From 610f01b9a88a9ef8b506709a825c17395c56a62a Mon Sep 17 00:00:00 2001 From: Stafford Horne Date: Fri, 3 Nov 2017 12:22:27 +0900 Subject: [PATCH] openrisc: fix possible deadlock scenario during timer sync OpenRISC borrows its timer sync logic from MIPS, Matt helped to review the OpenRISC implementation and noted that we may suffer the same deadlock case that MIPS has faced. The case being: "the MIPS timer synchronization code contained the possibility of deadlock. If you mark a CPU online before it goes into the synchronize loop, then the boot CPU can schedule a different thread and send IPIs to all "online" CPUs. It gets stuck waiting for the secondary to ack it's IPI, since this secondary CPU has not enabled IRQs yet, and is stuck waiting for the master to synchronise with it. The system then deadlocks." Fix this by moving set_cpu_online() to after timer sync. Reported-by: Matt Redfearn Signed-off-by: Stafford Horne --- arch/openrisc/kernel/smp.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/arch/openrisc/kernel/smp.c b/arch/openrisc/kernel/smp.c index 4d80ce6..7d518ee 100644 --- a/arch/openrisc/kernel/smp.c +++ b/arch/openrisc/kernel/smp.c @@ -127,10 +127,10 @@ asmlinkage __init void secondary_start_kernel(void) /* * OK, now it's safe to let the boot CPU continue */ - set_cpu_online(cpu, true); complete(&cpu_running); synchronise_count_slave(cpu); + set_cpu_online(cpu, true); local_irq_enable(); -- 2.7.4