4.17-stable review patch. If anyone has any objections, please let me know.
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From: Nicholas Piggin npiggin@gmail.com
[ Upstream commit de6e5d38417e6cdb005843db420a2974993d36ff ]
Marking CPUs stopped by smp_send_stop as offline can cause warnings due to cross-CPU wakeups. This trace was noticed on a busy system running a sysrq+c crash test, after the injected crash:
WARNING: CPU: 51 PID: 1546 at kernel/sched/core.c:1179 set_task_cpu+0x22c/0x240 CPU: 51 PID: 1546 Comm: kworker/u352:1 Tainted: G D Workqueue: mlx5e mlx5e_update_stats_work [mlx5_core] [...] NIP [c00000000017c21c] set_task_cpu+0x22c/0x240 LR [c00000000017d580] try_to_wake_up+0x230/0x720 Call Trace: [c000000001017700] runqueues+0x0/0xb00 (unreliable) [c00000000017d580] try_to_wake_up+0x230/0x720 [c00000000015a214] insert_work+0x104/0x140 [c00000000015adb0] __queue_work+0x230/0x690 [c000003fc5007910] [c00000000015b26c] queue_work_on+0x5c/0x90 [c0080000135fc8f8] mlx5_cmd_exec+0x538/0xcb0 [mlx5_core] [c008000013608fd0] mlx5_core_access_reg+0x140/0x1d0 [mlx5_core] [c00800001362777c] mlx5e_update_pport_counters.constprop.59+0x6c/0x90 [mlx5_core] [c008000013628868] mlx5e_update_ndo_stats+0x28/0x90 [mlx5_core] [c008000013625558] mlx5e_update_stats_work+0x68/0xb0 [mlx5_core] [c00000000015bcec] process_one_work+0x1bc/0x5f0 [c00000000015ecac] worker_thread+0xac/0x6b0 [c000000000168338] kthread+0x168/0x1b0 [c00000000000b628] ret_from_kernel_thread+0x5c/0xb4
This happens because firstly the CPU is not really offline in the usual sense, processes and interrupts have not been migrated away. Secondly smp_send_stop does not happen atomically on all CPUs, so one CPU can have marked itself offline, while another CPU is still running processes or interrupts which can affect the first CPU.
Fix this by just not marking the CPU as offline. It's more like frozen in time, so offline does not really reflect its state properly anyway. There should be nothing in the crash/panic path that walks online CPUs and synchronously waits for them, so this change should not introduce new hangs.
Signed-off-by: Nicholas Piggin npiggin@gmail.com Signed-off-by: Michael Ellerman mpe@ellerman.id.au Signed-off-by: Sasha Levin alexander.levin@microsoft.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/powerpc/kernel/smp.c | 6 ------ 1 file changed, 6 deletions(-)
--- a/arch/powerpc/kernel/smp.c +++ b/arch/powerpc/kernel/smp.c @@ -579,9 +579,6 @@ static void nmi_stop_this_cpu(struct pt_ nmi_ipi_busy_count--; nmi_ipi_unlock();
- /* Remove this CPU */ - set_cpu_online(smp_processor_id(), false); - spin_begin(); while (1) spin_cpu_relax(); @@ -596,9 +593,6 @@ void smp_send_stop(void)
static void stop_this_cpu(void *dummy) { - /* Remove this CPU */ - set_cpu_online(smp_processor_id(), false); - hard_irq_disable(); spin_begin(); while (1)