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authorTejun Heo <tj@kernel.org>2014-09-24 13:31:50 -0400
committerTejun Heo <tj@kernel.org>2014-09-24 13:31:50 -0400
commit2aad2a86f6685c10360ec8a5a55eb9ab7059cb72 (patch)
tree85da25f36ba0c8158becdc8ba940201652cf30ce
parentf47ad45784611297b699f3dffb6c7222b76afe64 (diff)
downloadlinux-2aad2a86f6685c10360ec8a5a55eb9ab7059cb72.tar.bz2
percpu_ref: add PERCPU_REF_INIT_* flags
With the recent addition of percpu_ref_reinit(), percpu_ref now can be used as a persistent switch which can be turned on and off repeatedly where turning off maps to killing the ref and waiting for it to drain; however, there currently isn't a way to initialize a percpu_ref in its off (killed and drained) state, which can be inconvenient for certain persistent switch use cases. Similarly, percpu_ref_switch_to_atomic/percpu() allow dynamic selection of operation mode; however, currently a newly initialized percpu_ref is always in percpu mode making it impossible to avoid the latency overhead of switching to atomic mode. This patch adds @flags to percpu_ref_init() and implements the following flags. * PERCPU_REF_INIT_ATOMIC : start ref in atomic mode * PERCPU_REF_INIT_DEAD : start ref killed and drained These flags should be able to serve the above two use cases. v2: target_core_tpg.c conversion was missing. Fixed. Signed-off-by: Tejun Heo <tj@kernel.org> Reviewed-by: Kent Overstreet <kmo@daterainc.com> Cc: Jens Axboe <axboe@kernel.dk> Cc: Christoph Hellwig <hch@infradead.org> Cc: Johannes Weiner <hannes@cmpxchg.org>
-rw-r--r--block/blk-mq.c2
-rw-r--r--drivers/target/target_core_tpg.c2
-rw-r--r--fs/aio.c4
-rw-r--r--include/linux/percpu-refcount.h18
-rw-r--r--kernel/cgroup.c7
-rw-r--r--lib/percpu-refcount.c23
6 files changed, 43 insertions, 13 deletions
diff --git a/block/blk-mq.c b/block/blk-mq.c
index 44a78ae3f899..d85fe01c44ef 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -1796,7 +1796,7 @@ struct request_queue *blk_mq_init_queue(struct blk_mq_tag_set *set)
goto err_hctxs;
if (percpu_ref_init(&q->mq_usage_counter, blk_mq_usage_counter_release,
- GFP_KERNEL))
+ 0, GFP_KERNEL))
goto err_map;
setup_timer(&q->timeout, blk_mq_rq_timer, (unsigned long) q);
diff --git a/drivers/target/target_core_tpg.c b/drivers/target/target_core_tpg.c
index 4ab6da338585..be783f717f19 100644
--- a/drivers/target/target_core_tpg.c
+++ b/drivers/target/target_core_tpg.c
@@ -819,7 +819,7 @@ int core_tpg_add_lun(
{
int ret;
- ret = percpu_ref_init(&lun->lun_ref, core_tpg_lun_ref_release,
+ ret = percpu_ref_init(&lun->lun_ref, core_tpg_lun_ref_release, 0,
GFP_KERNEL);
if (ret < 0)
return ret;
diff --git a/fs/aio.c b/fs/aio.c
index 8d217ed04e6e..84a751005f5b 100644
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -661,10 +661,10 @@ static struct kioctx *ioctx_alloc(unsigned nr_events)
INIT_LIST_HEAD(&ctx->active_reqs);
- if (percpu_ref_init(&ctx->users, free_ioctx_users, GFP_KERNEL))
+ if (percpu_ref_init(&ctx->users, free_ioctx_users, 0, GFP_KERNEL))
goto err;
- if (percpu_ref_init(&ctx->reqs, free_ioctx_reqs, GFP_KERNEL))
+ if (percpu_ref_init(&ctx->reqs, free_ioctx_reqs, 0, GFP_KERNEL))
goto err;
ctx->cpu = alloc_percpu(struct kioctx_cpu);
diff --git a/include/linux/percpu-refcount.h b/include/linux/percpu-refcount.h
index cd7e20f0fe47..b0293f268cd2 100644
--- a/include/linux/percpu-refcount.h
+++ b/include/linux/percpu-refcount.h
@@ -63,6 +63,21 @@ enum {
__PERCPU_REF_FLAG_BITS = 2,
};
+/* @flags for percpu_ref_init() */
+enum {
+ /*
+ * Start w/ ref == 1 in atomic mode. Can be switched to percpu
+ * operation using percpu_ref_switch_to_percpu().
