From: "Paul E. McKenney" <paulmck@kernel.org>
To: rcu@vger.kernel.org, linux-kernel@vger.kernel.org
Cc: kernel-team@meta.com,
Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
Boqun Feng <boqun@kernel.org>,
Steven Rostedt <rostedt@goodmis.org>,
lkmm@lists.linux.dev, Zqiang <qiang.zhang@linux.dev>,
Wang Lian <lianux.mm@gmail.com>,
Kunwu Chan <kunwu.chan@gmail.com>,
Bradley Morgan <brads@mainlining.org>,
"Paul E . McKenney" <paulmck@kernel.org>
Subject: [PATCH 19/28] hazptr: Permit detaching hazard pointers from contexts
Date: Fri, 18 Sep 2026 17:00:47 -0700 [thread overview]
Message-ID: <20260919000056.3132131-19-paulmck@kernel.org> (raw)
In-Reply-To: <e9669b34-12c2-4cf2-a887-315f581f0789@paulmck-laptop>
From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Provide a new hazptr_detach() function that detaches a given hazard
pointer from its acquisition context. This context might be a task or
an interrupt handler.
[ paulmck: s/hazptr_detach_from_task/hazptr_detach/ per Mathieu. ]
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Cc: Boqun Feng <boqun@kernel.org>
Cc: <rcu@vger.kernel.org>
Cc: <lkmm@lists.linux.dev>
---
include/linux/hazptr.h | 55 ++++++++++++++++++++++++++++--------------
1 file changed, 37 insertions(+), 18 deletions(-)
diff --git a/include/linux/hazptr.h b/include/linux/hazptr.h
index b121f7779cda..8197a51b9f7a 100644
--- a/include/linux/hazptr.h
+++ b/include/linux/hazptr.h
@@ -98,6 +98,41 @@ bool hazptr_slot_is_backup(struct hazptr_ctx *ctx, struct hazptr_slot *slot)
return slot == &ctx->backup_slot.slot;
}
+/* Internal helper. */
+static inline
+void hazptr_promote_to_backup_slot(struct hazptr_ctx *ctx, struct hazptr_slot *slot)
+{
+ struct hazptr_slot *backup_slot;
+
+ backup_slot = hazptr_chain_backup_slot(ctx);
+ /*
+ * Move hazard pointer from the per-CPU slot to the
+ * backup slot. This requires hazard pointer
+ * synchronize to iterate on per-CPU slots with
+ * load-acquire before iterating on the overflow list.
+ */
+ WRITE_ONCE(backup_slot->addr, slot->addr);
+ /*
+ * store-release orders store to backup slot addr before
+ * store to per-CPU slot addr.
+ */
+ smp_store_release(&slot->addr, NULL);
+ /* Use the backup slot for context. */
+ ctx->slot = backup_slot;
+}
+
+static inline
+void hazptr_detach(struct hazptr_ctx *ctx)
+{
+ struct hazptr_slot *slot;
+
+ guard(preempt)();
+ slot = ctx->slot;
+ if (unlikely(hazptr_slot_is_backup(ctx, slot)))
+ return;
+ hazptr_promote_to_backup_slot(ctx, slot);
+}
+
static inline
void hazptr_note_context_switch(void)
{
@@ -106,27 +141,11 @@ void hazptr_note_context_switch(void)
for (idx = 0; idx < NR_HAZPTR_PERCPU_SLOTS; idx++) {
struct hazptr_slot_item *item = &percpu_slots->items[idx];
- struct hazptr_slot *slot = &item->slot, *backup_slot;
- struct hazptr_ctx *ctx;
+ struct hazptr_slot *slot = &item->slot;
if (!slot->addr)
continue;
- ctx = item->ctx.ctx;
- backup_slot = hazptr_chain_backup_slot(ctx);
- /*
- * Move hazard pointer from the per-CPU slot to the
- * backup slot. This requires hazard pointer
- * synchronize to iterate on per-CPU slots with
- * load-acquire before iterating on the overflow list.
- */
- WRITE_ONCE(backup_slot->addr, slot->addr);
- /*
- * store-release orders store to backup slot addr before
- * store to per-CPU slot addr.
