Sachin reports [1] a crash in SLUB __slab_alloc():

BUG: Kernel NULL pointer dereference on read at 0x000073b0 Faulting instruction address: 0xc0000000003d55f4 Oops: Kernel access of bad area, sig: 11 [#1] LE PAGE_SIZE=64K MMU=Hash SMP NR_CPUS=2048 NUMA pSeries Modules linked in: CPU: 19 PID: 1 Comm: systemd Not tainted 5.6.0-rc2-next-20200218-autotest #1 NIP: c0000000003d55f4 LR: c0000000003d5b94 CTR: 0000000000000000 REGS: c0000008b37836d0 TRAP: 0300 Not tainted (5.6.0-rc2-next-20200218-autotest) MSR: 8000000000009033 <SF,EE,ME,IR,DR,RI,LE> CR: 24004844 XER: 00000000 CFAR: c00000000000dec4 DAR: 00000000000073b0 DSISR: 40000000 IRQMASK: 1 GPR00: c0000000003d5b94 c0000008b3783960 c00000000155d400 c0000008b301f500 GPR04: 0000000000000dc0 0000000000000002 c0000000003443d8 c0000008bb398620 GPR08: 00000008ba2f0000 0000000000000001 0000000000000000 0000000000000000 GPR12: 0000000024004844 c00000001ec52a00 0000000000000000 0000000000000000 GPR16: c0000008a1b20048 c000000001595898 c000000001750c18 0000000000000002 GPR20: c000000001750c28 c000000001624470 0000000fffffffe0 5deadbeef0000122 GPR24: 0000000000000001 0000000000000dc0 0000000000000002 c0000000003443d8 GPR28: c0000008b301f500 c0000008bb398620 0000000000000000 c00c000002287180 NIP [c0000000003d55f4] ___slab_alloc+0x1f4/0x760 LR [c0000000003d5b94] __slab_alloc+0x34/0x60 Call Trace: [c0000008b3783960] [c0000000003d5734] ___slab_alloc+0x334/0x760 (unreliable) [c0000008b3783a40] [c0000000003d5b94] __slab_alloc+0x34/0x60 [c0000008b3783a70] [c0000000003d6fa0] __kmalloc_node+0x110/0x490 [c0000008b3783af0] [c0000000003443d8] kvmalloc_node+0x58/0x110 [c0000008b3783b30] [c0000000003fee38] mem_cgroup_css_online+0x108/0x270 [c0000008b3783b90] [c000000000235aa8] online_css+0x48/0xd0 [c0000008b3783bc0] [c00000000023eaec] cgroup_apply_control_enable+0x2ec/0x4d0 [c0000008b3783ca0] [c000000000242318] cgroup_mkdir+0x228/0x5f0 [c0000008b3783d10] [c00000000051e170] kernfs_iop_mkdir+0x90/0xf0 [c0000008b3783d50] [c00000000043dc00] vfs_mkdir+0x110/0x230 [c0000008b3783da0] [c000000000441c90] do_mkdirat+0xb0/0x1a0 [c0000008b3783e20] [c00000000000b278] system_call+0x5c/0x68

This is a PowerPC platform with following NUMA topology:

available: 2 nodes (0-1) node 0 cpus: node 0 size: 0 MB node 0 free: 0 MB node 1 cpus: 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 node 1 size: 35247 MB node 1 free: 30907 MB node distances: node 0 1 0: 10 40 1: 40 10

possible numa nodes: 0-31

This only happens with a mmotm patch "mm/memcontrol.c: allocate shrinker_map on appropriate NUMA node" [2] which effectively calls kmalloc_node for each possible node. SLUB however only allocates kmem_cache_node on online N_NORMAL_MEMORY nodes, and relies on node_to_mem_node to return such valid node for other nodes since commit a561ce00b09e ("slub: fall back to node_to_mem_node() node if allocating on memoryless node"). This is however not true in this configuration where the _node_numa_mem_ array is not initialized for nodes 0 and 2-31, thus it contains zeroes and get_partial() ends up accessing non-allocated kmem_cache_node.

