linux-kernel - [PATCH 1/3] RISC-V: Do not wait indefinitely in __cpu

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Message-Id: <1545865741-22795-2-git-send-email-atish.patra@wdc.com>
Date:   Wed, 26 Dec 2018 15:08:59 -0800
From:   Atish Patra <atish.patra@....com>
To:     linux-riscv@...ts.infradead.org
Cc:     Atish Patra <atish.patra@....com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Anup Patel <anup@...infault.org>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Dmitriy Cherkasov <dmitriy@...-tech.org>,
        Jason Cooper <jason@...edaemon.net>,
        linux-kernel@...r.kernel.org, Marc Zyngier <marc.zyngier@....com>,
        Michael Clark <michaeljclark@....com>,
        Palmer Dabbelt <palmer@...ive.com>,
        Patrick Stählin <me@...ki.ch>,
        Rob Herring <robh@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Damien Le Moal <Damien.LeMoal@....com>
Subject: [PATCH 1/3] RISC-V: Do not wait indefinitely in __cpu_up

In SMP path, __cpu_up waits for other CPU to come online
indefinitely. This is wrong as other CPU might be disabled
in machine mode and possible CPU is set to the cpus present
in DT.

Introduce a completion variable and waits only for a second.

Signed-off-by: Atish Patra <atish.patra@....com>
---
 arch/riscv/kernel/smpboot.c | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/arch/riscv/kernel/smpboot.c b/arch/riscv/kernel/smpboot.c
index 18cda0e8..bb8cd242 100644
--- a/arch/riscv/kernel/smpboot.c
+++ b/arch/riscv/kernel/smpboot.c
@@ -39,6 +39,7 @@
 
 void *__cpu_up_stack_pointer[NR_CPUS];
 void *__cpu_up_task_pointer[NR_CPUS];
+static DECLARE_COMPLETION(cpu_running);
 
 void __init smp_prepare_boot_cpu(void)
 {
@@ -77,6 +78,7 @@ void __init setup_smp(void)
 
 int __cpu_up(unsigned int cpu, struct task_struct *tidle)
 {
+	int ret = 0;
 	int hartid = cpuid_to_hartid_map(cpu);
 	tidle->thread_info.cpu = cpu;
 
@@ -92,10 +94,15 @@ int __cpu_up(unsigned int cpu, struct task_struct *tidle)
 		  task_stack_page(tidle) + THREAD_SIZE);
 	WRITE_ONCE(__cpu_up_task_pointer[hartid], tidle);
 
-	while (!cpu_online(cpu))
-		cpu_relax();
+	wait_for_completion_timeout(&cpu_running,
+					    msecs_to_jiffies(1000));
 
-	return 0;
+	if (!cpu_online(cpu)) {
+		pr_crit("CPU%u: failed to come online\n", cpu);
+		ret = -EIO;
+	}
+
+	return ret;
 }
 
 void __init smp_cpus_done(unsigned int max_cpus)
@@ -121,6 +128,7 @@ asmlinkage void __init smp_callin(void)
 	 * a local TLB flush right now just in case.
 	 */
 	local_flush_tlb_all();
+	complete(&cpu_running);
 	/*
 	 * Disable preemption before enabling interrupts, so we don't try to
 	 * schedule a CPU that hasn't actually started yet.
-- 
2.7.4