Sun Apr 29 17:37:05 2001
     > +++ 2.4.4aa3/kernel/sched.c Tue May 1 16:39:42 2001
     > @@ -674,8 +674,10 @@
     >  #endif
     >  	spin_unlock_irq(&runqueue_lock);
 
     > - if (prev == next)
     > + if (prev == next) {
     > + current->policy &= ~SCHED_YIELD;
     >  		goto same_process;
     > + }
 
     >  #ifdef CONFIG_SMP
     >   	/*

I no longer see the hang with this patch, but I'm not sure I
understand why it works.
Does the above mean that the hang is occuring because spawn_ksoftirqd
is yielding back to itself? If so, the semaphore trick seems more
robust, as it causes a proper sleep until it's safe to wake up.

Cheers,
  Trond