On 2025-01-23 19:56:52 [-0800], Alexei Starovoitov wrote:
> Usage:
>
> local_lock_t lock; // sizeof(lock) == 0 in !RT
> local_lock_irqsave(&lock, ...); // irqsave as before
> if (local_trylock_irqsave(&lock, ...)) // compilation error
>
> local_trylock_t lock; // sizeof(lock) == 4 in !RT
> local_lock_irqsave(&lock, ...); // irqsave and active = 1
> if (local_trylock_irqsave(&lock, ...)) // if (!active) irqsave
so I've been looking at this for a while and I don't like the part where
the type is hidden away. It is then casted back. So I tried something
with _Generics but then the existing guard implementation complained.
Then I asked myself why do we want to hide much of the implementation
and not make it obvious. So I made a few macros to hide most of the
implementation for !RT. Later I figured if the variable is saved locally
then I save one this_cpu_ptr invocation. So I wrote it out and the
snippet below is what I have.
is this anywhere near possible to accept?
diff --git a/include/linux/local_lock.h b/include/linux/local_lock.h
index 091dc0b6bdfb9..05c254a5d7d3e 100644
--- a/include/linux/local_lock.h
+++ b/include/linux/local_lock.h
@@ -51,6 +51,65 @@
#define local_unlock_irqrestore(lock, flags) \
__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
+ */
+#define localtry_lock_irqsave(lock, flags) \
+ __localtry_lock_irqsave(lock, flags)
+
+/**
+ * localtry_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
+ *
+ * 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 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_GUARD(local_lock, local_lock_t __percpu*,
local_lock(_T),
local_unlock(_T))
diff --git a/include/linux/local_lock_internal.h b/include/linux/local_lock_internal.h
index 8dd71fbbb6d2b..789b0d878e6c5 100644
--- a/include/linux/local_lock_internal.h
+++ b/include/linux/local_lock_internal.h
@@ -15,6 +15,11 @@ typedef struct {
#endif
} local_lock_t;
+typedef struct {
+ local_lock_t llock;
+ unsigned int acquired;
+} localtry_lock_t;
+
#ifdef CONFIG_DEBUG_LOCK_ALLOC
# define LOCAL_LOCK_DEBUG_INIT(lockname) \
.dep_map = { \
@@ -50,6 +55,7 @@ static inline void local_lock_debug_init(local_lock_t *l) { }
#endif /* !CONFIG_DEBUG_LOCK_ALLOC */
#define INIT_LOCAL_LOCK(lockname) { LOCAL_LOCK_DEBUG_INIT(lockname) }
+#define INIT_LOCALTRY_LOCK(lockname) { .llock = { LOCAL_LOCK_DEBUG_INIT(lockname.llock) }}
#define __local_lock_init(lock) \
do { \
@@ -118,6 +124,86 @@ do { \
#define __local_unlock_nested_bh(lock) \
local_lock_release(this_cpu_ptr(lock))
+/* localtry_lock_t variants */
+
+#define __localtry_lock_init(lock) \
+do { \
+ __local_lock_init(&(lock)->llock); \
+ WRITE_ONCE(&(lock)->acquired, 0); \
+} while (0)
+
+#define __localtry_lock(lock) \
+ do { \
+ localtry_lock_t *lt; \
+ preempt_disable(); \
+ lt = this_cpu_ptr(lock); \
+ local_lock_acquire(<->llock); \
+ WRITE_ONCE(lt->acquired, 1); \
+ } while (0)
+
+#define __localtry_lock_irq(lock) \
+ do { \
+ localtry_lock_t *lt; \
+ local_irq_disable(); \
+ lt = this_cpu_ptr(lock); \
+ local_lock_acquire(<->llock); \
+ WRITE_ONCE(lt->acquired, 1); \
+ } while (0)
+
+#define __localtry_lock_irqsave(lock, flags) \
+ do { \
+ localtry_lock_t *lt; \
+ local_irq_save(flags); \
+ lt = this_cpu_ptr(lock); \
+ local_lock_acquire(<->llock); \
+ WRITE_ONCE(lt->acquired, 1); \
+ } while (0)
+
+#define __localtry_trylock_irqsave(lock, flags) \
+ ({ \
+ localtry_lock_t *lt; \
+ bool _ret; \
+ \
+ local_irq_save(flags); \
+ lt = this_cpu_ptr(lock); \
+ if (!READ_ONCE(lt->acquired)) { \
+ local_lock_acquire(<->llock); \
+ WRITE_ONCE(lt->acquired, 1); \
+ _ret = true; \
+ } else { \
+ _ret = false; \
+ local_irq_restore(flags); \
+ } \
+ _ret; \
+ })
+
+#define __localtry_unlock(lock) \
+ do { \
+ localtry_lock_t *lt; \
+ lt = this_cpu_ptr(lock); \
+ WRITE_ONCE(lt->acquired, 0); \
+ local_lock_release(<->llock); \
+ preempt_enable(); \
+ } while (0)
+
+#define __localtry_unlock_irq(lock) \
+ do { \
+ localtry_lock_t *lt; \
+ lt = this_cpu_ptr(lock); \
+ WRITE_ONCE(lt->acquired, 0); \
+ local_lock_release(<->llock); \
+ local_irq_enable(); \
+ } while (0)
+
+#define __localtry_unlock_irqrestore(lock, flags) \
+ do { \
+ localtry_lock_t *lt; \
+ lt = this_cpu_ptr(lock); \
+ WRITE_ONCE(lt->acquired, 0); \
+ local_lock_release(<->llock); \
+ local_irq_restore(flags); \
+ } while (0)
+
#else /* !CONFIG_PREEMPT_RT */
/*
@@ -125,8 +211,10 @@ do { \
* critical section while staying preemptible.
*/
typedef spinlock_t local_lock_t;
+typedef spinlock_t localtry_lock_t;
#define INIT_LOCAL_LOCK(lockname) __LOCAL_SPIN_LOCK_UNLOCKED((lockname))
+#define INIT_LOCALTRY_LOCK(lockname) INIT_LOCAL_LOCK(lockname)
#define __local_lock_init(l) \
do { \
@@ -169,4 +257,31 @@ do { \
spin_unlock(this_cpu_ptr((lock))); \
} while (0)
+/* localtry_lock_t variants */
+
+#define __localtry_lock_init(lock) __local_lock_init(lock)
+#define __localtry_lock(lock) __local_lock(lock)
+#define __localtry_lock_irq(lock) __local_lock(lock)
+#define __localtry_lock_irqsave(lock, flags) __local_lock_irqsave(lock, flags)
+#define __localtry_unlock(lock) __local_unlock(lock)
+#define __localtry_unlock_irq(lock) __local_unlock(lock)
+#define __localtry_unlock_irqrestore(lock, flags) __local_unlock_irqrestore(lock, flags)
+
+#define __localtry_trylock_irqsave(lock, flags) \
+ ({ \
+ int __locked; \
+ \
+ typecheck(unsigned long, flags); \
+ flags = 0; \
+ if (in_nmi() | in_hardirq()) { \
+ __locked = 0; \
+ } else { \
+ migrate_disable(); \
+ __locked = spin_trylock(this_cpu_ptr((lock))); \
+ if (!__locked) \
+ migrate_enable(); \
+ } \
+ __locked; \
+ })
+
#endif /* CONFIG_PREEMPT_RT */
