Messages in this thread | | | Subject | Re: [PATCH v2] slab: Fix nodeid bounds check for non-contiguous node IDs | From | Michael Ellerman <> | Date | Mon, 01 Dec 2014 19:52:21 +1100 |
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On Mon, 2014-12-01 at 16:24 +1100, Paul Mackerras wrote: > 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.
OK. So a Fixes tag is nice:
Fixes: 14e50c6a9bc2 ("mm: slab: Verify the nodeid passed to ____cache_alloc_node")
> 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.
Right. And we have SLUB=y for all the defconfigs that are likely to hit that.
> > Also needs: > > > > Cc: stable@vger.kernel.org > > It does. I remembered that a minute after I sent the patch.
OK. Hopefully one of the slab maintainers will be happy to add it for us when they merge this?
cheers
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