From mboxrd@z Thu Jan 1 00:00:00 1970 From: jason77.wang@gmail.com (Hui Wang) Date: Mon, 21 May 2012 17:45:31 +0800 Subject: [PATCH 2/2] ARM: SMP: use per cpu state to replace In-Reply-To: <1337593531-16191-2-git-send-email-jason77.wang@gmail.com> References: <1337593531-16191-1-git-send-email-jason77.wang@gmail.com> <1337593531-16191-2-git-send-email-jason77.wang@gmail.com> Message-ID: <1337593531-16191-3-git-send-email-jason77.wang@gmail.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org CPU hotplug will bring following call trace in the RT kernel: BUG: sleeping function called from invalid context at linux/kernel/rtmutex.c:707 pcnt: 1 0 in_atomic(): 1, irqs_disabled(): 128, pid: 0, name: swapper [<800413a0>] (unwind_backtrace+0x0/0xe4) from [<804ff214>] (rt_spin_lock+0x30/0x5c) [<804ff214>] (rt_spin_lock+0x30/0x5c) from [<8005a848>] (complete+0x1c/0x54) [<8005a848>] (complete+0x1c/0x54) from [<804f59f8>] (cpu_die+0x34/0x70) [<804f59f8>] (cpu_die+0x34/0x70) from [<8003b840>] (cpu_idle+0x54/0xd8) [<8003b840>] (cpu_idle+0x54/0xd8) from [<104f9ecc>] (0x104f9ecc) To avoid this call trace, we use per cpu variable to replace completion, and it is safe for this modification since all reference of per cpu_state variable is in the preempt disabled context. Signed-off-by: Hui Wang --- arch/arm/kernel/smp.c | 23 ++++++++++++++++++----- 1 files changed, 18 insertions(+), 5 deletions(-) diff --git a/arch/arm/kernel/smp.c b/arch/arm/kernel/smp.c index 05fed61..c63e2ff 100644 --- a/arch/arm/kernel/smp.c +++ b/arch/arm/kernel/smp.c @@ -122,6 +122,9 @@ int __cpuinit __cpu_up(unsigned int cpu) } #ifdef CONFIG_HOTPLUG_CPU +/* State of each CPU during hotplug phases */ +DEFINE_PER_CPU(int, cpu_state) = { 0 }; + static void percpu_timer_stop(void); /* @@ -171,6 +174,7 @@ static DECLARE_COMPLETION(cpu_died); void __cpu_die(unsigned int cpu) { struct task_struct *p; + unsigned long timeout; read_lock(&tasklist_lock); for_each_process(p) { @@ -179,10 +183,16 @@ void __cpu_die(unsigned int cpu) } read_unlock(&tasklist_lock); - if (!wait_for_completion_timeout(&cpu_died, msecs_to_jiffies(5000))) { - pr_err("CPU%u: cpu didn't die\n", cpu); - return; - } + timeout = jiffies + msecs_to_jiffies(5000); + + while (per_cpu(cpu_state, cpu) != CPU_DEAD) { + if (time_after(jiffies, timeout)) { + pr_err("CPU%u: cpu didn't die\n", cpu); + return; + } + cpu_relax(); + } + printk(KERN_NOTICE "CPU%u: shutdown\n", cpu); if (!platform_cpu_kill(cpu)) @@ -207,7 +217,7 @@ void __ref cpu_die(void) mb(); /* Tell __cpu_die() that this CPU is now safe to dispose of */ - complete(&cpu_died); + per_cpu(cpu_state, cpu) = CPU_DEAD; /* * actual CPU shutdown procedure is at least platform (if not @@ -285,6 +295,9 @@ asmlinkage void __cpuinit secondary_start_kernel(void) * the CPU migration code to notice that the CPU is online * before we continue - which happens after __cpu_up returns. */ +#ifdef CONFIG_HOTPLUG_CPU + per_cpu(cpu_state, cpu) = CPU_ONLINE; +#endif set_cpu_online(cpu, true); complete(&cpu_running); -- 1.7.6