Messages in this thread Patch in this message | | | From | Stephen Boyd <> | Subject | [PATCH] ARM: smp: Fix suspicious RCU originating from cpu_die() | Date | Thu, 5 Jul 2012 16:45:58 -0700 |
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While running hotplug tests I ran into this RCU splat
=============================== [ INFO: suspicious RCU usage. ] 3.4.0 #3275 Tainted: G W ------------------------------- include/linux/rcupdate.h:729 rcu_read_lock() used illegally while idle!
other info that might help us debug this:
RCU used illegally from idle CPU! rcu_scheduler_active = 1, debug_locks = 0 RCU used illegally from extended quiescent state! 4 locks held by swapper/2/0: #0: ((cpu_died).wait.lock){......}, at: [<c00ab128>] complete+0x1c/0x5c #1: (&p->pi_lock){-.-.-.}, at: [<c00b275c>] try_to_wake_up+0x2c/0x388 #2: (&rq->lock){-.-.-.}, at: [<c00b2860>] try_to_wake_up+0x130/0x388 #3: (rcu_read_lock){.+.+..}, at: [<c00abe5c>] cpuacct_charge+0x28/0x1f4
stack backtrace: [<c001521c>] (unwind_backtrace+0x0/0x12c) from [<c00abec8>] (cpuacct_charge+0x94/0x1f4) [<c00abec8>] (cpuacct_charge+0x94/0x1f4) from [<c00b395c>] (update_curr+0x24c/0x2c8) [<c00b395c>] (update_curr+0x24c/0x2c8) from [<c00b59c4>] (enqueue_task_fair+0x50/0x194) [<c00b59c4>] (enqueue_task_fair+0x50/0x194) from [<c00afea4>] (enqueue_task+0x30/0x34) [<c00afea4>] (enqueue_task+0x30/0x34) from [<c00b0908>] (ttwu_activate+0x14/0x38) [<c00b0908>] (ttwu_activate+0x14/0x38) from [<c00b28a8>] (try_to_wake_up+0x178/0x388) [<c00b28a8>] (try_to_wake_up+0x178/0x388) from [<c00a82a0>] (__wake_up_common+0x34/0x78) [<c00a82a0>] (__wake_up_common+0x34/0x78) from [<c00ab154>] (complete+0x48/0x5c) [<c00ab154>] (complete+0x48/0x5c) from [<c07db7cc>] (cpu_die+0x2c/0x58) [<c07db7cc>] (cpu_die+0x2c/0x58) from [<c000f954>] (cpu_idle+0x64/0xfc) [<c000f954>] (cpu_idle+0x64/0xfc) from [<80208160>] (0x80208160)
When a cpu is marked offline during its idle thread it calls cpu_die() during an RCU idle period. cpu_die() calls complete() to notify the killing process that the cpu has died. complete() calls into the scheduler code which sometimes grabs an RCU read lock in cpuacct_charge().
To avoid this problem, copy what x86 is doing and have a per_cpu variable to track the cpu state and have the killing process poll that variable.
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> Signed-off-by: Stephen Boyd <sboyd@codeaurora.org> --- arch/arm/kernel/smp.c | 26 ++++++++++++++++---------- 1 file changed, 16 insertions(+), 10 deletions(-)
diff --git a/arch/arm/kernel/smp.c b/arch/arm/kernel/smp.c index 2c7217d..5430ea4 100644 --- a/arch/arm/kernel/smp.c +++ b/arch/arm/kernel/smp.c @@ -59,6 +59,7 @@ enum ipi_msg_type { }; static DECLARE_COMPLETION(cpu_running); +static DEFINE_PER_CPU(int, cpu_state) = { 0 }; int __cpuinit __cpu_up(unsigned int cpu, struct task_struct *idle) { @@ -143,22 +144,26 @@ int __cpu_disable(void) return 0; } -static DECLARE_COMPLETION(cpu_died); - /* * called on the thread which is asking for a CPU to be shutdown - * waits until shutdown has completed, or it is timed out. */ void __cpu_die(unsigned int cpu) { - if (!wait_for_completion_timeout(&cpu_died, msecs_to_jiffies(5000))) { - pr_err("CPU%u: cpu didn't die\n", cpu); - return; + unsigned int i; + + for (i = 0; i < 50; i++) { + if (per_cpu(cpu_state, cpu) == CPU_DEAD) { + if (platform_cpu_kill(cpu)) { + pr_notice("CPU%u: shutdown\n", cpu); + return; + } else { + break; + } + } + msleep(100); } - printk(KERN_NOTICE "CPU%u: shutdown\n", cpu); - - if (!platform_cpu_kill(cpu)) - printk("CPU%u: unable to kill\n", cpu); + pr_err("CPU%u: unable to kill\n", cpu); } /* @@ -179,7 +184,7 @@ void __ref cpu_die(void) mb(); /* Tell __cpu_die() that this CPU is now safe to dispose of */ - complete(&cpu_died); + __this_cpu_write(cpu_state, CPU_DEAD); /* * actual CPU shutdown procedure is at least platform (if not @@ -258,6 +263,7 @@ asmlinkage void __cpuinit secondary_start_kernel(void) * before we continue - which happens after __cpu_up returns. */ set_cpu_online(cpu, true); + per_cpu(cpu_state, smp_processor_id()) = CPU_ONLINE; complete(&cpu_running); /* -- Sent by an employee of the Qualcomm Innovation Center, Inc. The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.
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