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srcu: Explain srcu_funnel_gp_start() call to list_add() is safe 

This commit adds a comment explaining why an unprotected call to
list_add() from srcu_funnel_gp_start() can be safe.  TL;DR: It is only
called during very early boot when we don't have no steeking concurrency!

Co-developed-by: Neeraj Upadhyay <quic_neeraju@quicinc.com>
Signed-off-by: Neeraj Upadhyay <quic_neeraju@quicinc.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit is contained in:
Paul E. McKenney 2022-01-27 13:47:42 -08:00
parent 46470cf85d
commit ee5e2448bc
1 changed files with 6 additions and 0 deletions
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6
kernel/rcu/srcutree.c
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@ -776,6 +776,12 @@ static void srcu_funnel_gp_start(struct srcu_struct *ssp, struct srcu_data *sdp,
rcu_seq_state(ssp->srcu_gp_seq) == SRCU_STATE_IDLE) {
WARN_ON_ONCE(ULONG_CMP_GE(ssp->srcu_gp_seq, ssp->srcu_gp_seq_needed));
srcu_gp_start(ssp);
// And how can that list_add() in the "else" clause
// possibly be safe for concurrent execution? Well,
// it isn't. And it does not have to be. After all, it
// can only be executed during early boot when there is only
// the one boot CPU running with interrupts still disabled.
if (likely(srcu_init_done))
queue_delayed_work(rcu_gp_wq, &ssp->work,
srcu_get_delay(ssp));