The patch titled
Subject: lib/percpu_ida.c: use _irqsave() instead of local_irq_save() + spin_lock
has been added to the -mm tree. Its filename is
percpu_ida-use-_irqsave-instead-of-local_irq_save-spin_lock.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/percpu_ida-use-_irqsave-instead-of-local_irq_save-spin_lock.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/percpu_ida-use-_irqsave-instead-of-local_irq_save-spin_lock.patch
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------------------------------------------------------
From: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
Subject: 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@xxxxxxxxxxxxx
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
Reviewed-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Nicholas Bellinger <nab@xxxxxxxxxxxxxxx>
Cc: Shaohua Li <shli@xxxxxx>
Cc: Kent Overstreet <kent.overstreet@xxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Cc: Jens Axboe <axboe@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
lib/percpu_ida.c | 63 +++++++++++++++------------------------------
1 file changed, 21 insertions(+), 42 deletions(-)
diff -puN lib/percpu_ida.c~percpu_ida-use-_irqsave-instead-of-local_irq_save-spin_lock lib/percpu_ida.c
--- a/lib/percpu_ida.c~percpu_ida-use-_irqsave-instead-of-local_irq_save-spin_lock
+++ a/lib/percpu_ida.c
@@ -112,18 +112,6 @@ static inline void alloc_global_tags(str
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 *
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->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 *
}
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 *
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 *
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 perc
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);
_
Patches currently in -mm which might be from bigeasy@xxxxxxxxxxxxx are
percpu_ida-use-_irqsave-instead-of-local_irq_save-spin_lock.patch
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