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    SubjectRe: [PATCH RFC tip/core/rcu 1/2] srcu: Allow use of Tiny/Tree SRCU from both process and interrupt context
    On Mon, Jun 05, 2017 at 03:09:50PM -0700, Paul E. McKenney wrote:
    > diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
    > index 3ae8474557df..157654fa436a 100644
    > --- a/kernel/rcu/srcutree.c
    > +++ b/kernel/rcu/srcutree.c
    > @@ -357,7 +357,7 @@ EXPORT_SYMBOL_GPL(cleanup_srcu_struct);
    >
    > /*
    > * Counts the new reader in the appropriate per-CPU element of the
    > - * srcu_struct. Must be called from process context.
    > + * srcu_struct.
    > * Returns an index that must be passed to the matching srcu_read_unlock().
    > */
    > int __srcu_read_lock(struct srcu_struct *sp)
    > @@ -365,7 +365,7 @@ int __srcu_read_lock(struct srcu_struct *sp)
    > int idx;
    >
    > idx = READ_ONCE(sp->srcu_idx) & 0x1;
    > - __this_cpu_inc(sp->sda->srcu_lock_count[idx]);
    > + this_cpu_inc(sp->sda->srcu_lock_count[idx]);
    > smp_mb(); /* B */ /* Avoid leaking the critical section. */
    > return idx;
    > }

    So again, the change is to make this an IRQ safe operation, however if
    we have this balance requirement, the IRQ will not visibly change the
    value and load-store should be good again, no?

    Or am I missing some other detail with this implementation?

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