From: paulmck@kernel.org
To: rcu@vger.kernel.org
Cc: linux-kernel@vger.kernel.org, kernel-team@fb.com,
mingo@kernel.org, jiangshanlai@gmail.com,
akpm@linux-foundation.org, mathieu.desnoyers@efficios.com,
josh@joshtriplett.org, tglx@linutronix.de, peterz@infradead.org,
rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com,
fweisbec@gmail.com, oleg@redhat.com, joel@joelfernandes.org,
Frederic Weisbecker <frederic@kernel.org>,
Neeraj Upadhyay <neeraju@codeaurora.org>,
Boqun Feng <boqun.feng@gmail.com>,
"Paul E . McKenney" <paulmck@kernel.org>
Subject: [PATCH tip/core/rcu 05/12] rcu/nocb: Avoid confusing double write of rdp->nocb_cb_sleep
Date: Wed, 3 Mar 2021 16:23:04 -0800 [thread overview]
Message-ID: <20210304002311.23655-5-paulmck@kernel.org> (raw)
In-Reply-To: <20210304002225.GA23492@paulmck-ThinkPad-P72>
From: Frederic Weisbecker <frederic@kernel.org>
The nocb_cb_wait() function first sets the rdp->nocb_cb_sleep flag to
true by after invoking the callbacks, and then sets it back to false if
it finds more callbacks that are ready to invoke.
This is confusing and will become unsafe if this flag is ever read
locklessly. This commit therefore writes it only once, based on the
state after both callback invocation and checking.
Reported-by: Paul E. McKenney <paulmck@kernel.org>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Lai Jiangshan <jiangshanlai@gmail.com>
Cc: Joel Fernandes <joel@joelfernandes.org>
Cc: Neeraj Upadhyay <neeraju@codeaurora.org>
Cc: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
kernel/rcu/tree_plugin.h | 7 ++++---
1 file changed, 4 insertions(+), 3 deletions(-)
diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 9fd8588..6a7f77d 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -2230,6 +2230,7 @@ static void nocb_cb_wait(struct rcu_data *rdp)
unsigned long flags;
bool needwake_state = false;
bool needwake_gp = false;
+ bool can_sleep = true;
struct rcu_node *rnp = rdp->mynode;
local_irq_save(flags);
@@ -2253,8 +2254,6 @@ static void nocb_cb_wait(struct rcu_data *rdp)
raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */
}
- WRITE_ONCE(rdp->nocb_cb_sleep, true);
-
if (rcu_segcblist_test_flags(cblist, SEGCBLIST_OFFLOADED)) {
if (!rcu_segcblist_test_flags(cblist, SEGCBLIST_KTHREAD_CB)) {
rcu_segcblist_set_flags(cblist, SEGCBLIST_KTHREAD_CB);
@@ -2262,7 +2261,7 @@ static void nocb_cb_wait(struct rcu_data *rdp)
needwake_state = true;
}
if (rcu_segcblist_ready_cbs(cblist))
- WRITE_ONCE(rdp->nocb_cb_sleep, false);
+ can_sleep = false;
} else {
/*
* De-offloading. Clear our flag and notify the de-offload worker.
@@ -2275,6 +2274,8 @@ static void nocb_cb_wait(struct rcu_data *rdp)
needwake_state = true;
}
+ WRITE_ONCE(rdp->nocb_cb_sleep, can_sleep);
+
if (rdp->nocb_cb_sleep)
trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("CBSleep"));
--
2.9.5
next prev parent reply other threads:[~2021-03-04 1:08 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-04 0:22 [PATCH tip/core/rcu 0/12] NOCB updates for v5.13 Paul E. McKenney
2021-03-04 0:23 ` [PATCH tip/core/rcu 01/12] rcu/nocb: Detect unsafe checks for offloaded rdp paulmck
2021-03-04 0:23 ` [PATCH tip/core/rcu 02/12] timer: Report ignored local enqueue in nohz mode paulmck
2021-03-04 11:58 ` Rafael J. Wysocki
2021-03-04 20:06 ` Paul E. McKenney
2021-03-04 0:23 ` [PATCH tip/core/rcu 03/12] rcu/nocb: Comment the reason behind BH disablement on batch processing paulmck
2021-03-04 0:23 ` [PATCH tip/core/rcu 04/12] rcu/nocb: Forbid NOCB toggling on offline CPUs paulmck
2021-03-04 0:23 ` paulmck [this message]
2021-03-04 0:23 ` [PATCH tip/core/rcu 06/12] rcu/nocb: Only (re-)initialize segcblist when needed on CPU up paulmck
2021-03-04 0:23 ` [PATCH tip/core/rcu 07/12] rcu/nocb: Rename nocb_gp_update_state to nocb_gp_update_state_deoffloading paulmck
2021-03-04 0:23 ` [PATCH tip/core/rcu 08/12] rcu: Make nocb_nobypass_lim_per_jiffy static paulmck
2021-03-04 0:23 ` [PATCH tip/core/rcu 09/12] rcu/nocb: Fix missed nocb_timer requeue paulmck
2021-03-04 0:23 ` [PATCH tip/core/rcu 10/12] rcu/nocb: Disable bypass when CPU isn't completely offloaded paulmck
2021-03-04 0:23 ` [PATCH tip/core/rcu 11/12] rcu/nocb: Remove stale comment above rcu_segcblist_offload() paulmck
2021-03-04 0:23 ` [PATCH tip/core/rcu 12/12] rcu/nocb: Move trace_rcu_nocb_wake() calls outside nocb_lock when possible paulmck
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