[PATCH] do not free non slab allocated per_cpu_pageset

[David Rientjes <rientjes@cs.washington.edu>]

On Thu, 21 Sep 2006, David Rientjes wrote:

> The _only_ time zone_pcp is slab allocated is through process_zones().  So 
> if we have an error on kmalloc_node for that zone_pcp, all previous 
> allocations are freed and process_zones() fails for that cpu.
> 
> We are guaranteed that the process_zones() for cpu 0 succeeds, otherwise 
> the pageset notifier isn't registered.  On CPU_UP_PREPARE for cpu 4 in 
> this case, process_zones() fails because we couldn't kmalloc the 
> per_cpu_pageset and we return NOTIFY_BAD.  This prints the failed message 
> in the report and then CPU_UP_CANCELED is sent back to the notifier which 
> attempts to kfree the zone that was never kmalloc'd.
> 
> The fix will work except for the case that zone_pcp is never set to NULL 
> as it should be.
> 

As reported by Keith, the following 2.6.18 patch stops the panic 
associated with attempting to free a non slab-allocated per_cpu_pageset.

Signed-off-by: David Rientjes <rientjes@cs.washington.edu>
---
 mm/page_alloc.c |    4 +++-
 1 files changed, 3 insertions(+), 1 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 54a4f53..e16173f 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1845,8 +1845,10 @@ static inline void free_zone_pagesets(in
 	for_each_zone(zone) {
 		struct per_cpu_pageset *pset = zone_pcp(zone, cpu);
 
+		/* Free per_cpu_pageset if it is slab allocated */
+		if (pset != &boot_pageset[cpu])
+			kfree(pset);
 		zone_pcp(zone, cpu) = NULL;
-		kfree(pset);
 	}
 }
 
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