lib/percpu_ida.c: use _irqsave() instead of local_irq_save() + spin_lock
percpu_ida() decouples disabling interrupts from the locking operations. This breaks some assumptions if the locking operations are replaced like they are under -RT. The same locking can be achieved by avoiding local_irq_save() and using spin_lock_irqsave() instead. percpu_ida_alloc() gains one more preemption point because after unlocking the fastpath and before the pool lock is acquired, the interrupts are briefly enabled. Link: http://lkml.kernel.org/r/20180504153218.7301-1-bigeasy@linutronix.de Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Reviewed-by: Andrew Morton <akpm@linux-foundation.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Nicholas Bellinger <nab@linux-iscsi.org> Cc: Shaohua Li <shli@fb.com> Cc: Kent Overstreet <kent.overstreet@gmail.com> Cc: Matthew Wilcox <willy@infradead.org> Cc: Jens Axboe <axboe@kernel.dk> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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@ -112,18 +112,6 @@ static inline void alloc_global_tags(struct percpu_ida *pool,
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min(pool->nr_free, pool->percpu_batch_size));
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}
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static inline unsigned alloc_local_tag(struct percpu_ida_cpu *tags)
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{
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int tag = -ENOSPC;
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spin_lock(&tags->lock);
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if (tags->nr_free)
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tag = tags->freelist[--tags->nr_free];
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spin_unlock(&tags->lock);
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return tag;
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}
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/**
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* percpu_ida_alloc - allocate a tag
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* @pool: pool to allocate from
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@ -147,20 +135,22 @@ int percpu_ida_alloc(struct percpu_ida *pool, int state)
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DEFINE_WAIT(wait);
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struct percpu_ida_cpu *tags;
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unsigned long flags;
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int tag;
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int tag = -ENOSPC;
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local_irq_save(flags);
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tags = this_cpu_ptr(pool->tag_cpu);
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tags = raw_cpu_ptr(pool->tag_cpu);
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spin_lock_irqsave(&tags->lock, flags);
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/* Fastpath */
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tag = alloc_local_tag(tags);
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if (likely(tag >= 0)) {
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local_irq_restore(flags);
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if (likely(tags->nr_free >= 0)) {
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tag = tags->freelist[--tags->nr_free];
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spin_unlock_irqrestore(&tags->lock, flags);
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return tag;
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}
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spin_unlock_irqrestore(&tags->lock, flags);
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while (1) {
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spin_lock(&pool->lock);
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spin_lock_irqsave(&pool->lock, flags);
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tags = this_cpu_ptr(pool->tag_cpu);
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/*
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* prepare_to_wait() must come before steal_tags(), in case
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@ -184,8 +174,7 @@ int percpu_ida_alloc(struct percpu_ida *pool, int state)
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&pool->cpus_have_tags);
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}
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spin_unlock(&pool->lock);
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local_irq_restore(flags);
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spin_unlock_irqrestore(&pool->lock, flags);
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if (tag >= 0 || state == TASK_RUNNING)
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break;
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@ -196,9 +185,6 @@ int percpu_ida_alloc(struct percpu_ida *pool, int state)
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}
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schedule();
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local_irq_save(flags);
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tags = this_cpu_ptr(pool->tag_cpu);
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}
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if (state != TASK_RUNNING)
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finish_wait(&pool->wait, &wait);
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@ -222,28 +208,24 @@ void percpu_ida_free(struct percpu_ida *pool, unsigned tag)
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BUG_ON(tag >= pool->nr_tags);
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local_irq_save(flags);
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tags = this_cpu_ptr(pool->tag_cpu);
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tags = raw_cpu_ptr(pool->tag_cpu);
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spin_lock(&tags->lock);
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spin_lock_irqsave(&tags->lock, flags);
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tags->freelist[tags->nr_free++] = tag;
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nr_free = tags->nr_free;
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spin_unlock(&tags->lock);
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if (nr_free == 1) {
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cpumask_set_cpu(smp_processor_id(),
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&pool->cpus_have_tags);
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wake_up(&pool->wait);
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}
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spin_unlock_irqrestore(&tags->lock, flags);
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if (nr_free == pool->percpu_max_size) {
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spin_lock(&pool->lock);
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spin_lock_irqsave(&pool->lock, flags);
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spin_lock(&tags->lock);
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/*
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* Global lock held and irqs disabled, don't need percpu
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* lock
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*/
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if (tags->nr_free == pool->percpu_max_size) {
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move_tags(pool->freelist, &pool->nr_free,
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tags->freelist, &tags->nr_free,
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@ -251,10 +233,9 @@ void percpu_ida_free(struct percpu_ida *pool, unsigned tag)
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wake_up(&pool->wait);
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}
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spin_unlock(&pool->lock);
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spin_unlock(&tags->lock);
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spin_unlock_irqrestore(&pool->lock, flags);
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}
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local_irq_restore(flags);
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}
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EXPORT_SYMBOL_GPL(percpu_ida_free);
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@ -346,29 +327,27 @@ int percpu_ida_for_each_free(struct percpu_ida *pool, percpu_ida_cb fn,
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struct percpu_ida_cpu *remote;
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unsigned cpu, i, err = 0;
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local_irq_save(flags);
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for_each_possible_cpu(cpu) {
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remote = per_cpu_ptr(pool->tag_cpu, cpu);
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spin_lock(&remote->lock);
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spin_lock_irqsave(&remote->lock, flags);
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for (i = 0; i < remote->nr_free; i++) {
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err = fn(remote->freelist[i], data);
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if (err)
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break;
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}
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spin_unlock(&remote->lock);
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spin_unlock_irqrestore(&remote->lock, flags);
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if (err)
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goto out;
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}
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spin_lock(&pool->lock);
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spin_lock_irqsave(&pool->lock, flags);
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for (i = 0; i < pool->nr_free; i++) {
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err = fn(pool->freelist[i], data);
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if (err)
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break;
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}
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spin_unlock(&pool->lock);
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spin_unlock_irqrestore(&pool->lock, flags);
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out:
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local_irq_restore(flags);
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return err;
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}
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EXPORT_SYMBOL_GPL(percpu_ida_for_each_free);
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