From 51339d99c0131bc0d16d378e9b05bc498d2967e2 Mon Sep 17 00:00:00 2001 From: Alexei Starovoitov Date: Wed, 2 Apr 2025 19:55:14 -0700 Subject: locking/local_lock, mm: replace localtry_ helpers with local_trylock_t type Partially revert commit 0aaddfb06882 ("locking/local_lock: Introduce localtry_lock_t"). Remove localtry_*() helpers, since localtry_lock() name might be misinterpreted as "try lock". Introduce local_trylock[_irqsave]() helpers that only work with newly introduced local_trylock_t type. Note that attempt to use local_trylock[_irqsave]() with local_lock_t will cause compilation failure. Usage and behavior in !PREEMPT_RT: local_lock_t lock; // sizeof(lock) == 0 local_lock(&lock); // preempt disable local_lock_irqsave(&lock, ...); // irq save if (local_trylock_irqsave(&lock, ...)) // compilation error local_trylock_t lock; // sizeof(lock) == 4 local_lock(&lock); // preempt disable, acquired = 1 local_lock_irqsave(&lock, ...); // irq save, acquired = 1 if (local_trylock(&lock)) // if (!acquired) preempt disable, acquired = 1 if (local_trylock_irqsave(&lock, ...)) // if (!acquired) irq save, acquired = 1 The existing local_lock_*() macros can be used either with local_lock_t or local_trylock_t. With local_trylock_t they set acquired = 1 while local_unlock_*() clears it. In !PREEMPT_RT local_lock_irqsave(local_lock_t *) disables interrupts to protect critical section, but it doesn't prevent NMI, so the fully reentrant code cannot use local_lock_irqsave(local_lock_t *) for exclusive access. The local_lock_irqsave(local_trylock_t *) helper disables interrupts and sets acquired=1, so local_trylock_irqsave(local_trylock_t *) from NMI attempting to acquire the same lock will return false. In PREEMPT_RT local_lock_irqsave() maps to preemptible spin_lock(). Map local_trylock_irqsave() to preemptible spin_trylock(). When in hard IRQ or NMI return false right away, since spin_trylock() is not safe due to explicit locking in the underneath rt_spin_trylock() implementation. Removing this explicit locking and attempting only "trylock" is undesired due to PI implications. The local_trylock() without _irqsave can be used to avoid the cost of disabling/enabling interrupts by only disabling preemption, so local_trylock() in an interrupt attempting to acquire the same lock will return false. Note there is no need to use local_inc for acquired variable, since it's a percpu variable with strict nesting scopes. Note that guard(local_lock)(&lock) works only for "local_lock_t lock". The patch also makes sure that local_lock_release(l) is called before WRITE_ONCE(l->acquired, 0). Though IRQs are disabled at this point the local_trylock() from NMI will succeed and local_lock_acquire(l) will warn. Link: https://lkml.kernel.org/r/20250403025514.41186-1-alexei.starovoitov@gmail.com Fixes: 0aaddfb06882 ("locking/local_lock: Introduce localtry_lock_t") Signed-off-by: Alexei Starovoitov Acked-by: Vlastimil Babka Acked-by: Sebastian Andrzej Siewior Reviewed-by: Shakeel Butt Cc: Daniel Borkman Cc: Linus Torvalds Cc: Martin KaFai Lau Cc: Michal Hocko Cc: Peter Zijlstra Cc: Steven Rostedt Cc: Vlastimil Babka Signed-off-by: Andrew Morton --- include/linux/local_lock.h | 58 +++++++--------------------------------------- 1 file changed, 8 insertions(+), 50 deletions(-) (limited to 'include/linux/local_lock.h') diff --git a/include/linux/local_lock.h b/include/linux/local_lock.h index 1a0bc35839e3..16a2ee4f8310 100644 --- a/include/linux/local_lock.h +++ b/include/linux/local_lock.h @@ -52,44 +52,23 @@ __local_unlock_irqrestore(lock, flags) /** - * localtry_lock_init - Runtime initialize a lock instance - */ -#define localtry_lock_init(lock) __localtry_lock_init(lock) - -/** - * localtry_lock - Acquire a per CPU local lock - * @lock: The lock variable - */ -#define localtry_lock(lock) __localtry_lock(lock) - -/** - * localtry_lock_irq - Acquire a per CPU local lock and disable interrupts - * @lock: The lock variable - */ -#define localtry_lock_irq(lock) __localtry_lock_irq(lock) - -/** - * localtry_lock_irqsave - Acquire a per CPU local lock, save and disable - * interrupts - * @lock: The lock variable - * @flags: Storage for interrupt flags + * local_lock_init - Runtime initialize a lock instance */ -#define localtry_lock_irqsave(lock, flags) \ - __localtry_lock_irqsave(lock, flags) +#define local_trylock_init(lock) __local_trylock_init(lock) /** - * localtry_trylock - Try to acquire a per CPU local lock. + * local_trylock - Try to acquire a per CPU local lock * @lock: The lock variable * * The function can be used in any context such as NMI or HARDIRQ. Due to * locking constrains it will _always_ fail to acquire the lock in NMI or * HARDIRQ context on PREEMPT_RT. */ -#define localtry_trylock(lock) __localtry_trylock(lock) +#define local_trylock(lock) __local_trylock(lock) /** - * localtry_trylock_irqsave - Try to acquire a per CPU local lock, save and disable - * interrupts if acquired + * local_trylock_irqsave - Try to acquire a per CPU local lock, save and disable + * interrupts if acquired * @lock: The lock variable * @flags: Storage for interrupt flags * @@ -97,29 +76,8 @@ * locking constrains it will _always_ fail to acquire the lock in NMI or * HARDIRQ context on PREEMPT_RT. */ -#define localtry_trylock_irqsave(lock, flags) \ - __localtry_trylock_irqsave(lock, flags) - -/** - * local_unlock - Release a per CPU local lock - * @lock: The lock variable - */ -#define localtry_unlock(lock) __localtry_unlock(lock) - -/** - * local_unlock_irq - Release a per CPU local lock and enable interrupts - * @lock: The lock variable - */ -#define localtry_unlock_irq(lock) __localtry_unlock_irq(lock) - -/** - * localtry_unlock_irqrestore - Release a per CPU local lock and restore - * interrupt flags - * @lock: The lock variable - * @flags: Interrupt flags to restore - */ -#define localtry_unlock_irqrestore(lock, flags) \ - __localtry_unlock_irqrestore(lock, flags) +#define local_trylock_irqsave(lock, flags) \ + __local_trylock_irqsave(lock, flags) DEFINE_GUARD(local_lock, local_lock_t __percpu*, local_lock(_T), -- cgit v1.2.3