lkml.org 
[lkml]   [2018]   [Mar]   [6]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[PATCH 7/7] RCU, workqueue: Implement rcu_work
Date
There are cases where RCU callback needs to be bounced to a sleepable
context. This is currently done by the RCU callback queueing a work
item, which can be cumbersome to write and confusing to read.

This patch introduces rcu_work, a workqueue work variant which gets
executed after a RCU grace period, and converts the open coded
bouncing in fs/aio and kernel/cgroup.

v2: Use rcu_barrier() instead of synchronize_rcu() to wait for
completion of previously queued rcu callback as per Paul.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
---
fs/aio.c | 21 +++++-------------
include/linux/cgroup-defs.h | 2 +-
include/linux/workqueue.h | 38 +++++++++++++++++++++++++++++++
kernel/cgroup/cgroup.c | 21 ++++++------------
kernel/workqueue.c | 54 +++++++++++++++++++++++++++++++++++++++++++++
5 files changed, 106 insertions(+), 30 deletions(-)

diff --git a/fs/aio.c b/fs/aio.c
index 6bcd3fb..88d7927 100644
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -115,8 +115,7 @@ struct kioctx {
struct page **ring_pages;
long nr_pages;

- struct rcu_head free_rcu;
- struct work_struct free_work; /* see free_ioctx() */
+ struct rcu_work free_rwork; /* see free_ioctx() */

/*
* signals when all in-flight requests are done
@@ -592,13 +591,12 @@ static int kiocb_cancel(struct aio_kiocb *kiocb)
/*
* free_ioctx() should be RCU delayed to synchronize against the RCU
* protected lookup_ioctx() and also needs process context to call
- * aio_free_ring(), so the double bouncing through kioctx->free_rcu and
- * ->free_work.
+ * aio_free_ring(). Use rcu_work.
*/
static void free_ioctx(struct work_struct *work)
{
- struct kioctx *ctx = container_of(work, struct kioctx, free_work);
-
+ struct kioctx *ctx = container_of(to_rcu_work(work), struct kioctx,
+ free_rwork);
pr_debug("freeing %p\n", ctx);

aio_free_ring(ctx);
@@ -608,14 +606,6 @@ static void free_ioctx(struct work_struct *work)
kmem_cache_free(kioctx_cachep, ctx);
}

-static void free_ioctx_rcufn(struct rcu_head *head)
-{
- struct kioctx *ctx = container_of(head, struct kioctx, free_rcu);
-
- INIT_WORK(&ctx->free_work, free_ioctx);
- schedule_work(&ctx->free_work);
-}
-
static void free_ioctx_reqs(struct percpu_ref *ref)
{
struct kioctx *ctx = container_of(ref, struct kioctx, reqs);
@@ -625,7 +615,8 @@ static void free_ioctx_reqs(struct percpu_ref *ref)
complete(&ctx->rq_wait->comp);

/* Synchronize against RCU protected table->table[] dereferences */
- call_rcu(&ctx->free_rcu, free_ioctx_rcufn);
+ INIT_RCU_WORK(&ctx->free_rwork, free_ioctx);
+ queue_rcu_work(system_wq, &ctx->free_rwork);
}

/*
diff --git a/include/linux/cgroup-defs.h b/include/linux/cgroup-defs.h
index 9f242b8..92d7640 100644
--- a/include/linux/cgroup-defs.h
+++ b/include/linux/cgroup-defs.h
@@ -151,8 +151,8 @@ struct cgroup_subsys_state {
atomic_t online_cnt;

/* percpu_ref killing and RCU release */
- struct rcu_head rcu_head;
struct work_struct destroy_work;
+ struct rcu_work destroy_rwork;

/*
* PI: the parent css. Placed here for cache proximity to following
diff --git a/include/linux/workqueue.h b/include/linux/workqueue.h
index bc0cda1..b39f3a4 100644
--- a/include/linux/workqueue.h
+++ b/include/linux/workqueue.h
@@ -13,6 +13,7 @@
#include <linux/threads.h>
#include <linux/atomic.h>
#include <linux/cpumask.h>
+#include <linux/rcupdate.h>

struct workqueue_struct;

@@ -120,6 +121,15 @@ struct delayed_work {
int cpu;
};

+struct rcu_work {
+ struct work_struct work;
+ struct rcu_head rcu;
+
+ /* target workqueue and CPU ->rcu uses to queue ->work */
+ struct workqueue_struct *wq;
+ int cpu;
+};
+
/**
* struct workqueue_attrs - A struct for workqueue attributes.
*
@@ -151,6 +161,11 @@ static inline struct delayed_work *to_delayed_work(struct work_struct *work)
return container_of(work, struct delayed_work, work);
}

+static inline struct rcu_work *to_rcu_work(struct work_struct *work)
+{
+ return container_of(work, struct rcu_work, work);
+}
+
struct execute_work {
struct work_struct work;
};
@@ -266,6 +281,12 @@ static inline unsigned int work_static(struct work_struct *work) { return 0; }
#define INIT_DEFERRABLE_WORK_ONSTACK(_work, _func) \
__INIT_DELAYED_WORK_ONSTACK(_work, _func, TIMER_DEFERRABLE)

