srcu: Mark callbacks not currently participating in barrier operation

SRCU keeps a count of the number of callbacks that the current
srcu_barrier() is waiting on, but there is currently no easy way to
work out which callback is stuck.  One way to do this is to mark idle
SRCU-barrier callbacks by making the ->next pointer point to the callback
itself, and this commit does just that.

Later commits will use this for debug output.

Signed-off-by: "Paul E. McKenney" <paulmck@kernel.org>
Signed-off-by: Neeraj Upadhyay <neeraj.upadhyay@kernel.org>

diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
index aaee09a6748c2fcc05493a38d0adfb31900ed073..31706e3293bcee7ab75d2100899cb2f77ec207bd 100644 (file)
--- a/kernel/rcu/srcutree.c
+++ b/kernel/rcu/srcutree.c
@@ -137,6 +137,7 @@ static void init_srcu_struct_data(struct srcu_struct *ssp)
                sdp->srcu_cblist_invoking = false;
                sdp->srcu_gp_seq_needed = ssp->srcu_sup->srcu_gp_seq;
                sdp->srcu_gp_seq_needed_exp = ssp->srcu_sup->srcu_gp_seq;
+               sdp->srcu_barrier_head.next = &sdp->srcu_barrier_head;
                sdp->mynode = NULL;
                sdp->cpu = cpu;
                INIT_WORK(&sdp->work, srcu_invoke_callbacks);
@@ -1562,6 +1563,7 @@ static void srcu_barrier_cb(struct rcu_head *rhp)
        struct srcu_data *sdp;
        struct srcu_struct *ssp;
 
+       rhp->next = rhp; // Mark the callback as having been invoked.
        sdp = container_of(rhp, struct srcu_data, srcu_barrier_head);
        ssp = sdp->ssp;
        if (atomic_dec_and_test(&ssp->srcu_sup->srcu_barrier_cpu_cnt))