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    SubjectRe: [1/4] rcu: Detect uses of rcu read side in extended quiescent states
    On Mon, Jun 06, 2011 at 09:40:05PM -0700, Paul E. McKenney wrote:> 
    > The bit I am missing is how to distinguish between spinlocks (where
    > sleeping is illegal) and mutexes (where sleeping is perfectly fine).
    > We could teach lockdep the difference, I suppose, but it is not clear
    > to me that it is worth it.

    Ah, in fact it doesn't pass through any lockdep check.

    It's only a function called might_sleep() that is placed in functions
    that can sleep. And inside might_sleep() it checks whether it is in a preemptible
    area. So it's actually locking-agnostic, it only relies on the preempt_count
    and some more for the preempt rcu cases.

    I think it is called CONFIG_DEBUG_SPINLOCK_SLEEP because it was first used
    for spinlock debugging purposes. But then it has a broader use now: sleep
    inside preemptible section, sleep inside interrupts, sleep inside rcu.

    It certainly deserves a rename, like CONFIG_DEBUG_ILLEGAL_SLEEP.

    > In contrast, with RCU, this is straightforward -- check for rcu_sched
    > and rcu_bh, but not SRCU.
    > Thanx, Paul

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