* Vlastimil Babka <vbabka@xxxxxxx> [2020-03-20 12:55:32]:
> 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@xxxxxxxxxxxxxxxxxx/
> [2] https://lore.kernel.org/linux-mm/fff0e636-4c36-ed10-281c-8cdb0687c839@xxxxxxxxxxxxx/
> [3] https://lore.kernel.org/linux-mm/20200317092624.GB22538@xxxxxxxxxx/
> [4] https://lore.kernel.org/linux-mm/088b5996-faae-8a56-ef9c-5b567125ae54@xxxxxxx/
>
> Reported-and-tested-by: Sachin Sant <sachinp@xxxxxxxxxxxxxxxxxx>
> Reported-by: PUVICHAKRAVARTHY RAMACHANDRAN <puvichakravarthy@xxxxxxxxxx>
> Tested-by: Bharata B Rao <bharata@xxxxxxxxxxxxx>
> Debugged-by: Srikar Dronamraju <srikar@xxxxxxxxxxxxxxxxxx>
> Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx>
> Fixes: a561ce00b09e ("slub: fall back to node_to_mem_node() node if allocating on memoryless node")
Reviewed-by: Srikar Dronamraju <srikar@xxxxxxxxxxxxxxxxxx>
--
Thanks and Regards
Srikar Dronamraju
