On 12/10/24 03:39, Alexei Starovoitov wrote:
> From: Alexei Starovoitov <ast@xxxxxxxxxx>
>
> Similar to local_lock_irqsave() introduce local_trylock_irqsave().
> It uses spin_trylock in PREEMPT_RT and always succeeds when !RT.
Hmm but is that correct to always succeed? If we're in an nmi, we might be
preempting an existing local_(try)lock_irqsave() critical section because
disabling irqs doesn't stop NMI's, right?
> Signed-off-by: Alexei Starovoitov <ast@xxxxxxxxxx>
> ---
> include/linux/local_lock.h | 9 +++++++++
> include/linux/local_lock_internal.h | 23 +++++++++++++++++++++++
> 2 files changed, 32 insertions(+)
>
> diff --git a/include/linux/local_lock.h b/include/linux/local_lock.h
> index 091dc0b6bdfb..6880c29b8b98 100644
> --- a/include/linux/local_lock.h
> +++ b/include/linux/local_lock.h
> @@ -30,6 +30,15 @@
> #define local_lock_irqsave(lock, flags) \
> __local_lock_irqsave(lock, flags)
>
> +/**
> + * local_trylock_irqsave - Try to acquire a per CPU local lock, save and disable
> + * interrupts. Always succeeds in !PREEMPT_RT.
> + * @lock: The lock variable
> + * @flags: Storage for interrupt flags
> + */
> +#define local_trylock_irqsave(lock, flags) \
> + __local_trylock_irqsave(lock, flags)
> +
> /**
> * local_unlock - Release a per CPU local lock
> * @lock: The lock variable
> diff --git a/include/linux/local_lock_internal.h b/include/linux/local_lock_internal.h
> index 8dd71fbbb6d2..2c0f8a49c2d0 100644
> --- a/include/linux/local_lock_internal.h
> +++ b/include/linux/local_lock_internal.h
> @@ -31,6 +31,13 @@ static inline void local_lock_acquire(local_lock_t *l)
> l->owner = current;
> }
>
> +static inline void local_trylock_acquire(local_lock_t *l)
> +{
> + lock_map_acquire_try(&l->dep_map);
> + DEBUG_LOCKS_WARN_ON(l->owner);
> + l->owner = current;
> +}
> +
> static inline void local_lock_release(local_lock_t *l)
> {
> DEBUG_LOCKS_WARN_ON(l->owner != current);
> @@ -45,6 +52,7 @@ static inline void local_lock_debug_init(local_lock_t *l)
> #else /* CONFIG_DEBUG_LOCK_ALLOC */
> # define LOCAL_LOCK_DEBUG_INIT(lockname)
> static inline void local_lock_acquire(local_lock_t *l) { }
> +static inline void local_trylock_acquire(local_lock_t *l) { }
> static inline void local_lock_release(local_lock_t *l) { }
> static inline void local_lock_debug_init(local_lock_t *l) { }
> #endif /* !CONFIG_DEBUG_LOCK_ALLOC */
> @@ -91,6 +99,13 @@ do { \
> local_lock_acquire(this_cpu_ptr(lock)); \
> } while (0)
>
> +#define __local_trylock_irqsave(lock, flags) \
> + ({ \
> + local_irq_save(flags); \
> + local_trylock_acquire(this_cpu_ptr(lock)); \
> + 1; \
> + })
> +
> #define __local_unlock(lock) \
> do { \
> local_lock_release(this_cpu_ptr(lock)); \
> @@ -148,6 +163,14 @@ typedef spinlock_t local_lock_t;
> __local_lock(lock); \
> } while (0)
>
> +#define __local_trylock_irqsave(lock, flags) \
> + ({ \
> + typecheck(unsigned long, flags); \
> + flags = 0; \
> + migrate_disable(); \
> + spin_trylock(this_cpu_ptr((__lock))); \
> + })
> +
> #define __local_unlock(__lock) \
> do { \
> spin_unlock(this_cpu_ptr((__lock))); \