- */
- smp_store_release(&slot->addr, NULL);
- /* Use the backup slot for context. */
- ctx->slot = backup_slot;
+ hazptr_promote_to_backup_slot(item->ctx.ctx, slot);
}
}
--
2.40.1
next prev parent reply other threads:[~2026-09-19 0:01 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-09-18 23:59 [PATCH RFC v3 0/28] Simple hazard-pointer implementation and torture tests Paul E. McKenney
2026-09-19 0:00 ` [PATCH 01/28] hazptr: Implement Hazard Pointers Paul E. McKenney
2026-09-19 0:00 ` [PATCH 02/28] hazptr: Add refscale test Paul E. McKenney
2026-09-19 0:00 ` [PATCH 03/28] torture: Add a hazptrtorture.c torture test Paul E. McKenney
2026-09-19 0:00 ` [PATCH 04/28] hazptrtorture: Add testing of on-stack hazptr_ctx structures Paul E. McKenney
2026-09-19 0:00 ` [PATCH 05/28] hazptrtorture: Add microsecond-scale sleep in readers Paul E. McKenney
2026-09-19 0:00 ` [PATCH 06/28] hazptrtorture: Enable system-independent CPU overcommit Paul E. McKenney
2026-09-19 0:00 ` [PATCH 07/28] torture: Add a stutter_will_wait() function Paul E. McKenney
2026-09-19 0:00 ` [PATCH 08/28] hazptrtorture: Use mnemonic local variables for context information Paul E. McKenney
2026-09-19 0:00 ` [PATCH 09/28] hazptrtorture: Split hazptr_torture_reader_tail() from hazptr_torture_reader() Paul E. McKenney
2026-09-19 0:00 ` [PATCH 10/28] hazptrtorture: Add kthread to release deferred hazard pointers Paul E. McKenney
2026-09-19 0:00 ` [PATCH 11/28] hazptrtorture: Defer release of " Paul E. McKenney
2026-09-19 0:00 ` [PATCH 12/28] hazptrtorture: Add irq_acquire to acquire hazptr from irq Paul E. McKenney
2026-09-19 0:00 ` [PATCH 13/28] hazptrtorture: Use task_state_to_char() for task-state reporting Paul E. McKenney
2026-09-19 0:00 ` [PATCH 14/28] hazptrtorture: Pass hazptr_pending to hazptr_torture_reader_tail() Paul E. McKenney
2026-09-19 0:00 ` [PATCH 15/28] hazptrtorture: Add the ability to disable the writer kthread Paul E. McKenney
2026-09-19 0:00 ` [PATCH 16/28] hazptrtorture: Add irq_release to release hazptr from irq Paul E. McKenney
2026-09-19 0:00 ` [PATCH 17/28] hazptrtorture: Accumulate operation statistics Paul E. McKenney
2026-09-19 0:00 ` [PATCH 18/28] doc: Add hazptrtorture module parameters Paul E. McKenney
2026-09-19 0:00 ` Paul E. McKenney [this message]
2026-09-19 0:00 ` [PATCH 20/28] hazptrtorture: Detach deferred and IPIed hazard pointers Paul E. McKenney
2026-09-19 0:00 ` [PATCH 21/28] hazptr: Introduce CONFIG_HAZPTR_DEBUG misuse detection Paul E. McKenney
2026-09-19 0:00 ` [PATCH 22/28] hazptrtorture: Fix hazptr ownership issue Paul E. McKenney
2026-09-19 0:00 ` [PATCH 23/28] hazptrtorture: Enable CONFIG_HAZPTR_DEBUG Paul E. McKenney
2026-09-19 0:00 ` [PATCH 24/28] hazptr: Upgrade kernel-doc headers Paul E. McKenney
2026-09-19 0:00 ` [PATCH 25/28] hazptrtorture: Fix inverted sleep condition in do_pending kthread Paul E. McKenney
2026-09-19 0:00 ` [PATCH 26/28] hazptr: Implement two-phase wildcard scan Paul E. McKenney
2026-09-19 0:00 ` [PATCH 27/28] hazptr: handle NULL address in hazptr_detach Paul E. McKenney
2026-09-19 0:00 ` [PATCH 28/28] torture.sh: Add hazptr torturing Paul E. McKenney
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