Documentation/RCU/lockdep-splat.rst

4 Lockdep-RCU Splat
7 Lockdep-RCU was added to the Linux kernel in early 2010
9 misuses of the RCU API, most notably using one of the rcu_dereference()
10 family to access an RCU-protected pointer without the proper protection.
11 When such misuse is detected, an lockdep-RCU splat is emitted.
13 The usual cause of a lockdep-RCU splat is someone accessing an
14 RCU-protected data structure without either (1) being in the right kind of
15 RCU read-side critical section or (2) holding the right update-side lock.
20 So let's look at an example RCU lockdep splat from 3.0-rc5, one that
24     WARNING: suspicious RCU usage
72 This form says that it must be in a plain vanilla RCU read-side critical
74 case.  Instead, we hold three locks, one of which might be RCU related.
76 is to inform RCU, perhaps by changing __cfq_exit_single_io_context() to
83 With this change, there would be no lockdep-RCU splat emitted if this
84 code was invoked either from within an RCU read-side critical section
86 the above lockdep-RCU splat because ->queue_lock is held (see #2 in the
89 On the other hand, perhaps we really do need an RCU read-side critical
103 With this change, the rcu_dereference() is always within an RCU
105 above lockdep-RCU splat.
115 this change would also suppress the above lockdep-RCU splat.