+ */
+ PERCPU_REF_INIT_ATOMIC = 1 << 0,
+
+ /*
+ * Start dead w/ ref == 0 in atomic mode. Must be revived with
+ * percpu_ref_reinit() before used. Implies INIT_ATOMIC.
+ */
+ PERCPU_REF_INIT_DEAD = 1 << 1,
+};
+
struct percpu_ref {
atomic_long_t count;
/*
@@ -76,7 +91,8 @@ struct percpu_ref {
};
int __must_check percpu_ref_init(struct percpu_ref *ref,
- percpu_ref_func_t *release, gfp_t gfp);
+ percpu_ref_func_t *release, unsigned int flags,
+ gfp_t gfp);
void percpu_ref_exit(struct percpu_ref *ref);
void percpu_ref_switch_to_atomic(struct percpu_ref *ref,
percpu_ref_func_t *confirm_switch);
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index a99d504294de..753df01a9831 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -1634,7 +1634,8 @@ static int cgroup_setup_root(struct cgroup_root *root, unsigned int ss_mask)
goto out;
root_cgrp->id = ret;
- ret = percpu_ref_init(&root_cgrp->self.refcnt, css_release, GFP_KERNEL);
+ ret = percpu_ref_init(&root_cgrp->self.refcnt, css_release, 0,
+ GFP_KERNEL);
if (ret)
goto out;
@@ -4510,7 +4511,7 @@ static int create_css(struct cgroup *cgrp, struct cgroup_subsys *ss,
init_and_link_css(css, ss, cgrp);
- err = percpu_ref_init(&css->refcnt, css_release, GFP_KERNEL);
+ err = percpu_ref_init(&css->refcnt, css_release, 0, GFP_KERNEL);
if (err)
goto err_free_css;
@@ -4583,7 +4584,7 @@ static int cgroup_mkdir(struct kernfs_node *parent_kn, const char *name,
goto out_unlock;
}
- ret = percpu_ref_init(&cgrp->self.refcnt, css_release, GFP_KERNEL);
+ ret = percpu_ref_init(&cgrp->self.refcnt, css_release, 0, GFP_KERNEL);
if (ret)
goto out_free_cgrp;
diff --git a/lib/percpu-refcount.c b/lib/percpu-refcount.c
index 5a6d43baccc5..ed280fb1e5b5 100644
--- a/lib/percpu-refcount.c
+++ b/lib/percpu-refcount.c
@@ -45,27 +45,40 @@ static unsigned long __percpu *percpu_count_ptr(struct percpu_ref *ref)
* percpu_ref_init - initialize a percpu refcount
* @ref: percpu_ref to initialize
* @release: function which will be called when refcount hits 0
+ * @flags: PERCPU_REF_INIT_* flags
* @gfp: allocation mask to use
*
- * Initializes the refcount in single atomic counter mode with a refcount of 1;
- * analagous to atomic_long_set(ref, 1).
+ * Initializes @ref. If @flags is zero, @ref starts in percpu mode with a
+ * refcount of 1; analagous to atomic_long_set(ref, 1). See the
+ * definitions of PERCPU_REF_INIT_* flags for flag behaviors.
*
* Note that @release must not sleep - it may potentially be called from RCU
* callback context by percpu_ref_kill().
*/
int percpu_ref_init(struct percpu_ref *ref, percpu_ref_func_t *release,
- gfp_t gfp)
+ unsigned int flags, gfp_t gfp)
{
size_t align = max_t(size_t, 1 << __PERCPU_REF_FLAG_BITS,
__alignof__(unsigned long));
-
- atomic_long_set(&ref->count, 1 + PERCPU_COUNT_BIAS);
+ unsigned long start_count = 0;
ref->percpu_count_ptr = (unsigned long)
__alloc_percpu_gfp(sizeof(unsigned long), align, gfp);
if (!ref->percpu_count_ptr)
return -ENOMEM;
+ if (flags & (PERCPU_REF_INIT_ATOMIC | PERCPU_REF_INIT_DEAD))
+ ref->percpu_count_ptr |= __PERCPU_REF_ATOMIC;
+ else
+ start_count += PERCPU_COUNT_BIAS;
+
+ if (flags & PERCPU_REF_INIT_DEAD)
+ ref->percpu_count_ptr |= __PERCPU_REF_DEAD;
+ else
+ start_count++;
+
+ atomic_long_set(&ref->count, start_count);
+
ref->release = release;
return 0;
}