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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 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" <paulmck@linux.vnet.ibm.com> Signed-off-by: Stephen Boyd <sboyd@codeaurora.org> Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk> |
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