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 07/18] rcu/nocb: Allow lockless use of rcu_segcblist_restempty()
Date: Thu, 1 Aug 2019 16:07:59 -0700 [thread overview]
Message-ID: <20190801230810.21570-7-paulmck@linux.ibm.com> (raw)
In-Reply-To: <20190801230744.GA19115@linux.ibm.com>
Currently, rcu_segcblist_restempty() 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() calls, along with the WRITE_ONCE() calls when updating
the callback list.
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
---
kernel/rcu/rcu_segcblist.c | 30 +++++++++++++++---------------
kernel/rcu/rcu_segcblist.h | 2 +-
2 files changed, 16 insertions(+), 16 deletions(-)
diff --git a/kernel/rcu/rcu_segcblist.c b/kernel/rcu/rcu_segcblist.c
index 700779f4c0cb..0e7fe678b6ac 100644
--- a/kernel/rcu/rcu_segcblist.c
+++ b/kernel/rcu/rcu_segcblist.c
@@ -147,8 +147,8 @@ void rcu_segcblist_enqueue(struct rcu_segcblist *rsclp,
rsclp->len_lazy++;
smp_mb(); /* Ensure counts are updated before callback is enqueued. */
rhp->next = NULL;
- *rsclp->tails[RCU_NEXT_TAIL] = rhp;
- rsclp->tails[RCU_NEXT_TAIL] = &rhp->next;
+ WRITE_ONCE(*rsclp->tails[RCU_NEXT_TAIL], rhp);
+ WRITE_ONCE(rsclp->tails[RCU_NEXT_TAIL], &rhp->next);
}
/*
@@ -176,9 +176,9 @@ bool rcu_segcblist_entrain(struct rcu_segcblist *rsclp,
for (i = RCU_NEXT_TAIL; i > RCU_DONE_TAIL; i--)
if (rsclp->tails[i] != rsclp->tails[i - 1])
break;
- *rsclp->tails[i] = rhp;
+ WRITE_ONCE(*rsclp->tails[i], rhp);
for (; i <= RCU_NEXT_TAIL; i++)
- rsclp->tails[i] = &rhp->next;
+ WRITE_ONCE(rsclp->tails[i], &rhp->next);
return true;
}
@@ -214,11 +214,11 @@ void rcu_segcblist_extract_done_cbs(struct rcu_segcblist *rsclp,
return; /* Nothing to do. */
*rclp->tail = rsclp->head;
rsclp->head = *rsclp->tails[RCU_DONE_TAIL];
- *rsclp->tails[RCU_DONE_TAIL] = NULL;
+ 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--)
if (rsclp->tails[i] == rsclp->tails[RCU_DONE_TAIL])
- rsclp->tails[i] = &rsclp->head;
+ WRITE_ONCE(rsclp->tails[i], &rsclp->head);
}
/*
@@ -237,9 +237,9 @@ void rcu_segcblist_extract_pend_cbs(struct rcu_segcblist *rsclp,
return; /* Nothing to do. */
*rclp->tail = *rsclp->tails[RCU_DONE_TAIL];
rclp->tail = rsclp->tails[RCU_NEXT_TAIL];
- *rsclp->tails[RCU_DONE_TAIL] = NULL;
+ WRITE_ONCE(*rsclp->tails[RCU_DONE_TAIL], NULL);
for (i = RCU_DONE_TAIL + 1; i < RCU_CBLIST_NSEGS; i++)
- rsclp->tails[i] = rsclp->tails[RCU_DONE_TAIL];
+ WRITE_ONCE(rsclp->tails[i], rsclp->tails[RCU_DONE_TAIL]);
}
/*
@@ -271,7 +271,7 @@ void rcu_segcblist_insert_done_cbs(struct rcu_segcblist *rsclp,
rsclp->head = rclp->head;
for (i = RCU_DONE_TAIL; i < RCU_CBLIST_NSEGS; i++)
if (&rsclp->head == rsclp->tails[i])
- rsclp->tails[i] = rclp->tail;
