# git rev-parse -q --verify 801980f6497946048709b9b09771a1729551d705^{commit}
801980f6497946048709b9b09771a1729551d705
already have revision, skipping fetch
# git checkout -q -f -B kisskb 801980f6497946048709b9b09771a1729551d705
# git clean -qxdf
# < git log -1
# commit 801980f6497946048709b9b09771a1729551d705
# Author: Michael Roth <mdroth@linux.vnet.ibm.com>
# Date:   Tue Aug 11 11:15:44 2020 -0500
# 
#     powerpc/pseries/hotplug-cpu: wait indefinitely for vCPU death
#     
#     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
# < /opt/cross/kisskb/korg/gcc-4.9.4-nolibc/powerpc64-linux/bin/powerpc64-linux-gcc --version
# < /opt/cross/kisskb/korg/gcc-4.9.4-nolibc/powerpc64-linux/bin/powerpc64-linux-ld --version
# < git log --format=%s --max-count=1 801980f6497946048709b9b09771a1729551d705
# < make -s -j 48 ARCH=powerpc O=/kisskb/build/powerpc-fixes_40x_walnut_defconfig_powerpc-gcc4.9 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-4.9.4-nolibc/powerpc64-linux/bin/powerpc64-linux-  40x/walnut_defconfig
# < make -s -j 48 ARCH=powerpc O=/kisskb/build/powerpc-fixes_40x_walnut_defconfig_powerpc-gcc4.9 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-4.9.4-nolibc/powerpc64-linux/bin/powerpc64-linux-  help
# make -s -j 48 ARCH=powerpc O=/kisskb/build/powerpc-fixes_40x_walnut_defconfig_powerpc-gcc4.9 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-4.9.4-nolibc/powerpc64-linux/bin/powerpc64-linux-  olddefconfig
# make -s -j 48 ARCH=powerpc O=/kisskb/build/powerpc-fixes_40x_walnut_defconfig_powerpc-gcc4.9 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-4.9.4-nolibc/powerpc64-linux/bin/powerpc64-linux-  
/kisskb/src/block/genhd.c: In function 'diskstats_show':
/kisskb/src/block/genhd.c:1667:1: warning: the frame size of 1160 bytes is larger than 1024 bytes [-Wframe-larger-than=]
 }
 ^
Completed OK
# rm -rf /kisskb/build/powerpc-fixes_40x_walnut_defconfig_powerpc-gcc4.9
# Build took: 0:00:38.455061