[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <174670044066.406.12184664540495493769.tip-bot2@tip-bot2>
Date: Thu, 08 May 2025 10:34:00 -0000
From: "tip-bot2 for Sebastian Andrzej Siewior" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
"Peter Zijlstra (Intel)" <peterz@...radead.org>, x86@...nel.org,
linux-kernel@...r.kernel.org
Subject: [tip: locking/futex] rcuref: Provide rcuref_is_dead()
The following commit has been merged into the locking/futex branch of tip:
Commit-ID: 3efa66ce6ee1b55ab687b316e48e1e9ddc1f780a
Gitweb: https://git.kernel.org/tip/3efa66ce6ee1b55ab687b316e48e1e9ddc1f780a
Author: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
AuthorDate: Wed, 16 Apr 2025 18:29:01 +02:00
Committer: Peter Zijlstra <peterz@...radead.org>
CommitterDate: Sat, 03 May 2025 12:02:04 +02:00
rcuref: Provide rcuref_is_dead()
rcuref_read() returns the number of references that are currently held.
If 0 is returned then it is not safe to assume that the object ca be
scheduled for deconstruction because it is marked DEAD. This happens if
the return value of rcuref_put() is ignored and assumptions are made.
If 0 is returned then the counter transitioned from 0 to RCUREF_NOREF.
If rcuref_put() did not return to the caller then the counter did not
yet transition from RCUREF_NOREF to RCUREF_DEAD. This means that there
is still a chance that the counter will transition from RCUREF_NOREF to
0 meaning it is still valid and must not be deconstructed. In this brief
window rcuref_read() will return 0.
Provide rcuref_is_dead() to determine if the counter is marked as
RCUREF_DEAD.
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Link: https://lore.kernel.org/r/20250416162921.513656-2-bigeasy@linutronix.de
---
include/linux/rcuref.h | 22 +++++++++++++++++++++-
1 file changed, 21 insertions(+), 1 deletion(-)
diff --git a/include/linux/rcuref.h b/include/linux/rcuref.h
index 6322d8c..2fb2af6 100644
--- a/include/linux/rcuref.h
+++ b/include/linux/rcuref.h
@@ -30,7 +30,11 @@ static inline void rcuref_init(rcuref_t *ref, unsigned int cnt)
* rcuref_read - Read the number of held reference counts of a rcuref
* @ref: Pointer to the reference count
*
- * Return: The number of held references (0 ... N)
+ * Return: The number of held references (0 ... N). The value 0 does not
+ * indicate that it is safe to schedule the object, protected by this reference
+ * counter, for deconstruction.
+ * If you want to know if the reference counter has been marked DEAD (as
+ * signaled by rcuref_put()) please use rcuread_is_dead().
*/
static inline unsigned int rcuref_read(rcuref_t *ref)
{
@@ -40,6 +44,22 @@ static inline unsigned int rcuref_read(rcuref_t *ref)
return c >= RCUREF_RELEASED ? 0 : c + 1;
}
+/**
+ * rcuref_is_dead - Check if the rcuref has been already marked dead
+ * @ref: Pointer to the reference count
+ *
+ * Return: True if the object has been marked DEAD. This signals that a previous
+ * invocation of rcuref_put() returned true on this reference counter meaning
+ * the protected object can safely be scheduled for deconstruction.
+ * Otherwise, returns false.
+ */
+static inline bool rcuref_is_dead(rcuref_t *ref)
+{
+ unsigned int c = atomic_read(&ref->refcnt);
+
+ return (c >= RCUREF_RELEASED) && (c < RCUREF_NOREF);
+}
+
extern __must_check bool rcuref_get_slowpath(rcuref_t *ref);
/**
Powered by blists - more mailing lists