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charset=us-ascii Content-Disposition: inline In-Reply-To: <20201027140926.276-1-ldufour@linux.ibm.com> X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: [Cc Vlastimil] On Tue 27-10-20 15:09:26, Laurent Dufour wrote: > While doing memory hot-unplug operation on a PowerPC VM running 1024 CPUs > with 11TB of ram, I hit the following panic: > > BUG: Kernel NULL pointer dereference on read at 0x00000007 > Faulting instruction address: 0xc000000000456048 > Oops: Kernel access of bad area, sig: 11 [#2] > LE PAGE_SIZE=64K MMU=Hash SMP NR_CPUS=2048 NUMA pSeries > Modules linked in: rpadlpar_io rpaphp > CPU: 160 PID: 1 Comm: systemd Tainted: G D 5.9.0 #1 > NIP: c000000000456048 LR: c000000000455fd4 CTR: c00000000047b350 > REGS: c00006028d1b77a0 TRAP: 0300 Tainted: G D (5.9.0) > MSR: 8000000000009033 CR: 24004228 XER: 00000000 > CFAR: c00000000000f1b0 DAR: 0000000000000007 DSISR: 40000000 IRQMASK: 0 > GPR00: c000000000455fd4 c00006028d1b7a30 c000000001bec800 0000000000000000 > GPR04: 0000000000000dc0 0000000000000000 00000000000374ef c00007c53df99320 > GPR08: 000007c53c980000 0000000000000000 000007c53c980000 0000000000000000 > GPR12: 0000000000004400 c00000001e8e4400 0000000000000000 0000000000000f6a > GPR16: 0000000000000000 c000000001c25930 c000000001d62528 00000000000000c1 > GPR20: c000000001d62538 c00006be469e9000 0000000fffffffe0 c0000000003c0ff8 > GPR24: 0000000000000018 0000000000000000 0000000000000dc0 0000000000000000 > GPR28: c00007c513755700 c000000001c236a4 c00007bc4001f800 0000000000000001 > NIP [c000000000456048] __kmalloc_node+0x108/0x790 > LR [c000000000455fd4] __kmalloc_node+0x94/0x790 > Call Trace: > [c00006028d1b7a30] [c00007c51af92000] 0xc00007c51af92000 (unreliable) > [c00006028d1b7aa0] [c0000000003c0ff8] kvmalloc_node+0x58/0x110 > [c00006028d1b7ae0] [c00000000047b45c] mem_cgroup_css_online+0x10c/0x270 > [c00006028d1b7b30] [c000000000241fd8] online_css+0x48/0xd0 > [c00006028d1b7b60] [c00000000024af14] cgroup_apply_control_enable+0x2c4/0x470 > [c00006028d1b7c40] [c00000000024e838] cgroup_mkdir+0x408/0x5f0 > [c00006028d1b7cb0] [c0000000005a4ef0] kernfs_iop_mkdir+0x90/0x100 > [c00006028d1b7cf0] [c0000000004b8168] vfs_mkdir+0x138/0x250 > [c00006028d1b7d40] [c0000000004baf04] do_mkdirat+0x154/0x1c0 > [c00006028d1b7dc0] [c000000000032b38] system_call_exception+0xf8/0x200 > [c00006028d1b7e20] [c00000000000c740] system_call_common+0xf0/0x27c > Instruction dump: > e93e0000 e90d0030 39290008 7cc9402a e94d0030 e93e0000 7ce95214 7f89502a > 2fbc0000 419e0018 41920230 e9270010 <89290007> 7f994800 419e0220 7ee6bb78 > > This pointing to the following code: > > mm/slub.c:2851 > if (unlikely(!object || !node_match(page, node))) { > c000000000456038: 00 00 bc 2f cmpdi cr7,r28,0 > c00000000045603c: 18 00 9e 41 beq cr7,c000000000456054 <__kmalloc_node+0x114> > node_match(): > mm/slub.c:2491 > if (node != NUMA_NO_NODE && page_to_nid(page) != node) > c000000000456040: 30 02 92 41 beq cr4,c000000000456270 <__kmalloc_node+0x330> > page_to_nid(): > include/linux/mm.h:1294 > c000000000456044: 10 00 27 e9 ld r9,16(r7) > c000000000456048: 07 00 29 89 lbz r9,7(r9) <<<< r9 = NULL > node_match(): > mm/slub.c:2491 > c00000000045604c: 00 48 99 7f cmpw cr7,r25,r9 > c000000000456050: 20 02 9e 41 beq cr7,c000000000456270 <__kmalloc_node+0x330> > > The panic occurred in slab_alloc_node() when checking for the page's node: > object = c->freelist; > page = c->page; > if (unlikely(!object || !node_match(page, node))) { > object = __slab_alloc(s, gfpflags, node, addr, c); > stat(s, ALLOC_SLOWPATH); > > The issue is that object is not NULL while page is NULL which is odd but > may happen if the cache flush happened after loading object but before > loading page. Thus checking for the page pointer is required too. Could you be more specific? I am especially confused how the memory hotplug is involved here. What kind of flush are we talking about? > In commit 6159d0f5c03e ("mm/slub.c: page is always non-NULL in > node_match()") check on the page pointer has been removed assuming that > page is always valid when it is called. It happens that this is not true in > that particular case, so check for page before calling node_match() here. > > Fixes: 6159d0f5c03e ("mm/slub.c: page is always non-NULL in node_match()") > Signed-off-by: Laurent Dufour > Cc: Christoph Lameter > Cc: Pekka Enberg > Cc: David Rientjes > Cc: Joonsoo Kim > Cc: Andrew Morton > Cc: stable@vger.kernel.org > --- > mm/slub.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/mm/slub.c b/mm/slub.c > index 8f66de8a5ab3..7dc5c6aaf4b7 100644 > --- a/mm/slub.c > +++ b/mm/slub.c > @@ -2852,7 +2852,7 @@ static __always_inline void *slab_alloc_node(struct kmem_cache *s, > > object = c->freelist; > page = c->page; > - if (unlikely(!object || !node_match(page, node))) { > + if (unlikely(!object || !page || !node_match(page, node))) { > object = __slab_alloc(s, gfpflags, node, addr, c); > } else { > void *next_object = get_freepointer_safe(s, object); > -- > 2.29.1 > -- Michal Hocko SUSE Labs