On Fri 09-11-18 16:34:29, Anshuman Khandual wrote: > > > On 11/09/2018 01:29 PM, Michal Hocko wrote: > > On Fri 09-11-18 09:12:09, Anshuman Khandual wrote: > >> > >> > >> On 11/08/2018 03:59 PM, Michal Hocko wrote: > >>> [Removing Wen Congyang and Tang Chen from the CC list because their > >>> emails bounce. It seems that we will never learn about their motivation] > >>> > >>> On Thu 08-11-18 11:04:13, Michal Hocko wrote: > >>>> From: Michal Hocko <mho...@suse.com> > >>>> > >>>> Per-cpu numa_node provides a default node for each possible cpu. The > >>>> association gets initialized during the boot when the architecture > >>>> specific code explores cpu->NUMA affinity. When the whole NUMA node is > >>>> removed though we are clearing this association > >>>> > >>>> try_offline_node > >>>> check_and_unmap_cpu_on_node > >>>> unmap_cpu_on_node > >>>> numa_clear_node > >>>> numa_set_node(cpu, NUMA_NO_NODE) > >>>> > >>>> This means that whoever calls cpu_to_node for a cpu associated with such > >>>> a node will get NUMA_NO_NODE. This is problematic for two reasons. First > >>>> it is fragile because __alloc_pages_node would simply blow up on an > >>>> out-of-bound access. We have encountered this when loading kvm module > >>>> BUG: unable to handle kernel paging request at 00000000000021c0 > >>>> IP: [<ffffffff8119ccb3>] __alloc_pages_nodemask+0x93/0xb70 > >>>> PGD 800000ffe853e067 PUD 7336bbc067 PMD 0 > >>>> Oops: 0000 [#1] SMP > >>>> [...] > >>>> CPU: 88 PID: 1223749 Comm: modprobe Tainted: G W > >>>> 4.4.156-94.64-default #1 > >>>> task: ffff88727eff1880 ti: ffff887354490000 task.ti: ffff887354490000 > >>>> RIP: 0010:[<ffffffff8119ccb3>] [<ffffffff8119ccb3>] > >>>> __alloc_pages_nodemask+0x93/0xb70 > >>>> RSP: 0018:ffff887354493b40 EFLAGS: 00010202 > >>>> RAX: 00000000000021c0 RBX: 0000000000000000 RCX: 0000000000000000 > >>>> RDX: 0000000000000000 RSI: 0000000000000002 RDI: 00000000014000c0 > >>>> RBP: 00000000014000c0 R08: ffffffffffffffff R09: 0000000000000000 > >>>> R10: ffff88fffc89e790 R11: 0000000000014000 R12: 0000000000000101 > >>>> R13: ffffffffa0772cd4 R14: ffffffffa0769ac0 R15: 0000000000000000 > >>>> FS: 00007fdf2f2f1700(0000) GS:ffff88fffc880000(0000) > >>>> knlGS:0000000000000000 > >>>> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > >>>> CR2: 00000000000021c0 CR3: 00000077205ee000 CR4: 0000000000360670 > >>>> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 > >>>> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 > >>>> Stack: > >>>> 0000000000000086 014000c014d20400 ffff887354493bb8 ffff882614d20f4c > >>>> 0000000000000000 0000000000000046 0000000000000046 ffffffff810ac0c9 > >>>> ffff88ffe78c0000 ffffffff0000009f ffffe8ffe82d3500 ffff88ff8ac55000 > >>>> Call Trace: > >>>> [<ffffffffa07476cd>] alloc_vmcs_cpu+0x3d/0x90 [kvm_intel] > >>>> [<ffffffffa0772c0c>] hardware_setup+0x781/0x849 [kvm_intel] > >>>> [<ffffffffa04a1c58>] kvm_arch_hardware_setup+0x28/0x190 [kvm] > >>>> [<ffffffffa04856fc>] kvm_init+0x7c/0x2d0 [kvm] > >>>> [<ffffffffa0772cf2>] vmx_init+0x1e/0x32c [kvm_intel] > >>>> [<ffffffff8100213a>] do_one_initcall+0xca/0x1f0 > >>>> [<ffffffff81193886>] do_init_module+0x5a/0x1d7 > >>>> [<ffffffff81112083>] load_module+0x1393/0x1c90 > >>>> [<ffffffff81112b30>] SYSC_finit_module+0x70/0xa0 > >>>> [<ffffffff8161cbc3>] entry_SYSCALL_64_fastpath+0x1e/0xb7 > >>>> DWARF2 unwinder stuck at entry_SYSCALL_64_fastpath+0x1e/0xb7 > >>>> > >>>> on an older kernel but the code is basically the same in the current > >>>> Linus tree as well. alloc_vmcs_cpu could use alloc_pages_nodemask which > >>>> would recognize NUMA_NO_NODE and use alloc_pages_node which would > >>>> translate > >>>> it to numa_mem_id but that is wrong as well because it would use a cpu > >>>> affinity of the local CPU which might be quite far from the original > >>>> node. > >> > >> But then the original node is getting/already off-lined. The allocation is > >> going to come from a different node. alloc_pages_node() at least steer the > >> allocation alway from VM_BUG_ON() because of NUMA_NO_NODE by replacing it > >> with numa_mem_id(). > >> > >> If node fallback order is important for this allocation then could not it > >> use __alloc_pages_nodemask() directly giving preference for its zonelist > >> node and nodemask. Just curious. > > > > How does the caller get the right node to allocate from? We do have the > > proper zone list for the offline node so why not use it? > I get your point. NODE_DATA() for the off lined node is still around and > so does the proper zone list for allocation, so why the caller should work > around the problem by building it's preferred nodemask_t etc. No problem, > I was just curious.
I thought I've made it cler in the changelog. If not, I am open to suggestions on how to make it more clear. -- Michal Hocko SUSE Labs
