Commit 0607ba84 authored Apr 25, 2018 by Paul E. McKenney Committed by Paul E. McKenney Nov 08, 2018

srcu: Prevent __call_srcu() counter wrap with read-side critical section



Ever since cdf7abc4 ("srcu: Allow use of Tiny/Tree SRCU from
both process and interrupt context"), it has been permissible
to use SRCU read-side critical sections in interrupt context.
This allows __call_srcu() to use SRCU read-side critical sections to
prevent a new SRCU grace period from ending before the call to either
srcu_funnel_gp_start() or srcu_funnel_exp_start completes, thus preventing
SRCU grace-period counter overflow during that time.

Note that this does not permit removal of the counter-wrap checks in
srcu_gp_end().  These check are necessary to handle the case where
a given CPU does not interact at all with SRCU for an extended time
period.

This commit therefore adds an SRCU read-side critical section to
__call_srcu() in order to prevent grace period counter wrap during
the funnel-locking process.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

parent f3e763c3

kernel/rcu/srcutree.c

+3 −0

Original line number	Diff line number	Diff line
		@@ -858,6 +858,7 @@ void __call_srcu(struct srcu_struct sp, struct rcu_head rhp,
		rcu_callback_t func, bool do_norm)
		{
		unsigned long flags;
		int idx;
		bool needexp = false;
		bool needgp = false;
		unsigned long s;
		@@ -871,6 +872,7 @@ void __call_srcu(struct srcu_struct sp, struct rcu_head rhp,
		return;
		}
		rhp->func = func;
		idx = srcu_read_lock(sp);
		local_irq_save(flags);
		sdp = this_cpu_ptr(sp->sda);
		spin_lock_rcu_node(sdp);
		@@ -892,6 +894,7 @@ void __call_srcu(struct srcu_struct sp, struct rcu_head rhp,
		srcu_funnel_gp_start(sp, sdp, s, do_norm);
		else if (needexp)
		srcu_funnel_exp_start(sp, sdp->mynode, s);
		srcu_read_unlock(sp, idx);
		}

		/**

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