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lockdep: Add CPU-idle/offline warning to lockdep-RCU splat

It is illegal to use RCU from a CPU that has reported idleness or
offlinedness to RCU.  However, it can be quite difficult to determine
from a stack trace whether or not a given CPU is idle or offline.
Therefore, this commit adds idle/offline diagnostics to the lockdep-RCU
error message.

Signed-off-by: Paul E. McKenney <>
Signed-off-by: Paul E. McKenney <>
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1 parent c0cfbbb commit c5fdcec927ee31fc96e92339c3a83ac6e0725289 Paul E. McKenney committed with paulmck Jan 30, 2012
Showing with 7 additions and 1 deletion.
  1. +7 −1 kernel/lockdep.c
8 kernel/lockdep.c
@@ -4176,7 +4176,13 @@ void lockdep_rcu_suspicious(const char *file, const int line, const char *s)
printk("%s:%d %s!\n", file, line, s);
printk("\nother info that might help us debug this:\n\n");
- printk("\nrcu_scheduler_active = %d, debug_locks = %d\n", rcu_scheduler_active, debug_locks);
+ printk("\n%srcu_scheduler_active = %d, debug_locks = %d\n",
+ !rcu_lockdep_current_cpu_online()
+ ? "RCU used illegally from offline CPU!\n"
+ : rcu_is_cpu_idle()
+ ? "RCU used illegally from idle CPU!\n"
+ : "",
+ rcu_scheduler_active, debug_locks);
* If a CPU is in the RCU-free window in idle (ie: in the section

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