From: Michael Roth mdroth@linux.vnet.ibm.com
[ Upstream commit 801980f6497946048709b9b09771a1729551d705 ]
For a power9 KVM guest with XIVE enabled, running a test loop where we hotplug 384 vcpus and then unplug them, the following traces can be seen (generally within a few loops) either from the unplugged vcpu:
cpu 65 (hwid 65) Ready to die... Querying DEAD? cpu 66 (66) shows 2 list_del corruption. next->prev should be c00a000002470208, but was c00a000002470048 ------------[ cut here ]------------ kernel BUG at lib/list_debug.c:56! Oops: Exception in kernel mode, sig: 5 [#1] LE SMP NR_CPUS=2048 NUMA pSeries Modules linked in: fuse nft_fib_inet nft_fib_ipv4 nft_fib_ipv6 ... CPU: 66 PID: 0 Comm: swapper/66 Kdump: loaded Not tainted 4.18.0-221.el8.ppc64le #1 NIP: c0000000007ab50c LR: c0000000007ab508 CTR: 00000000000003ac REGS: c0000009e5a17840 TRAP: 0700 Not tainted (4.18.0-221.el8.ppc64le) MSR: 800000000282b033 <SF,VEC,VSX,EE,FP,ME,IR,DR,RI,LE> CR: 28000842 XER: 20040000 ... NIP __list_del_entry_valid+0xac/0x100 LR __list_del_entry_valid+0xa8/0x100 Call Trace: __list_del_entry_valid+0xa8/0x100 (unreliable) free_pcppages_bulk+0x1f8/0x940 free_unref_page+0xd0/0x100 xive_spapr_cleanup_queue+0x148/0x1b0 xive_teardown_cpu+0x1bc/0x240 pseries_mach_cpu_die+0x78/0x2f0 cpu_die+0x48/0x70 arch_cpu_idle_dead+0x20/0x40 do_idle+0x2f4/0x4c0 cpu_startup_entry+0x38/0x40 start_secondary+0x7bc/0x8f0 start_secondary_prolog+0x10/0x14
or on the worker thread handling the unplug:
pseries-hotplug-cpu: Attempting to remove CPU <NULL>, drc index: 1000013a Querying DEAD? cpu 314 (314) shows 2 BUG: Bad page state in process kworker/u768:3 pfn:95de1 cpu 314 (hwid 314) Ready to die... page:c00a000002577840 refcount:0 mapcount:-128 mapping:0000000000000000 index:0x0 flags: 0x5ffffc00000000() raw: 005ffffc00000000 5deadbeef0000100 5deadbeef0000200 0000000000000000 raw: 0000000000000000 0000000000000000 00000000ffffff7f 0000000000000000 page dumped because: nonzero mapcount Modules linked in: kvm xt_CHECKSUM ipt_MASQUERADE xt_conntrack ... CPU: 0 PID: 548 Comm: kworker/u768:3 Kdump: loaded Not tainted 4.18.0-224.el8.bz1856588.ppc64le #1 Workqueue: pseries hotplug workque pseries_hp_work_fn Call Trace: dump_stack+0xb0/0xf4 (unreliable) bad_page+0x12c/0x1b0 free_pcppages_bulk+0x5bc/0x940 page_alloc_cpu_dead+0x118/0x120 cpuhp_invoke_callback.constprop.5+0xb8/0x760 _cpu_down+0x188/0x340 cpu_down+0x5c/0xa0 cpu_subsys_offline+0x24/0x40 device_offline+0xf0/0x130 dlpar_offline_cpu+0x1c4/0x2a0 dlpar_cpu_remove+0xb8/0x190 dlpar_cpu_remove_by_index+0x12c/0x150 dlpar_cpu+0x94/0x800 pseries_hp_work_fn+0x128/0x1e0 process_one_work+0x304/0x5d0 worker_thread+0xcc/0x7a0 kthread+0x1ac/0x1c0 ret_from_kernel_thread+0x5c/0x80
The latter trace is due to the following sequence:
page_alloc_cpu_dead drain_pages drain_pages_zone free_pcppages_bulk
where drain_pages() in this case is called under the assumption that the unplugged cpu is no longer executing. To ensure that is the case, and early call is made to __cpu_die()->pseries_cpu_die(), which runs a loop that waits for the cpu to reach a halted state by polling its status via query-cpu-stopped-state RTAS calls. It only polls for 25 iterations before giving up, however, and in the trace above this results in the following being printed only .1 seconds after the hotplug worker thread begins processing the unplug request:
pseries-hotplug-cpu: Attempting to remove CPU <NULL>, drc index: 1000013a Querying DEAD? cpu 314 (314) shows 2
At that point the worker thread assumes the unplugged CPU is in some unknown/dead state and procedes with the cleanup, causing the race with the XIVE cleanup code executed by the unplugged CPU.
Fix this by waiting indefinitely, but also making an effort to avoid spurious lockup messages by allowing for rescheduling after polling the CPU status and printing a warning if we wait for longer than 120s.
Fixes: eac1e731b59ee ("powerpc/xive: guest exploitation of the XIVE interrupt controller") Suggested-by: Michael Ellerman mpe@ellerman.id.au Signed-off-by: Michael Roth mdroth@linux.vnet.ibm.com Tested-by: Greg Kurz groug@kaod.org Reviewed-by: Thiago Jung Bauermann bauerman@linux.ibm.com Reviewed-by: Greg Kurz groug@kaod.org [mpe: Trim oopses in change log slightly for readability] Signed-off-by: Michael Ellerman mpe@ellerman.id.au Link: https://lore.kernel.org/r/20200811161544.10513-1-mdroth@linux.vnet.ibm.com Signed-off-by: Sasha Levin sashal@kernel.org --- arch/powerpc/platforms/pseries/hotplug-cpu.c | 18 ++++++++++++------ 1 file changed, 12 insertions(+), 6 deletions(-)
diff --git a/arch/powerpc/platforms/pseries/hotplug-cpu.c b/arch/powerpc/platforms/pseries/hotplug-cpu.c index 6d4ee03d476a9..ec04fc7f5a641 100644 --- a/arch/powerpc/platforms/pseries/hotplug-cpu.c +++ b/arch/powerpc/platforms/pseries/hotplug-cpu.c @@ -107,22 +107,28 @@ static int pseries_cpu_disable(void) */ static void pseries_cpu_die(unsigned int cpu) { - int tries; int cpu_status = 1; unsigned int pcpu = get_hard_smp_processor_id(cpu); + unsigned long timeout = jiffies + msecs_to_jiffies(120000);
- for (tries = 0; tries < 25; tries++) { + while (true) { cpu_status = smp_query_cpu_stopped(pcpu); if (cpu_status == QCSS_STOPPED || cpu_status == QCSS_HARDWARE_ERROR) break; - cpu_relax();
+ if (time_after(jiffies, timeout)) { + pr_warn("CPU %i (hwid %i) didn't die after 120 seconds\n", + cpu, pcpu); + timeout = jiffies + msecs_to_jiffies(120000); + } + + cond_resched(); }
- if (cpu_status != 0) { - printk("Querying DEAD? cpu %i (%i) shows %i\n", - cpu, pcpu, cpu_status); + if (cpu_status == QCSS_HARDWARE_ERROR) { + pr_warn("CPU %i (hwid %i) reported error while dying\n", + cpu, pcpu); }
/* Isolation and deallocation are definitely done by