linux-kernel - [PATCH v4 5/5] rqspinlock: use smp_cond_load_acquire

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Message-Id: <20250829080735.3598416-6-ankur.a.arora@oracle.com>
Date: Fri, 29 Aug 2025 01:07:35 -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, 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 v4 5/5] rqspinlock: use smp_cond_load_acquire_timewait()

Use smp_cond_load_acquire_timewait() to define
res_atomic_cond_read_acquire() and res_smp_cond_load_acquire_timewait().

The timeout check for both is done via RES_CHECK_TIMEOUT(). Define
res_smp_cond_load_acquire_waiting() to allow it to amortize the
check for spin-wait implementations.

Cc: Kumar Kartikeya Dwivedi <memxor@...il.com>
Cc: Alexei Starovoitov <ast@...nel.org>
Signed-off-by: Ankur Arora <ankur.a.arora@...cle.com>
---
 arch/arm64/include/asm/rqspinlock.h |  3 +++
 include/asm-generic/rqspinlock.h    |  4 ++++
 kernel/bpf/rqspinlock.c             | 25 +++++++++----------------
 3 files changed, 16 insertions(+), 16 deletions(-)

diff --git a/arch/arm64/include/asm/rqspinlock.h b/arch/arm64/include/asm/rqspinlock.h
index a385603436e9..ce8feadeb9a9 100644
--- a/arch/arm64/include/asm/rqspinlock.h
+++ b/arch/arm64/include/asm/rqspinlock.h
@@ -3,6 +3,9 @@
 #define _ASM_RQSPINLOCK_H
 
 #include <asm/barrier.h>
+
+#define res_smp_cond_load_acquire_waiting() arch_timer_evtstrm_available()
+
 #include <asm-generic/rqspinlock.h>
 
 #endif /* _ASM_RQSPINLOCK_H */
diff --git a/include/asm-generic/rqspinlock.h b/include/asm-generic/rqspinlock.h
index 6d4244d643df..4b49c0ddf89a 100644
--- a/include/asm-generic/rqspinlock.h
+++ b/include/asm-generic/rqspinlock.h
@@ -247,4 +247,8 @@ static __always_inline void res_spin_unlock(rqspinlock_t *lock)
 
 #define raw_res_spin_unlock_irqrestore(lock, flags) ({ raw_res_spin_unlock(lock); local_irq_restore(flags); })
 
+#ifndef res_smp_cond_load_acquire_waiting
+#define res_smp_cond_load_acquire_waiting()	0
+#endif
+
 #endif /* __ASM_GENERIC_RQSPINLOCK_H */
diff --git a/kernel/bpf/rqspinlock.c b/kernel/bpf/rqspinlock.c
index 5ab354d55d82..8de1395422e8 100644
--- a/kernel/bpf/rqspinlock.c
+++ b/kernel/bpf/rqspinlock.c
@@ -82,6 +82,7 @@ struct rqspinlock_timeout {
 	u64 duration;
 	u64 cur;
 	u16 spin;
+	u8  wait;
 };
 
 #define RES_TIMEOUT_VAL	2
@@ -241,26 +242,20 @@ 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.
+ * Only amortize with spins when we don't have a waiting implementation.
  */
-#ifndef res_smp_cond_load_acquire
 #define RES_CHECK_TIMEOUT(ts, ret, mask)                              \
 	({                                                            \
-		if (!(ts).spin++)                                     \
+		if ((ts).wait || !(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.
  * Set spin member to 0 to trigger AA/ABBA checks immediately.
  */
-#define RES_INIT_TIMEOUT(ts) ({ (ts).spin = 0; })
+#define RES_INIT_TIMEOUT(ts) ({ (ts).spin = 0; (ts).wait = res_smp_cond_load_acquire_waiting(); })
 
 /*
  * We only need to reset 'timeout_end', 'spin' will just wrap around as necessary.
@@ -313,11 +308,8 @@ 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))
+#define res_atomic_cond_read_acquire(v, c, t)		smp_cond_load_acquire_timewait(&(v)->counter, (c), (t))
+#define res_smp_cond_load_acquire_timewait(v, c, t)	smp_cond_load_acquire_timewait(v, (c), (t))
 
 /**
  * resilient_queued_spin_lock_slowpath - acquire the queued spinlock
@@ -418,7 +410,8 @@ 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));
+		res_smp_cond_load_acquire_timewait(&lock->locked, !VAL,
+						   RES_CHECK_TIMEOUT(ts, ret, _Q_LOCKED_MASK));
 	}
 
 	if (ret) {
@@ -572,7 +565,7 @@ 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) ||
+	val = res_atomic_cond_read_acquire(&lock->val, !(VAL & _Q_LOCKED_PENDING_MASK),
 					   RES_CHECK_TIMEOUT(ts, ret, _Q_LOCKED_PENDING_MASK));
 
 waitq_timeout:
-- 
2.31.1