+ WRITE_ONCE(rsclp->tails[i], rclp->tail);
else
break;
rclp->head = NULL;
@@ -287,8 +287,8 @@ void rcu_segcblist_insert_pend_cbs(struct rcu_segcblist *rsclp,
{
if (!rclp->head)
return; /* Nothing to do. */
- *rsclp->tails[RCU_NEXT_TAIL] = rclp->head;
- rsclp->tails[RCU_NEXT_TAIL] = rclp->tail;
+ WRITE_ONCE(*rsclp->tails[RCU_NEXT_TAIL], rclp->head);
+ WRITE_ONCE(rsclp->tails[RCU_NEXT_TAIL], rclp->tail);
rclp->head = NULL;
rclp->tail = &rclp->head;
}
@@ -312,7 +312,7 @@ void rcu_segcblist_advance(struct rcu_segcblist *rsclp, unsigned long seq)
for (i = RCU_WAIT_TAIL; i < RCU_NEXT_TAIL; i++) {
if (ULONG_CMP_LT(seq, rsclp->gp_seq[i]))
break;
- rsclp->tails[RCU_DONE_TAIL] = rsclp->tails[i];
+ WRITE_ONCE(rsclp->tails[RCU_DONE_TAIL], rsclp->tails[i]);
}
/* If no callbacks moved, nothing more need be done. */
@@ -321,7 +321,7 @@ void rcu_segcblist_advance(struct rcu_segcblist *rsclp, unsigned long seq)
/* Clean up tail pointers that might have been misordered above. */
for (j = RCU_WAIT_TAIL; j < i; j++)
- rsclp->tails[j] = rsclp->tails[RCU_DONE_TAIL];
+ WRITE_ONCE(rsclp->tails[j], rsclp->tails[RCU_DONE_TAIL]);
/*
* Callbacks moved, so clean up the misordered ->tails[] pointers
@@ -332,7 +332,7 @@ void rcu_segcblist_advance(struct rcu_segcblist *rsclp, unsigned long seq)
for (j = RCU_WAIT_TAIL; i < RCU_NEXT_TAIL; i++, j++) {
if (rsclp->tails[j] == rsclp->tails[RCU_NEXT_TAIL])
break; /* No more callbacks. */
- rsclp->tails[j] = rsclp->tails[i];
+ WRITE_ONCE(rsclp->tails[j], rsclp->tails[i]);
rsclp->gp_seq[j] = rsclp->gp_seq[i];
}
}
@@ -397,7 +397,7 @@ bool rcu_segcblist_accelerate(struct rcu_segcblist *rsclp, unsigned long seq)
* structure other than in the RCU_NEXT_TAIL segment.
*/
for (; i < RCU_NEXT_TAIL; i++) {
- rsclp->tails[i] = rsclp->tails[RCU_NEXT_TAIL];
+ WRITE_ONCE(rsclp->tails[i], rsclp->tails[RCU_NEXT_TAIL]);
rsclp->gp_seq[i] = seq;
}
return true;
diff --git a/kernel/rcu/rcu_segcblist.h b/kernel/rcu/rcu_segcblist.h
index 8f3783391075..f74960f0305c 100644
--- a/kernel/rcu/rcu_segcblist.h
+++ b/kernel/rcu/rcu_segcblist.h
@@ -79,7 +79,7 @@ static inline bool rcu_segcblist_is_offloaded(struct rcu_segcblist *rsclp)
*/
static inline bool rcu_segcblist_restempty(struct rcu_segcblist *rsclp, int seg)
{
- return !*rsclp->tails[seg];
+ return !READ_ONCE(*READ_ONCE(rsclp->tails[seg]));
}
void rcu_segcblist_init(struct rcu_segcblist *rsclp);
--
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 ` Paul E. McKenney [this message]
2019-08-01 23:08 ` [PATCH tip/core/rcu 08/18] rcu/nocb: Allow lockless use of rcu_segcblist_empty() Paul E. McKenney
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
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