linux-kernel - [PATCH v5 05/12] RISC-V: Disable preemption before enabling interrupts

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Date:   Thu, 13 Sep 2018 11:36:58 -0700
From:   Atish Patra <atish.patra@....com>
To:     palmer@...ive.com, linux-riscv@...ts.infradead.org,
        hch@...radead.org, anup@...infault.org
Cc:     mark.rutland@....com, atish.patra@....com, tglx@...utronix.de,
        linux-kernel@...r.kernel.org, Damien.LeMoal@....com,
        marc.zyngier@....com, jeremy.linton@....com,
        gregkh@...uxfoundation.org, jason@...edaemon.net,
        catalin.marinas@....com, dmitriy@...-tech.org,
        ard.biesheuvel@...aro.org, schwab@...ux-m68k.org
Subject: [PATCH v5 05/12] RISC-V: Disable preemption before enabling interrupts

Currently, irq is enabled before preemption disabling happens.
If the scheduler fired right here and cpu is scheduled then it
may blow up.

Signed-off-by: Palmer Dabbelt <palmer@...ive.com>
[Atish: Commit text and code comment formatting update]
Signed-off-by: Atish Patra <atish.patra@....com>
Reviewed-by: Christoph Hellwig <hch@....de>
---
 arch/riscv/kernel/smpboot.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/arch/riscv/kernel/smpboot.c b/arch/riscv/kernel/smpboot.c
index 712e9ca8..670749ec 100644
--- a/arch/riscv/kernel/smpboot.c
+++ b/arch/riscv/kernel/smpboot.c
@@ -111,7 +111,11 @@ asmlinkage void __init smp_callin(void)
 	 * 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);
 }
-- 
2.7.4