linux-kernel - [PATCH 8/8] RISC-V: Disable preemption before enabling interrupts when booting secondary harts

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Date:   Mon, 27 Aug 2018 11:42:43 -0700
From:   Palmer Dabbelt <palmer@...ive.com>
To:      linux-riscv@...ts.infradead.org
Cc:     Palmer Dabbelt <palmer@...ive.com>, aou@...s.berkeley.edu,
        daniel.lezcano@...aro.org, tglx@...utronix.de,
        jason@...edaemon.net, marc.zyngier@....com, atish.patra@....com,
        dmitriy@...-tech.org, catalin.marinas@....com,
        ard.biesheuvel@...aro.org, Greg KH <gregkh@...uxfoundation.org>,
        jeremy.linton@....com, linux-riscv@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH 8/8] RISC-V: Disable preemption before enabling interrupts when booting secondary harts

I'm not sure, but I think this was a bug: if the scheduler fired right
here then I believe it would blow up.

Signed-off-by: Palmer Dabbelt <palmer@...ive.com>
---
 arch/riscv/kernel/smpboot.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/arch/riscv/kernel/smpboot.c b/arch/riscv/kernel/smpboot.c
index 953bc540207d..45515cc70181 100644
--- a/arch/riscv/kernel/smpboot.c
+++ b/arch/riscv/kernel/smpboot.c
@@ -110,7 +110,9 @@ asmlinkage void __init smp_callin(void)
 	/* Remote TLB flushes are ignored while the CPU is offline, so emit a local
 	 * TLB flush right now just in case. */
 	local_flush_tlb_all();
-	local_irq_enable();
+	/* Disable preemption before enabling interrupts, so we don't try to
+	 * schedule a CPU that hasn't actually started yet. */
 	preempt_disable();
+	local_irq_enable();
 	cpu_startup_entry(CPUHP_AP_ONLINE_IDLE);
 }
-- 
2.16.4