Commit 99659f64 authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

srcu: Create concurrency-safe helper for initiating size transition 



Once there are contention-initiated size transitions, it will be
possible for rcutorture to initiate a transition at the same time
as a contention-initiated transition.  This commit therefore creates
a concurrency-safe helper function named srcu_transition_to_big() to
safely initiate size transitions.

Co-developed-by: default avatarNeeraj Upadhyay <quic_neeraju@quicinc.com>
Signed-off-by: default avatarNeeraj Upadhyay <quic_neeraju@quicinc.com>
Signed-off-by: default avatarPaul E. McKenney <paulmck@kernel.org>
parent ee5e2448

kernel/rcu/srcutree.c

+21 −2
Original line number Diff line number Diff line
@@ -272,6 +272,25 @@ EXPORT_SYMBOL_GPL(init_srcu_struct); 


#endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */



/*

 * Initiate an idempotent transition to SRCU_SIZE_BIG.

 */

static void srcu_transition_to_big(struct srcu_struct *ssp)

{

	unsigned long flags;



	/* Double-checked locking on ->srcu_size-state. */

	if (smp_load_acquire(&ssp->srcu_size_state) != SRCU_SIZE_SMALL)

		return;

	spin_lock_irqsave_rcu_node(ssp, flags);

	if (smp_load_acquire(&ssp->srcu_size_state) != SRCU_SIZE_SMALL) {

		spin_unlock_irqrestore_rcu_node(ssp, flags);

		return;

	}

	smp_store_release(&ssp->srcu_size_state, SRCU_SIZE_ALLOC);

	spin_unlock_irqrestore_rcu_node(ssp, flags);

}



/*

 * First-use initialization of statically allocated srcu_struct

 * structure.  Wiring up the combining tree is more than can be
@@ -1523,8 +1542,8 @@ void srcu_torture_stats_print(struct srcu_struct *ssp, char *tt, char *tf) 
		}

		pr_cont(" T(%ld,%ld)\n", s0, s1);

	}

	if (READ_ONCE(ssp->srcu_size_state) == SRCU_SIZE_SMALL && convert_to_big == 2)

		WRITE_ONCE(ssp->srcu_size_state, SRCU_SIZE_ALLOC);

	if (convert_to_big == 2)

		srcu_transition_to_big(ssp);

}

EXPORT_SYMBOL_GPL(srcu_torture_stats_print);