On 3/12/20 2:14 PM, Srikar Dronamraju wrote: > * Vlastimil Babka <vbabka@xxxxxxx> [2020-03-12 10:30:50]: > >> On 3/12/20 9:23 AM, Sachin Sant wrote: >> >> On 12-Mar-2020, at 10:57 AM, Srikar Dronamraju <srikar@xxxxxxxxxxxxxxxxxx> wrote: >> >> * Michal Hocko <mhocko@xxxxxxxxxx> [2020-03-11 12:57:35]: >> >>> On Wed 11-03-20 16:32:35, Srikar Dronamraju wrote: >> >>>> To ensure a cpuless, memoryless dummy node is not online, powerpc need >> >>>> to make sure all possible but not present cpu_to_node are set to a >> >>>> proper node. >> >>> >> >>> Just curious, is this somehow related to >> >>> http://lkml.kernel.org/r/20200227182650.GG3771@xxxxxxxxxxxxxx? >> >>> >> >> >> >> The issue I am trying to fix is a known issue in Powerpc since many years. >> >> So this surely not a problem after a75056fc1e7c (mm/memcontrol.c: allocate >> >> shrinker_map on appropriate NUMA node"). >> >> >> >> I tried v5.6-rc4 + a75056fc1e7c but didnt face any issues booting the >> >> kernel. Will work with Sachin/Abdul (reporters of the issue). > > I had used v1 and not v2. So my mistake. > >> > I applied this 3 patch series on top of March 11 next tree (commit d44a64766795 ) >> > The kernel still fails to boot with same call trace. >> > > While I am not an expert in the slub area, I looked at the patch > a75056fc1e7c and had some thoughts on why this could be causing this issue. > > On the system where the crash happens, the possible number of nodes is much > greater than the number of onlined nodes. The pdgat or the NODE_DATA is only > available for onlined nodes. > > With a75056fc1e7c memcg_alloc_shrinker_maps, we end up calling kzalloc_node > for all possible nodes and in ___slab_alloc we end up looking at the > node_present_pages which is NODE_DATA(nid)->node_present_pages. > i.e for a node whose pdgat struct is not allocated, we are trying to > dereference. >From what we saw, the pgdat does exist, the problem is that slab's per-node data doesn't exist for a node that doesn't have present pages, as it would be a waste of memory. Uh actually you are probably right, the NODE_DATA doesn't exist anymore? In Sachin's first report [1] we have [ 0.000000] numa: NODE_DATA [mem 0x8bfedc900-0x8bfee3fff] [ 0.000000] numa: NODE_DATA(0) on node 1 [ 0.000000] numa: NODE_DATA [mem 0x8bfed5200-0x8bfedc8ff] But in this thread, with your patches Sachin reports: [ 0.000000] numa: NODE_DATA [mem 0x8bfedc900-0x8bfee3fff] So I assume it's just node 1. In that case, node_present_pages is really dangerous. [1] https://lore.kernel.org/linux-next/3381CD91-AB3D-4773-BA04-E7A072A63968@xxxxxxxxxxxxxxxxxx/ > Also for a memoryless/cpuless node or possible but not present nodes, > node_to_mem_node(node) will still end up as node (atleast on powerpc). I think that's the place where this would be best to fix. > I tried with this hunk below and it works. > > But I am not sure if we need to check at other places were > node_present_pages is being called. I think this seems to defeat the purpose of node_to_mem_node()? Shouldn't it return only nodes that are online with present memory? CCing Joonsoo who seems to have introduced this in ad2c8144418c ("topology: add support for node_to_mem_node() to determine the fallback node") I think we do need well defined and documented rules around node_to_mem_node(), cpu_to_node(), existence of NODE_DATA, various node_states bitmaps etc so everyone handles it the same, safe way. > diff --git a/mm/slub.c b/mm/slub.c > index 626cbcbd977f..bddb93bed55e 100644 > --- a/mm/slub.c > +++ b/mm/slub.c > @@ -2571,9 +2571,13 @@ static void *___slab_alloc(struct kmem_cache *s, gfp_t gfpflags, int node, > if (unlikely(!node_match(page, node))) { > int searchnode = node; > > - if (node != NUMA_NO_NODE && !node_present_pages(node)) > - searchnode = node_to_mem_node(node); > - > + if (node != NUMA_NO_NODE) { > + if (!node_online(node) || !node_present_pages(node)) { > + searchnode = node_to_mem_node(node); > + if (!node_online(searchnode)) > + searchnode = first_online_node; > + } > + } > if (unlikely(!node_match(page, searchnode))) { > stat(s, ALLOC_NODE_MISMATCH); > deactivate_slab(s, page, c->freelist, c); > >> > >> >
