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SubjectRe: [RFC PATCH v1 02/25] printk-rb: add prb locking functions
On (02/12/19 15:29), John Ogness wrote:
> +static bool __prb_trylock(struct prb_cpulock *cpu_lock,
> + unsigned int *cpu_store)
> +{
> + unsigned long *flags;
> + unsigned int cpu;
> +
> + cpu = get_cpu();
> +
> + *cpu_store = atomic_read(&cpu_lock->owner);
> + /* memory barrier to ensure the current lock owner is visible */
> + smp_rmb();
> + if (*cpu_store == -1) {
> + flags = per_cpu_ptr(cpu_lock->irqflags, cpu);
> + local_irq_save(*flags);
> + if (atomic_try_cmpxchg_acquire(&cpu_lock->owner,
> + cpu_store, cpu)) {
> + return true;
> + }
> + local_irq_restore(*flags);
> + } else if (*cpu_store == cpu) {
> + return true;
> + }
> +
> + put_cpu();
> + return false;
> +}
> +
> +/*
> + * prb_lock: Perform a processor-reentrant spin lock.
> + * @cpu_lock: A pointer to the lock object.
> + * @cpu_store: A "flags" pointer to store lock status information.
> + *
> + * If no processor has the lock, the calling processor takes the lock and
> + * becomes the owner. If the calling processor is already the owner of the
> + * lock, this function succeeds immediately. If lock is locked by another
> + * processor, this function spins until the calling processor becomes the
> + * owner.
> + *
> + * It is safe to call this function from any context and state.
> + */
> +void prb_lock(struct prb_cpulock *cpu_lock, unsigned int *cpu_store)
> +{
> + for (;;) {
> + if (__prb_trylock(cpu_lock, cpu_store))
> + break;
> + cpu_relax();
> + }
> +}

Any chance to make it more fair? A ticket based lock, perhaps?

-ss

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