From: "Paul E. McKenney" <>

Ever since cdf7abc4610a ("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

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 <>
 kernel/rcu/srcutree.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
index a8846ed7f352..60f3236beaf7 100644
--- a/kernel/rcu/srcutree.c
+++ b/kernel/rcu/srcutree.c
@@ -858,6 +858,7 @@ void __call_srcu(struct srcu_struct *sp, struct rcu_head 
                 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->func = func;
+       idx = srcu_read_lock(sp);
        sdp = this_cpu_ptr(sp->sda);
@@ -892,6 +894,7 @@ void __call_srcu(struct srcu_struct *sp, struct rcu_head 
                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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