Re: [long]2.5.44-mm3 UP went into unexpected trashing

[Dipankar Sarma]

On Thu, Oct 24, 2002 at 12:01:31PM +0000, Ed Tomlinson wrote:
> Maneesh Soni wrote:
> >> Oh.  It was in -mm3 too.  But something went wrong with the
> >> dcache shrinking there.
> > 
> > Backing out larger-cpu-masks.patch fixes this in -mm3 so, -mm4 should not
> > give this problem. Basically callbacks are not getting processed due to
> > incorrect rcu_cpu_mask.
> 
> Would this affect UP systems?  Had the dentry leak on a UP box with 512m 
> memory.  About 400m ended up in unfreeable dentries...

It does affect UP systems.

A quick look at /proc/rcu in a leaky system indicated that somehow
despite having a batch of RCUs, they are not getting started.

 /* Fake initialization required by compiler */
@@ -106,10 +106,11 @@ static void rcu_start_batch(long newbatc
 		rcu_ctrlblk.maxbatch = newbatch;
 	}
 	if (rcu_batch_before(rcu_ctrlblk.maxbatch, rcu_ctrlblk.curbatch) ||
-	    (rcu_ctrlblk.rcu_cpu_mask != 0)) {
+	    (find_first_bit(rcu_ctrlblk.rcu_cpu_mask, NR_CPUS) != NR_CPUS)) {
 		return;
 	}
-	rcu_ctrlblk.rcu_cpu_mask = cpu_online_map;
+	memcpy(rcu_ctrlblk.rcu_cpu_mask, cpu_online_map,
+	       sizeof(rcu_ctrlblk.rcu_cpu_mask));
 }

Either find_first_bit() is not returning NR_CPUS when the bitmask has no
bit set or memcpy is not working on the UP version of cpu_online_map. Will
dig a little bit more.

Thanks
-- 
Dipankar Sarma  <[e-mail]> http://lse.sourceforge.net
Linux Technology Center, IBM Software Lab, Bangalore, India.