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McKenney" , Tejun Heo , Barret Rhoden , Josh Don , Dohyun Kim , linux-arm-kernel@lists.infradead.org, kernel-team@meta.com Subject: [PATCH bpf-next v2 12/26] rqspinlock: Add a test-and-set fallback Date: Thu, 6 Feb 2025 02:54:20 -0800 Message-ID: <20250206105435.2159977-13-memxor@gmail.com> X-Mailer: git-send-email 2.43.5 In-Reply-To: <20250206105435.2159977-1-memxor@gmail.com> References: <20250206105435.2159977-1-memxor@gmail.com> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Developer-Signature: v=1; a=openpgp-sha256; l=3427; h=from:subject; bh=nWMxFCMQuXMGccLr9BZ8Vd2VRz48kOmVrJhLP51E7zU=; b=owEBbQKS/ZANAwAIAUzgyIZIvxHKAcsmYgBnpJRlMFpWa3g5n8jTl6bpUsPGHtx8MXyfjnnCKJt9 AHs008SJAjMEAAEIAB0WIQRLvip+Buz51YI8YRFM4MiGSL8RygUCZ6SUZQAKCRBM4MiGSL8RyvWnD/ 9ElDHw+LJcUwAOu/LB12XiFVDPKFpTcnqBAIIgWpttUZIU9wtEERsQL0IYyZVGNxKf6NjzmCa5aWjB 6dG2OM5EHYXz75cwkHfgazZPzdvgoVeDK/X6Rt2/k5eFlhkvDpaZ1RJQQbPSvRy3B4iNrYvUxPRntH 0siGNJGxXXk2/BF8QAsO0/9VyB0myTjnkvBLTYazkhPxYeGYJPOVUfjk9cl5Z2kz+zKGi7S7EVov5k EoVNvIcbjJp6aOpxZ0Cl81l9juNQk5dH73X0Y6yLqqcmxRePAdscK6ygQ0v6j5b5bZg1vt9NqzHfbx bcepMH3rFrZmAqXnSuel7pnTFM4tuaOV9SyNfh2zbTXiyWyQFXxPuGFx1+OLztjitTNulOf0KE+BUh HpLSN8XCqNmM10ErdfqRD80ZDXesuP0vqDokTCpTWKQXbVlnLiWGEwIOnyoE0LWBwqn/XvqhOIFrv4 DYsmQzW+k7QJRAtKWsWYpWOHweuglwIcQeVSluJEnfGNkaIUyHbEU8X0V7jEnkdX5De3i1bERuidMP wM5fvNrUBt5JbXAuZjfP1QaTVtQYh+Rc0k6cDl6I0PUPAi5aAglDK3T8+HJtDTOjLvWN3st8/uhyl5 rLuvZDv3ZySigXnWcS+rrjCZ06WAgFBD5LZbLsv4etjiyzSaJO4h2bT6JiIA== X-Developer-Key: i=memxor@gmail.com; a=openpgp; fpr=4BBE2A7E06ECF9D5823C61114CE0C88648BF11CA X-Patchwork-Delegate: bpf@iogearbox.net Include a test-and-set fallback when queued spinlock support is not available. Introduce a rqspinlock type to act as a fallback when qspinlock support is absent. Include ifdef guards to ensure the slow path in this file is only compiled when CONFIG_QUEUED_SPINLOCKS=y. Subsequent patches will add further logic to ensure fallback to the test-and-set implementation when queued spinlock support is unavailable on an architecture. Signed-off-by: Kumar Kartikeya Dwivedi --- include/asm-generic/rqspinlock.h | 17 +++++++++++++++ kernel/locking/rqspinlock.c | 37 ++++++++++++++++++++++++++++++++ 2 files changed, 54 insertions(+) diff --git a/include/asm-generic/rqspinlock.h b/include/asm-generic/rqspinlock.h index c1dbd25287a1..92e53b2aafb9 100644 --- a/include/asm-generic/rqspinlock.h +++ b/include/asm-generic/rqspinlock.h @@ -12,11 +12,28 @@ #include #include #include +#ifdef CONFIG_QUEUED_SPINLOCKS +#include +#endif + +struct rqspinlock { + union { + atomic_t val; + u32 locked; + }; +}; struct qspinlock; +#ifdef CONFIG_QUEUED_SPINLOCKS typedef struct qspinlock rqspinlock_t; +#else +typedef struct rqspinlock rqspinlock_t; +#endif +extern int resilient_tas_spin_lock(rqspinlock_t *lock, u64 timeout); +#ifdef CONFIG_QUEUED_SPINLOCKS extern int resilient_queued_spin_lock_slowpath(rqspinlock_t *lock, u32 val, u64 timeout); +#endif /* * Default timeout for waiting loops is 0.5 seconds diff --git a/kernel/locking/rqspinlock.c b/kernel/locking/rqspinlock.c index 42e8a56534b6..ea034e80f855 100644 --- a/kernel/locking/rqspinlock.c +++ b/kernel/locking/rqspinlock.c @@ -21,7 +21,9 @@ #include #include #include +#ifdef CONFIG_QUEUED_SPINLOCKS #include +#endif #include #include #include @@ -29,8 +31,10 @@ /* * Include queued spinlock definitions and statistics code */ +#ifdef CONFIG_QUEUED_SPINLOCKS #include "qspinlock.h" #include "rqspinlock.h" +#endif #include "qspinlock_stat.h" /* @@ -252,6 +256,37 @@ static noinline int check_timeout(rqspinlock_t *lock, u32 mask, */ #define RES_RESET_TIMEOUT(ts) ({ (ts).timeout_end = 0; }) +/* + * Provide a test-and-set fallback for cases when queued spin lock support is + * absent from the architecture. + */ +int __lockfunc resilient_tas_spin_lock(rqspinlock_t *lock, u64 timeout) +{ + struct rqspinlock_timeout ts; + int val, ret = 0; + + RES_INIT_TIMEOUT(ts, timeout); + grab_held_lock_entry(lock); +retry: + val = atomic_read(&lock->val); + + if (val || !atomic_try_cmpxchg(&lock->val, &val, 1)) { + if (RES_CHECK_TIMEOUT(ts, ret, ~0u)) { + lockevent_inc(rqspinlock_lock_timeout); + goto out; + } + cpu_relax(); + goto retry; + } + + return 0; +out: + release_held_lock_entry(); + return ret; +} + +#ifdef CONFIG_QUEUED_SPINLOCKS + /* * Per-CPU queue node structures; we can never have more than 4 nested * contexts: task, softirq, hardirq, nmi. @@ -581,3 +616,5 @@ int __lockfunc resilient_queued_spin_lock_slowpath(rqspinlock_t *lock, u32 val, return ret; } EXPORT_SYMBOL(resilient_queued_spin_lock_slowpath); + +#endif /* CONFIG_QUEUED_SPINLOCKS */