diff options
| author | Sebastian Andrzej Siewior <bigeasy@linutronix.de> | 2025-04-16 18:29:01 +0200 |
|---|---|---|
| committer | Peter Zijlstra <peterz@infradead.org> | 2025-05-03 12:02:04 +0200 |
| commit | 3efa66ce6ee1b55ab687b316e48e1e9ddc1f780a (patch) | |
| tree | 427f2fe8041ef5427cdbf73d202f5fb8c1c1a43f | |
| parent | b4432656b36e5cc1d50a1f2dc15357543add530e (diff) | |
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@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20250416162921.513656-2-bigeasy@linutronix.de
| -rw-r--r-- | include/linux/rcuref.h | 22 |
1 files changed, 21 insertions, 1 deletions
diff --git a/include/linux/rcuref.h b/include/linux/rcuref.h index 6322d8c1c6b4..2fb2af6d9824 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); /** |