Messages in this thread | | | Subject | Re: [RFC 0/2] harden alloc_pages against bogus nid | From | Jeremy Linton <> | Date | Thu, 2 Aug 2018 22:15:10 -0500 |
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Hi,
On 08/01/2018 07:14 PM, Andrew Morton wrote: > On Wed, 1 Aug 2018 17:56:46 -0500 Jeremy Linton <jeremy.linton@arm.com> wrote: > >> Hi, >> >> On 08/01/2018 04:50 PM, Andrew Morton wrote: >>> On Wed, 1 Aug 2018 15:04:16 -0500 Jeremy Linton <jeremy.linton@arm.com> wrote: >>> >>>> The thread "avoid alloc memory on offline node" >>>> >>>> https://lkml.org/lkml/2018/6/7/251 >>>> >>>> Asked at one point why the kzalloc_node was crashing rather than >>>> returning memory from a valid node. The thread ended up fixing >>>> the immediate causes of the crash but left open the case of bad >>>> proximity values being in DSDT tables without corrisponding >>>> SRAT/SLIT entries as is happening on another machine. >>>> >>>> Its also easy to fix that, but we should also harden the allocator >>>> sufficiently that it doesn't crash when passed an invalid node id. >>>> There are a couple possible ways to do this, and i've attached two >>>> separate patches which individually fix that problem. >>>> >>>> The first detects the offline node before calling >>>> the new_slab code path when it becomes apparent that the allocation isn't >>>> going to succeed. The second actually hardens node_zonelist() and >>>> prepare_alloc_pages() in the face of NODE_DATA(nid) returning a NULL >>>> zonelist. This latter case happens if the node has never been initialized >>>> or is possibly out of range. There are other places (NODE_DATA & >>>> online_node) which should be checking if the node id's are > MAX_NUMNODES. >>>> >>> >>> What is it that leads to a caller requesting memory from an invalid >>> node? A race against offlining? If so then that's a lack of >>> appropriate locking, isn't it? >> >> There were a couple unrelated cases, both having to do with the PXN >> associated with a PCI port. The first case AFAIK, the domain wasn't >> really invalid if the entire SRAT was parsed and nodes created even when >> there weren't associated CPUs. The second case (a different machine) is >> simply a PXN value that is completely invalid (no associated >> SLIT/SRAT/etc entries) due to firmware making a mistake when a socket >> isn't populated. >> >> There have been a few other suggested or merged patches for the >> individual problems above, this set is just an attempt at avoiding a >> full crash if/when another similar problem happens. > > Please add the above info to the changelog.
Sure.
> >> >>> >>> I don't see a problem with emitting a warning and then selecting a >>> different node so we can keep running. But we do want that warning, so >>> we can understand the root cause and fix it? >> >> Yes, we do want to know when an invalid id is passed, i will add the >> VM_WARN in the first one. >> >> The second one I wasn't sure about as failing prepare_alloc_pages() >> generates a couple of error messages, but the system then continues >> operation. >> >> I guess my question though is which method (or both/something else?) is >> the preferred way to harden this up? > > The first patch looked neater. Can we get a WARN_ON in there as well? >
Yes,
Thanks,
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