From: "Paul E. McKenney" <paulmck@linux.ibm.com>
To: rcu@vger.kernel.org
Cc: linux-kernel@vger.kernel.org, mingo@kernel.org,
jiangshanlai@gmail.com, dipankar@in.ibm.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,
"Paul E. McKenney" <paulmck@linux.ibm.com>
Subject: [PATCH tip/core/rcu 08/18] rcu/nocb: Allow lockless use of rcu_segcblist_empty()
Date: Thu, 1 Aug 2019 16:08:00 -0700 [thread overview]
Message-ID: <20190801230810.21570-8-paulmck@linux.ibm.com> (raw)
In-Reply-To: <20190801230744.GA19115@linux.ibm.com>
Currently, rcu_segcblist_empty() assumes that the callback list is not
being changed by other CPUs, but upcoming changes will require it to
operate locklessly. This commit therefore adds the needed READ_ONCE()
call, along with the WRITE_ONCE() calls when updating the callback list's
->head field.
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
---
kernel/rcu/rcu_segcblist.c | 4 ++--
kernel/rcu/rcu_segcblist.h | 2 +-
2 files changed, 3 insertions(+), 3 deletions(-)
diff --git a/kernel/rcu/rcu_segcblist.c b/kernel/rcu/rcu_segcblist.c
index 0e7fe678b6ac..06435a368be5 100644
--- a/kernel/rcu/rcu_segcblist.c
+++ b/kernel/rcu/rcu_segcblist.c
@@ -213,7 +213,7 @@ void rcu_segcblist_extract_done_cbs(struct rcu_segcblist *rsclp,
if (!rcu_segcblist_ready_cbs(rsclp))
return; /* Nothing to do. */
*rclp->tail = rsclp->head;
- rsclp->head = *rsclp->tails[RCU_DONE_TAIL];
+ WRITE_ONCE(rsclp->head, *rsclp->tails[RCU_DONE_TAIL]);
WRITE_ONCE(*rsclp->tails[RCU_DONE_TAIL], NULL);
rclp->tail = rsclp->tails[RCU_DONE_TAIL];
for (i = RCU_CBLIST_NSEGS - 1; i >= RCU_DONE_TAIL; i--)
@@ -268,7 +268,7 @@ void rcu_segcblist_insert_done_cbs(struct rcu_segcblist *rsclp,
if (!rclp->head)
return; /* No callbacks to move. */
*rclp->tail = rsclp->head;
- rsclp->head = rclp->head;
+ WRITE_ONCE(rsclp->head, rclp->head);
for (i = RCU_DONE_TAIL; i < RCU_CBLIST_NSEGS; i++)
if (&rsclp->head == rsclp->tails[i])
WRITE_ONCE(rsclp->tails[i], rclp->tail);
diff --git a/kernel/rcu/rcu_segcblist.h b/kernel/rcu/rcu_segcblist.h
index f74960f0305c..d9142b3590a8 100644
--- a/kernel/rcu/rcu_segcblist.h
+++ b/kernel/rcu/rcu_segcblist.h
@@ -36,7 +36,7 @@ struct rcu_head *rcu_cblist_dequeue(struct rcu_cblist *rclp);
*/
static inline bool rcu_segcblist_empty(struct rcu_segcblist *rsclp)
{
- return !rsclp->head;
+ return !READ_ONCE(rsclp->head);
}
/* Return number of callbacks in segmented callback list. */
--
2.17.1
next prev parent reply other threads:[~2019-08-01 23:08 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-01 23:07 [PATCH tip/core/rcu 0/18] No-CBs cblist updates for v5.3-rc2 Paul E. McKenney
2019-08-01 23:07 ` [PATCH tip/core/rcu 01/18] rcu/nocb: Use separate flag to indicate disabled ->cblist Paul E. McKenney
2019-08-01 23:07 ` [PATCH tip/core/rcu 02/18] rcu/nocb: Use separate flag to indicate offloaded ->cblist Paul E. McKenney
2019-08-01 23:07 ` [PATCH tip/core/rcu 03/18] rcu/nocb: Add checks for offloaded callback processing Paul E. McKenney
2019-08-01 23:07 ` [PATCH tip/core/rcu 04/18] rcu/nocb: Make rcutree_migrate_callbacks() start at leaf rcu_node structure Paul E. McKenney
2019-08-01 23:07 ` [PATCH tip/core/rcu 05/18] rcu/nocb: Check for deferred nocb wakeups before nohz_full early exit Paul E. McKenney
2019-08-01 23:07 ` [PATCH tip/core/rcu 06/18] rcu/nocb: Remove deferred wakeup checks for extended quiescent states Paul E. McKenney
2019-08-01 23:07 ` [PATCH tip/core/rcu 07/18] rcu/nocb: Allow lockless use of rcu_segcblist_restempty() Paul E. McKenney
2019-08-01 23:08 ` Paul E. McKenney [this message]
2019-08-01 23:08 ` [PATCH tip/core/rcu 09/18] rcu/nocb: Leave ->cblist enabled for no-CBs CPUs Paul E. McKenney
2019-08-01 23:08 ` [PATCH tip/core/rcu 10/18] rcu/nocb: Use rcu_segcblist " Paul E. McKenney
2019-08-01 23:08 ` [PATCH tip/core/rcu 11/18] rcu/nocb: Remove obsolete nocb_head and nocb_tail fields Paul E. McKenney
2019-08-01 23:08 ` [PATCH tip/core/rcu 12/18] rcu/nocb: Remove obsolete nocb_q_count and nocb_q_count_lazy fields Paul E. McKenney
2019-08-01 23:08 ` [PATCH tip/core/rcu 13/18] rcu/nocb: Remove obsolete nocb_cb_tail and nocb_cb_head fields Paul E. McKenney
2019-08-01 23:08 ` [PATCH tip/core/rcu 14/18] rcu/nocb: Remove obsolete nocb_gp_head and nocb_gp_tail fields Paul E. McKenney
2019-08-01 23:08 ` [PATCH tip/core/rcu 15/18] rcu/nocb: Use build-time no-CBs check in rcu_do_batch() Paul E. McKenney
2019-08-01 23:08 ` [PATCH tip/core/rcu 16/18] rcu/nocb: Use build-time no-CBs check in rcu_core() Paul E. McKenney
2019-08-01 23:08 ` [PATCH tip/core/rcu 17/18] rcu/nocb: Use build-time no-CBs check in rcu_pending() Paul E. McKenney
2019-08-01 23:08 ` [PATCH tip/core/rcu 18/18] rcu/nocb: Suppress uninitialized false-positive in nocb_gp_wait() Paul E. McKenney
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20190801230810.21570-8-paulmck@linux.ibm.com \
--to=paulmck@linux.ibm.com \
--cc=akpm@linux-foundation.org \
--cc=dhowells@redhat.com \
--cc=dipankar@in.ibm.com \
--cc=edumazet@google.com \
--cc=fweisbec@gmail.com \
--cc=jiangshanlai@gmail.com \
--cc=joel@joelfernandes.org \
--cc=josh@joshtriplett.org \
--cc=linux-kernel@vger.kernel.org \
--cc=mathieu.desnoyers@efficios.com \
--cc=mingo@kernel.org \
--cc=oleg@redhat.com \
--cc=peterz@infradead.org \
--cc=rcu@vger.kernel.org \
--cc=rostedt@goodmis.org \
--cc=tglx@linutronix.de \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).