Re: [BUG] at mm/slab.c:3320

[Christoph Lameter <clameter@sgi.com>]

On Tue, 8 Jan 2008, KAMEZAWA Hiroyuki wrote:

> In usual alloc_pages() allocator, this is done by zonelist fallback.

Hmmm... __cache_alloc_node does:

    if (unlikely(!cachep->nodelists[nodeid])) {
                /* Node not bootstrapped yet */
                ptr = fallback_alloc(cachep, flags);
                goto out;
        }

So kmalloc_node does the correct fallback.

Kmalloc does not fall back but relies on numa_node_id() referring to a 
node that has ZONE_NORMAL memory. Sigh.

cache_alloc_refill:

        node = numa_node_id();

        check_irq_off();
        ac = cpu_cache_get(cachep);
retry:
        batchcount = ac->batchcount;
        if (!ac->touched && batchcount > BATCHREFILL_LIMIT) {
                /*
                 * If there was little recent activity on this cache, then
                 * perform only a partial refill.  Otherwise we could generate
                 * refill bouncing.
                 */
                batchcount = BATCHREFILL_LIMIT;
        }
        l3 = cachep->nodelists[node];

	BUG_ON(ac->avail > 0 || !l3);
	^^^^ triggers


> complicated ?

Hmm.. We could check for l3 == NULL and fail in that case? The 
___cache_alloc would fail and __do_cache_alloc would call 
___cache_alloc_node whicvh would provide the correct fallback.

Doesd this fix it?


---
 mm/slab.c |    5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

Index: linux-2.6/mm/slab.c
===================================================================
--- linux-2.6.orig/mm/slab.c	2008-01-07 21:37:34.000000000 -0800
+++ linux-2.6/mm/slab.c	2008-01-07 21:38:09.000000000 -0800
@@ -2977,7 +2977,10 @@ retry:
 	}
 	l3 = cachep->nodelists[node];
 
-	BUG_ON(ac->avail > 0 || !l3);
+	if (!l3)
+		return NULL;
+
+	BUG_ON(ac->avail > 0);
 	spin_lock(&l3->list_lock);
 
 	/* See if we can refill from the shared array */

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