(2014/12/01 7:16), Paul Mackerras wrote:
The bounds check for nodeid in ____cache_alloc_node gives false positives on machines where the node IDs are not contiguous, leading to a panic at boot time. For example, on a POWER8 machine the node IDs are typically 0, 1, 16 and 17. This means that num_online_nodes() returns 4, so when ____cache_alloc_node is called with nodeid = 16 the VM_BUG_ON triggers.
Do you have the call trace? If you have it, please add it in the description.
To fix this, we instead compare the nodeid with MAX_NUMNODES, and additionally make sure it isn't negative (since nodeid is an int). The check is there mainly to protect the array dereference in the get_node() call in the next line, and the array being dereferenced is of size MAX_NUMNODES. If the nodeid is in range but invalid, the BUG_ON in the next line will catch that. Signed-off-by: Paul Mackerras <paulus@xxxxxxxxx>
Do you need to backport it into -stable kernels?
--- diff --git a/mm/slab.c b/mm/slab.c index eb2b2ea..f34e053 100644 --- a/mm/slab.c +++ b/mm/slab.c @@ -3076,7 +3076,7 @@ static void *____cache_alloc_node(struct kmem_cache *cachep, gfp_t flags, void *obj; int x;
- VM_BUG_ON(nodeid > num_online_nodes()); + VM_BUG_ON(nodeid < 0 || nodeid >= MAX_NUMNODES);
How about use: VM_BUG_ON(!node_online(nodeid)); When allocating the memory, the node of the memory being allocated must be online. But your code cannot check the condition. Thanks, Yasuaki Ishimatsu
n = get_node(cachep, nodeid); BUG_ON(!n); -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
-- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>