[PATCH v13 09/15] bpf/rqspinlock: switch check_timeout() to a clock interface

From: Ankur Arora <hidden>
Date: 2026-07-02 01:35:10
Also in: bpf, linux-arch, linux-pm, lkml
Subsystem: bpf [general] (safe dynamic programs and tools), the rest · Maintainers: Alexei Starovoitov, Daniel Borkmann, Andrii Nakryiko, Eduard Zingerman, Kumar Kartikeya Dwivedi, Linus Torvalds

check_timeout() gets the current time value and depending on how
much time has passed, checks for deadlock or times out, returning 0
or -errno on deadlock or timeout.

Switch this out to a clock style interface, where it functions as a
clock in the "lock-domain", returning the current time until a
deadlock or timeout occurs. Once a deadlock or timeout has occurred,
it stops functioning as a clock and returns error.

Also adjust the RES_CHECK_TIMEOUT macro to discard the clock value
when updating the explicit return status.

Cc: bpf@vger.kernel.org
Cc: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Cc: Alexei Starovoitov <ast@kernel.org>
Acked-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Signed-off-by: Ankur Arora <redacted>
---
 kernel/bpf/rqspinlock.c | 45 +++++++++++++++++++++++++++--------------
 1 file changed, 30 insertions(+), 15 deletions(-)

diff --git a/kernel/bpf/rqspinlock.c b/kernel/bpf/rqspinlock.c
index e4e338cdb437..0ec17ebb67c1 100644
--- a/kernel/bpf/rqspinlock.c
+++ b/kernel/bpf/rqspinlock.c

@@ -196,8 +196,12 @@ static noinline int check_deadlock_ABBA(rqspinlock_t *lock, u32 mask)
 	return 0;
 }
 
-static noinline int check_timeout(rqspinlock_t *lock, u32 mask,
-				  struct rqspinlock_timeout *ts)
+/*
+ * Returns current monotonic time in ns on success or, negative errno
+ * value on failure due to timeout expiration or detection of deadlock.
+ */
+static noinline s64 clock_deadlock(rqspinlock_t *lock, u32 mask,
+				   struct rqspinlock_timeout *ts)
 {
 	u64 prev = ts->cur;
 	u64 time;

@@ -207,7 +211,7 @@ static noinline int check_timeout(rqspinlock_t *lock, u32 mask,
 			return -EDEADLK;
 		ts->cur = ktime_get_mono_fast_ns();
 		ts->timeout_end = ts->cur + ts->duration;
-		return 0;
+		return (s64)ts->cur;
 	}
 
 	time = ktime_get_mono_fast_ns();

@@ -219,11 +223,15 @@ static noinline int check_timeout(rqspinlock_t *lock, u32 mask,
 	 * checks.
 	 */
 	if (prev + NSEC_PER_MSEC < time) {
+		int ret;
 		ts->cur = time;
-		return check_deadlock_ABBA(lock, mask);
+		ret = check_deadlock_ABBA(lock, mask);
+		if (ret)
+			return ret;
+
 	}
 
-	return 0;
+	return (s64)time;
 }
 
 /*

@@ -231,15 +239,22 @@ static noinline int check_timeout(rqspinlock_t *lock, u32 mask,
  * as the macro does internal amortization for us.
  */
 #ifndef res_smp_cond_load_acquire
-#define RES_CHECK_TIMEOUT(ts, ret, mask)                              \
-	({                                                            \
-		if (!(ts).spin++)                                     \
-			(ret) = check_timeout((lock), (mask), &(ts)); \
-		(ret);                                                \
+#define RES_CHECK_TIMEOUT(ts, ret, mask)					\
+	({									\
+		s64 __timeval_err = 0;						\
+		if (!(ts).spin++)						\
+			__timeval_err = clock_deadlock((lock), (mask), &(ts));	\
+		(ret) = __timeval_err < 0 ? __timeval_err : 0;			\
+		__timeval_err;							\
 	})
 #else
-#define RES_CHECK_TIMEOUT(ts, ret, mask)			      \
-	({ (ret) = check_timeout((lock), (mask), &(ts)); })
+#define RES_CHECK_TIMEOUT(ts, ret, mask)					\
+	({									\
+		s64 __timeval_err;						\
+		__timeval_err = clock_deadlock((lock), (mask), &(ts));		\
+		(ret) = __timeval_err < 0 ? __timeval_err : 0;			\
+		__timeval_err;							\
+	})
 #endif
 
 /*

@@ -281,7 +296,7 @@ int __lockfunc resilient_tas_spin_lock(rqspinlock_t *lock)
 	val = atomic_read(&lock->val);
 
 	if (val || !atomic_try_cmpxchg(&lock->val, &val, 1)) {
-		if (RES_CHECK_TIMEOUT(ts, ret, ~0u))
+		if (RES_CHECK_TIMEOUT(ts, ret, ~0u) < 0)
 			goto out;
 		cpu_relax();
 		goto retry;

@@ -406,7 +421,7 @@ int __lockfunc resilient_queued_spin_lock_slowpath(rqspinlock_t *lock, u32 val)
 	 */
 	if (val & _Q_LOCKED_MASK) {
 		RES_RESET_TIMEOUT(ts, RES_DEF_TIMEOUT);
-		res_smp_cond_load_acquire(&lock->locked, !VAL || RES_CHECK_TIMEOUT(ts, ret, _Q_LOCKED_MASK));
+		res_smp_cond_load_acquire(&lock->locked, !VAL || RES_CHECK_TIMEOUT(ts, ret, _Q_LOCKED_MASK) < 0);
 	}
 
 	if (ret) {

@@ -568,7 +583,7 @@ int __lockfunc resilient_queued_spin_lock_slowpath(rqspinlock_t *lock, u32 val)
 	 */
 	RES_RESET_TIMEOUT(ts, RES_DEF_TIMEOUT * 2);
 	val = res_atomic_cond_read_acquire(&lock->val, !(VAL & _Q_LOCKED_PENDING_MASK) ||
-					   RES_CHECK_TIMEOUT(ts, ret, _Q_LOCKED_PENDING_MASK));
+					   RES_CHECK_TIMEOUT(ts, ret, _Q_LOCKED_PENDING_MASK) < 0);
 
 	/* Disable queue destruction when we detect deadlocks. */
 	if (ret == -EDEADLK) {

-- 
2.43.7

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