[v8,10/16] refcount: introduce __refcount_{add|inc}_not_zero_limited

Commit Message

Suren Baghdasaryan Jan. 9, 2025, 2:30 a.m. UTC

Introduce functions to increase refcount but with a top limit above which
they will fail to increase (the limit is inclusive). Setting the limit to
INT_MAX indicates no limit.

Signed-off-by: Suren Baghdasaryan <[e-mail]>
---
 include/linux/refcount.h | 20 +++++++++++++++++++-
 1 file changed, 19 insertions(+), 1 deletion(-)

Comments

Vlastimil Babka Jan. 9, 2025, 2:42 p.m. UTC | #1

On 1/9/25 3:30 AM, Suren Baghdasaryan wrote:
> Introduce functions to increase refcount but with a top limit above which
> they will fail to increase (the limit is inclusive). Setting the limit to
> INT_MAX indicates no limit.
> 
> Signed-off-by: Suren Baghdasaryan <[e-mail]>

Acked-by: Vlastimil Babka <[e-mail]>

Patch

diff --git a/include/linux/refcount.h b/include/linux/refcount.h
index 35f039ecb272..4934247848cf 100644
--- a/include/linux/refcount.h
+++ b/include/linux/refcount.h
@@ -137,13 +137,19 @@  static inline unsigned int refcount_read(const refcount_t *r)
 }
 
 static inline __must_check __signed_wrap
-bool __refcount_add_not_zero(int i, refcount_t *r, int *oldp)
+bool __refcount_add_not_zero_limited(int i, refcount_t *r, int *oldp,
+				     int limit)
 {
 	int old = refcount_read(r);
 
 	do {
 		if (!old)
 			break;
+		if (i > limit - old) {
+			if (oldp)
+				*oldp = old;
+			return false;
+		}
 	} while (!atomic_try_cmpxchg_relaxed(&r->refs, &old, old + i));
 
 	if (oldp)
@@ -155,6 +161,12 @@  bool __refcount_add_not_zero(int i, refcount_t *r, int *oldp)
 	return old;
 }
 
+static inline __must_check __signed_wrap
+bool __refcount_add_not_zero(int i, refcount_t *r, int *oldp)
+{
+	return __refcount_add_not_zero_limited(i, r, oldp, INT_MAX);
+}
+
 /**
  * refcount_add_not_zero - add a value to a refcount unless it is 0
  * @i: the value to add to the refcount
@@ -213,6 +225,12 @@  static inline void refcount_add(int i, refcount_t *r)
 	__refcount_add(i, r, NULL);
 }
 
+static inline __must_check bool __refcount_inc_not_zero_limited(refcount_t *r,
+								int *oldp, int limit)
+{
+	return __refcount_add_not_zero_limited(1, r, oldp, limit);
+}
+
 static inline __must_check bool __refcount_inc_not_zero(refcount_t *r, int *oldp)
 {
 	return __refcount_add_not_zero(1, r, oldp);