On Mon, Dec 01, 2014 at 04:02:14PM +1100, Michael Ellerman wrote: > On Mon, 2014-12-01 at 15:28 +1100, 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, like this: > ... > > > > 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 (for > > example if the node is off-line), the BUG_ON in the next line will > > catch that. > > When did this break? How come we only just noticed? Commit 14e50c6a9bc2, which went into 3.10-rc1. You'll only notice if you have CONFIG_SLAB=y and CONFIG_DEBUG_VM=y and you're running on a machine with discontiguous node IDs. > Also needs: > > Cc: stable@xxxxxxxxxxxxxxx It does. I remembered that a minute after I sent the patch. Paul. -- 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>