A related issue was reported by Bharata (originally by Ramachandran) [3] where a similar PowerPC configuration, but with mainline kernel without patch [2] ends up allocating large amounts of pages by kmalloc-1k kmalloc-512. This seems to have the same underlying issue with node_to_mem_node() not behaving as expected, and might probably also lead to an infinite loop with CONFIG_SLUB_CPU_PARTIAL [4].

This patch should fix both issues by not relying on node_to_mem_node() anymore and instead simply falling back to NUMA_NO_NODE, when kmalloc_node(node) is attempted for a node that's not online, or has no usable memory. The "usable memory" condition is also changed from node_present_pages() to N_NORMAL_MEMORY node state, as that is exactly the condition that SLUB uses to allocate kmem_cache_node structures. The check in get_partial() is removed completely, as the checks in ___slab_alloc() are now sufficient to prevent get_partial() being reached with an invalid node.

[1] https://lore.kernel.org/linux-next/3381CD91-AB3D-4773-BA04-E7A072A63968@linu... [2] https://lore.kernel.org/linux-mm/fff0e636-4c36-ed10-281c-8cdb0687c839@virtuo... [3] https://lore.kernel.org/linux-mm/20200317092624.GB22538@in.ibm.com/ [4] https://lore.kernel.org/linux-mm/088b5996-faae-8a56-ef9c-5b567125ae54@suse.c...

Reported-and-tested-by: Sachin Sant sachinp@linux.vnet.ibm.com Reported-by: PUVICHAKRAVARTHY RAMACHANDRAN puvichakravarthy@in.ibm.com Tested-by: Bharata B Rao bharata@linux.ibm.com Debugged-by: Srikar Dronamraju srikar@linux.vnet.ibm.com Signed-off-by: Vlastimil Babka vbabka@suse.cz Fixes: a561ce00b09e ("slub: fall back to node_to_mem_node() node if allocating on memoryless node") Cc: stable@vger.kernel.org Cc: Mel Gorman mgorman@techsingularity.net Cc: Michael Ellerman mpe@ellerman.id.au Cc: Michal Hocko mhocko@kernel.org Cc: Christopher Lameter cl@linux.com Cc: linuxppc-dev@lists.ozlabs.org Cc: Joonsoo Kim iamjoonsoo.kim@lge.com Cc: Pekka Enberg penberg@kernel.org Cc: David Rientjes rientjes@google.com Cc: Kirill Tkhai ktkhai@virtuozzo.com Cc: Vlastimil Babka vbabka@suse.cz Cc: Nathan Lynch nathanl@linux.ibm.com --- Hi, after the RFC got positive test results from reporters, I'm resending as a proper patch. Thanks, Vlastimil

mm/slub.c | 26 +++++++++++++++++--------- 1 file changed, 17 insertions(+), 9 deletions(-)

diff --git a/mm/slub.c b/mm/slub.c index 17dc00e33115..7113b1f9cd77 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -1973,8 +1973,6 @@ static void *get_partial(struct kmem_cache *s, gfp_t flags, int node,

if (node == NUMA_NO_NODE) searchnode = numa_mem_id(); - else if (!node_present_pages(node)) - searchnode = node_to_mem_node(node);

object = get_partial_node(s, get_node(s, searchnode), c, flags); if (object || node != NUMA_NO_NODE) @@ -2563,17 +2561,27 @@ static void *___slab_alloc(struct kmem_cache *s, gfp_t gfpflags, int node, struct page *page;

page = c->page; - if (!page) + if (!page) { + /* + * if the node is not online or has no normal memory, just + * ignore the node constraint + */ + if (unlikely(node != NUMA_NO_NODE && + !node_state(node, N_NORMAL_MEMORY))) + node = NUMA_NO_NODE; goto new_slab; + } redo:

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 (unlikely(!node_match(page, searchnode))) { + /* + * same as above but node_match() being false already + * implies node != NUMA_NO_NODE + */ + if (!node_state(node, N_NORMAL_MEMORY)) { + node = NUMA_NO_NODE; + goto redo; + } else { stat(s, ALLOC_NODE_MISMATCH); deactivate_slab(s, page, c->freelist, c); goto new_slab;