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lib/percpu_ida.c: use _irqsave() instead of local_irq_save() + spin_lock

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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>
This commit is contained in:
Sebastian Andrzej Siewior 2018-06-07 17:10:48 -07:00 committed by Linus Torvalds
parent b94078e695
commit 804209d8a0
1 changed files with 21 additions and 42 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

63
lib/percpu_ida.c
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@ -112,18 +112,6 @@ static inline void alloc_global_tags(struct percpu_ida *pool,
min(pool->nr_free, pool->percpu_batch_size));
}
static inline unsigned alloc_local_tag(struct percpu_ida_cpu *tags)
{
int tag = -ENOSPC;
spin_lock(&tags->lock);
if (tags->nr_free)
tag = tags->freelist[--tags->nr_free];
spin_unlock(&tags->lock);
return tag;
}
/**
* percpu_ida_alloc - allocate a tag
* @pool: pool to allocate from
@ -147,20 +135,22 @@ int percpu_ida_alloc(struct percpu_ida *pool, int state)
DEFINE_WAIT(wait);
struct percpu_ida_cpu *tags;
unsigned long flags;
int tag;
int tag = -ENOSPC;
local_irq_save(flags);
tags = this_cpu_ptr(pool->tag_cpu);
tags = raw_cpu_ptr(pool->tag_cpu);
spin_lock_irqsave(&tags->lock, flags);
/* Fastpath */
tag = alloc_local_tag(tags);
if (likely(tag >= 0)) {
local_irq_restore(flags);
if (likely(tags->nr_free >= 0)) {
tag = tags->freelist[--tags->nr_free];
spin_unlock_irqrestore(&tags->lock, flags);
return tag;
}
spin_unlock_irqrestore(&tags->lock, flags);
while (1) {
spin_lock(&pool->lock);
spin_lock_irqsave(&pool->lock, flags);
tags = this_cpu_ptr(pool->tag_cpu);
/*
* prepare_to_wait() must come before steal_tags(), in case
@ -184,8 +174,7 @@ int percpu_ida_alloc(struct percpu_ida *pool, int state)
&pool->cpus_have_tags);
}
spin_unlock(&pool->lock);
local_irq_restore(flags);
spin_unlock_irqrestore(&pool->lock, flags);
if (tag >= 0 || state == TASK_RUNNING)
break;
@ -196,9 +185,6 @@ int percpu_ida_alloc(struct percpu_ida *pool, int state)
}
schedule();
local_irq_save(flags);
tags = this_cpu_ptr(pool->tag_cpu);
}
if (state != TASK_RUNNING)
finish_wait(&pool->wait, &wait);
@ -222,28 +208,24 @@ void percpu_ida_free(struct percpu_ida *pool, unsigned tag)
BUG_ON(tag >= pool->nr_tags);
local_irq_save(flags);
tags = this_cpu_ptr(pool->tag_cpu);
tags = raw_cpu_ptr(pool->tag_cpu);
spin_lock(&tags->lock);
spin_lock_irqsave(&tags->lock, flags);
tags->freelist[tags->nr_free++] = tag;
nr_free = tags->nr_free;
spin_unlock(&tags->lock);
if (nr_free == 1) {
cpumask_set_cpu(smp_processor_id(),
&pool->cpus_have_tags);
wake_up(&pool->wait);
}
spin_unlock_irqrestore(&tags->lock, flags);
if (nr_free == pool->percpu_max_size) {
spin_lock(&pool->lock);
spin_lock_irqsave(&pool->lock, flags);
spin_lock(&tags->lock);
/*
* Global lock held and irqs disabled, don't need percpu
* lock
*/
if (tags->nr_free == pool->percpu_max_size) {
move_tags(pool->freelist, &pool->nr_free,
tags->freelist, &tags->nr_free,
@ -251,10 +233,9 @@ void percpu_ida_free(struct percpu_ida *pool, unsigned tag)
wake_up(&pool->wait);
}
spin_unlock(&pool->lock);
spin_unlock(&tags->lock);
spin_unlock_irqrestore(&pool->lock, flags);
}
local_irq_restore(flags);
}
EXPORT_SYMBOL_GPL(percpu_ida_free);
@ -346,29 +327,27 @@ int percpu_ida_for_each_free(struct percpu_ida *pool, percpu_ida_cb fn,
struct percpu_ida_cpu *remote;
unsigned cpu, i, err = 0;
local_irq_save(flags);
for_each_possible_cpu(cpu) {
remote = per_cpu_ptr(pool->tag_cpu, cpu);
spin_lock(&remote->lock);
spin_lock_irqsave(&remote->lock, flags);
for (i = 0; i < remote->nr_free; i++) {
err = fn(remote->freelist[i], data);
if (err)
break;
}
spin_unlock(&remote->lock);
spin_unlock_irqrestore(&remote->lock, flags);
if (err)
goto out;
}
spin_lock(&pool->lock);
spin_lock_irqsave(&pool->lock, flags);
for (i = 0; i < pool->nr_free; i++) {
err = fn(pool->freelist[i], data);
if (err)
break;
}
spin_unlock(&pool->lock);
spin_unlock_irqrestore(&pool->lock, flags);
out:
local_irq_restore(flags);
return err;
}
EXPORT_SYMBOL_GPL(percpu_ida_for_each_free);