From ff081e05bfba3461119cd280201d163b6858eda2 Mon Sep 17 00:00:00 2001 From: Stephen Boyd Date: Fri, 6 Jul 2012 22:03:42 +0100 Subject: ARM: 7457/1: smp: Fix suspicious RCU originating from cpu_die() 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: [] complete+0x1c/0x5c #1: (&p->pi_lock){-.-.-.}, at: [] try_to_wake_up+0x2c/0x388 #2: (&rq->lock){-.-.-.}, at: [] try_to_wake_up+0x130/0x388 #3: (rcu_read_lock){.+.+..}, at: [] cpuacct_charge+0x28/0x1f4 stack backtrace: [] (unwind_backtrace+0x0/0x12c) from [] (cpuacct_charge+0x94/0x1f4) [] (cpuacct_charge+0x94/0x1f4) from [] (update_curr+0x24c/0x2c8) [] (update_curr+0x24c/0x2c8) from [] (enqueue_task_fair+0x50/0x194) [] (enqueue_task_fair+0x50/0x194) from [] (enqueue_task+0x30/0x34) [] (enqueue_task+0x30/0x34) from [] (ttwu_activate+0x14/0x38) [] (ttwu_activate+0x14/0x38) from [] (try_to_wake_up+0x178/0x388) [] (try_to_wake_up+0x178/0x388) from [] (__wake_up_common+0x34/0x78) [] (__wake_up_common+0x34/0x78) from [] (complete+0x48/0x5c) [] (complete+0x48/0x5c) from [] (cpu_die+0x2c/0x58) [] (cpu_die+0x2c/0x58) from [] (cpu_idle+0x64/0xfc) [] (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 and eventually grabs an RCU read lock in cpuacct_charge(). Mark complete() as RCU_NONIDLE so that RCU pays attention to this CPU for the duration of the complete() function even though it's in idle. Suggested-by: "Paul E. McKenney" Signed-off-by: Stephen Boyd Signed-off-by: Russell King --- arch/arm/kernel/smp.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'arch/arm') diff --git a/arch/arm/kernel/smp.c b/arch/arm/kernel/smp.c index 2c7217d971db..aea74f5bc34a 100644 --- a/arch/arm/kernel/smp.c +++ b/arch/arm/kernel/smp.c @@ -179,7 +179,7 @@ void __ref cpu_die(void) mb(); /* Tell __cpu_die() that this CPU is now safe to dispose of */ - complete(&cpu_died); + RCU_NONIDLE(complete(&cpu_died)); /* * actual CPU shutdown procedure is at least platform (if not -- cgit v1.2.3