linux-kernel - [PATCH v7 6/7] rqspinlock: Use smp_cond_load_acquire

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Message-Id: <20251017061606.455701-7-ankur.a.arora@oracle.com>
Date: Thu, 16 Oct 2025 23:16:05 -0700
From: Ankur Arora <ankur.a.arora@...cle.com>
To: linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, bpf@...r.kernel.org
Cc: arnd@...db.de, catalin.marinas@....com, will@...nel.org,
        peterz@...radead.org, akpm@...ux-foundation.org, mark.rutland@....com,
        harisokn@...zon.com, cl@...two.org, ast@...nel.org, rafael@...nel.org,
        daniel.lezcano@...aro.org, memxor@...il.com, zhenglifeng1@...wei.com,
        xueshuai@...ux.alibaba.com, joao.m.martins@...cle.com,
        boris.ostrovsky@...cle.com, konrad.wilk@...cle.com
Subject: [PATCH v7 6/7] rqspinlock: Use smp_cond_load_acquire_timeout()

Switch out the conditional load interfaces used by rqspinlock
to atomic_cond_read_acquire_timeout(), and
smp_cond_read_acquire_timeout().

Both these handle the timeout and amortize as needed, so use
check_timeout() directly.

Also, when using spin-wait implementations, redefine SMP_TIMEOUT_POLL_COUNT
to be 16k to be similar to the spin-count used in RES_CHECK_TIMEOUT().

Cc: Kumar Kartikeya Dwivedi <memxor@...il.com>
Cc: Alexei Starovoitov <ast@...nel.org>
Signed-off-by: Ankur Arora <ankur.a.arora@...cle.com>
---
 kernel/bpf/rqspinlock.c | 31 ++++++++++++++-----------------
 1 file changed, 14 insertions(+), 17 deletions(-)

diff --git a/kernel/bpf/rqspinlock.c b/kernel/bpf/rqspinlock.c
index a00561b1d3e5..f35f078a158d 100644
--- a/kernel/bpf/rqspinlock.c
+++ b/kernel/bpf/rqspinlock.c
@@ -241,20 +241,14 @@ static noinline int check_timeout(rqspinlock_t *lock, u32 mask,
 }
 
 /*
- * Do not amortize with spins when res_smp_cond_load_acquire is defined,
- * as the macro does internal amortization for us.
+ * Amortize timeout check for busy-wait loops.
  */
-#ifndef res_smp_cond_load_acquire
 #define RES_CHECK_TIMEOUT(ts, ret, mask)                              \
 	({                                                            \
 		if (!(ts).spin++)                                     \
 			(ret) = check_timeout((lock), (mask), &(ts)); \
 		(ret);                                                \
 	})
-#else
-#define RES_CHECK_TIMEOUT(ts, ret, mask)			      \
-	({ (ret) = check_timeout((lock), (mask), &(ts)); })
-#endif
 
 /*
  * Initialize the 'spin' member.
@@ -268,6 +262,16 @@ static noinline int check_timeout(rqspinlock_t *lock, u32 mask,
  */
 #define RES_RESET_TIMEOUT(ts, _duration) ({ (ts).timeout_end = 0; (ts).duration = _duration; })
 
+/*
+ * Limit how often check_timeout() is invoked while spin-waiting in
+ * smp_cond_load_acquire_timeout() or atomic_cond_read_acquire_timeout().
+ * (ARM64, typically uses a waited implementation so we exclude that.)
+ */
+#ifndef CONFIG_ARM64
+#undef SMP_TIMEOUT_POLL_COUNT
+#define SMP_TIMEOUT_POLL_COUNT	(16*1024)
+#endif
+
 /*
  * Provide a test-and-set fallback for cases when queued spin lock support is
  * absent from the architecture.
@@ -313,12 +316,6 @@ EXPORT_SYMBOL_GPL(resilient_tas_spin_lock);
  */
 static DEFINE_PER_CPU_ALIGNED(struct qnode, rqnodes[_Q_MAX_NODES]);
 
-#ifndef res_smp_cond_load_acquire
-#define res_smp_cond_load_acquire(v, c) smp_cond_load_acquire(v, c)
-#endif
-
-#define res_atomic_cond_read_acquire(v, c) res_smp_cond_load_acquire(&(v)->counter, (c))
-
 /**
  * resilient_queued_spin_lock_slowpath - acquire the queued spinlock
  * @lock: Pointer to queued spinlock structure
@@ -418,7 +415,8 @@ 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));
+		smp_cond_load_acquire_timeout(&lock->locked, !VAL,
+					      (ret = check_timeout(lock, _Q_LOCKED_MASK, &ts)));
 	}
 
 	if (ret) {
@@ -572,9 +570,8 @@ int __lockfunc resilient_queued_spin_lock_slowpath(rqspinlock_t *lock, u32 val)
 	 * us.
 	 */
 	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));
-
+	val = atomic_cond_read_acquire_timeout(&lock->val, !(VAL & _Q_LOCKED_PENDING_MASK),
+					       (ret = check_timeout(lock, _Q_LOCKED_PENDING_MASK, &ts)));
 waitq_timeout:
 	if (ret) {
 		/*
-- 
2.43.5