From: "Paul E. McKenney" <paulmck@kernel.org>
To: rcu@vger.kernel.org
Cc: linux-kernel@vger.kernel.org, kernel-team@fb.com,
rostedt@goodmis.org, "Paul E. McKenney" <paulmck@kernel.org>
Subject: [PATCH rcu 14/19] srcu: Explain srcu_funnel_gp_start() call to list_add() is safe
Date: Fri, 4 Feb 2022 15:38:57 -0800 [thread overview]
Message-ID: <20220204233902.1902-14-paulmck@kernel.org> (raw)
In-Reply-To: <20220204233858.GA1469@paulmck-ThinkPad-P17-Gen-1>
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!
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
kernel/rcu/srcutree.c | 6 ++++++
1 file changed, 6 insertions(+)
diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
index 39dc3015dfeba..d16104405c8f9 100644
--- a/kernel/rcu/srcutree.c
+++ b/kernel/rcu/srcutree.c
@@ -757,6 +757,12 @@ 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));
--
2.31.1.189.g2e36527f23
next prev parent reply other threads:[~2022-02-04 23:39 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-02-04 23:38 [PATCH rcu 0/19] SRCU updates for v5.18 Paul E. McKenney
2022-02-04 23:38 ` [PATCH rcu 01/19] srcu: Tighten cleanup_srcu_struct() GP checks Paul E. McKenney
2022-02-04 23:38 ` [PATCH rcu 02/19] srcu: Fix s/is/if/ typo in srcu_node comment Paul E. McKenney
2022-02-04 23:38 ` [PATCH rcu 03/19] srcu: Make srcu_funnel_gp_start() cache ->mynode in snp_leaf Paul E. McKenney
2022-02-04 23:38 ` [PATCH rcu 04/19] srcu: Dynamically allocate srcu_node array Paul E. McKenney
2022-02-04 23:38 ` [PATCH rcu 05/19] srcu: Make Tree SRCU able to operate without snp_node array Paul E. McKenney
2022-02-04 23:38 ` [PATCH rcu 06/19] srcu: Add size-state transitioning code Paul E. McKenney
2022-02-04 23:38 ` [PATCH rcu 07/19] srcu: Make rcutorture dump the SRCU size state Paul E. McKenney
2022-02-04 23:38 ` [PATCH rcu 08/19] srcu: Add boot-time control over srcu_node array allocation Paul E. McKenney
2022-02-04 23:38 ` [PATCH rcu 09/19] srcu: Use export for srcu_struct defined by DEFINE_STATIC_SRCU() Paul E. McKenney
2022-02-04 23:38 ` [PATCH rcu 10/19] srcu: Compute snp_seq earlier in srcu_funnel_gp_start() Paul E. McKenney
2022-02-04 23:38 ` [PATCH rcu 11/19] srcu: Use invalid initial value for srcu_node GP sequence numbers Paul E. McKenney
2022-02-04 23:38 ` [PATCH rcu 12/19] srcu: Avoid NULL dereference in srcu_torture_stats_print() Paul E. McKenney
2022-02-04 23:38 ` [PATCH rcu 13/19] srcu: Prevent cleanup_srcu_struct() from freeing non-dynamic ->sda Paul E. McKenney
2022-02-04 23:38 ` Paul E. McKenney [this message]
2022-02-04 23:38 ` [PATCH rcu 15/19] srcu: Create concurrency-safe helper for initiating size transition Paul E. McKenney
2022-02-04 23:38 ` [PATCH rcu 16/19] srcu: Add contention-triggered addition of srcu_node tree Paul E. McKenney
2022-02-04 23:39 ` [PATCH rcu 17/19] srcu: Make srcu_size_state_name static Paul E. McKenney
2022-02-04 23:39 ` [PATCH rcu 18/19] srcu: Automatically determine size-transition strategy at boot Paul E. McKenney
2022-02-04 23:39 ` [PATCH rcu 19/19] srcu: Add contention check to call_srcu() srcu_data ->lock acquisition Paul E. McKenney
[not found] ` <20220205030303.2408-1-hdanton@sina.com>
2022-02-05 5:20 ` Paul E. McKenney
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