+#define INIT_RCU_WORK(_work, _func) \
+ INIT_WORK(&(_work)->work, (_func))
+
+#define INIT_RCU_WORK_ONSTACK(_work, _func) \
+ INIT_WORK_ONSTACK(&(_work)->work, (_func))
+
/**
* work_pending - Find out whether a work item is currently pending
* @work: The work item in question
@@ -447,6 +468,8 @@ extern bool queue_delayed_work_on(int cpu, struct workqueue_struct *wq,
struct delayed_work *work, unsigned long delay);
extern bool mod_delayed_work_on(int cpu, struct workqueue_struct *wq,
struct delayed_work *dwork, unsigned long delay);
+extern bool queue_rcu_work_on(int cpu, struct workqueue_struct *wq,
+ struct rcu_work *rwork);

extern void flush_workqueue(struct workqueue_struct *wq);
extern void drain_workqueue(struct workqueue_struct *wq);
@@ -463,6 +486,8 @@ extern bool flush_delayed_work(struct delayed_work *dwork);
extern bool cancel_delayed_work(struct delayed_work *dwork);
extern bool cancel_delayed_work_sync(struct delayed_work *dwork);

+extern bool flush_rcu_work(struct rcu_work *rwork);
+
extern void workqueue_set_max_active(struct workqueue_struct *wq,
int max_active);
extern struct work_struct *current_work(void);
@@ -520,6 +545,19 @@ static inline bool mod_delayed_work(struct workqueue_struct *wq,
}

/**
+ * queue_rcu_work - queue work on a workqueue after a RCU grace period
+ * @wq: workqueue to use
+ * @rwork: RCU work to queue
+ *
+ * Equivalent to queue_rcu_work_on() but tries to use the local CPU.
+ */
+static inline bool queue_rcu_work(struct workqueue_struct *wq,
+ struct rcu_work *rwork)
+{
+ return queue_rcu_work_on(WORK_CPU_UNBOUND, wq, rwork);
+}
+
+/**
* schedule_work_on - put work task on a specific cpu
* @cpu: cpu to put the work task on
* @work: job to be done
diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index 8cda3bc..4c5d4ca0 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -4514,10 +4514,10 @@ static struct cftype cgroup_base_files[] = {
* and thus involve punting to css->destroy_work adding two additional
* steps to the already complex sequence.
*/
-static void css_free_work_fn(struct work_struct *work)
+static void css_free_rwork_fn(struct work_struct *work)
{
- struct cgroup_subsys_state *css =
- container_of(work, struct cgroup_subsys_state, destroy_work);
+ struct cgroup_subsys_state *css = container_of(to_rcu_work(work),
+ struct cgroup_subsys_state, destroy_rwork);
struct cgroup_subsys *ss = css->ss;
struct cgroup *cgrp = css->cgroup;

@@ -4563,15 +4563,6 @@ static void css_free_work_fn(struct work_struct *work)
}
}

-static void css_free_rcu_fn(struct rcu_head *rcu_head)
-{
- struct cgroup_subsys_state *css =
- container_of(rcu_head, struct cgroup_subsys_state, rcu_head);
-
- INIT_WORK(&css->destroy_work, css_free_work_fn);
- queue_work(cgroup_destroy_wq, &css->destroy_work);
-}
-
static void css_release_work_fn(struct work_struct *work)
{
struct cgroup_subsys_state *css =
@@ -4621,7 +4612,8 @@ static void css_release_work_fn(struct work_struct *work)

mutex_unlock(&cgroup_mutex);

- call_rcu(&css->rcu_head, css_free_rcu_fn);
+ INIT_RCU_WORK(&css->destroy_rwork, css_free_rwork_fn);
+ queue_rcu_work(cgroup_destroy_wq, &css->destroy_rwork);
}

static void css_release(struct percpu_ref *ref)
@@ -4755,7 +4747,8 @@ static struct cgroup_subsys_state *css_create(struct cgroup *cgrp,
err_list_del:
list_del_rcu(&css->sibling);
err_free_css:
- call_rcu(&css->rcu_head, css_free_rcu_fn);
+ INIT_RCU_WORK(&css->destroy_rwork, css_free_rwork_fn);
+ queue_rcu_work(cgroup_destroy_wq, &css->destroy_rwork);
return ERR_PTR(err);
}

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index bb9a519..e26c2f4 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -1604,6 +1604,40 @@ bool mod_delayed_work_on(int cpu, struct workqueue_struct *wq,
}
EXPORT_SYMBOL_GPL(mod_delayed_work_on);

+static void rcu_work_rcufn(struct rcu_head *rcu)
+{
+ struct rcu_work *rwork = container_of(rcu, struct rcu_work, rcu);
+
+ /* read the comment in __queue_work() */
+ local_irq_disable();
+ __queue_work(rwork->cpu, rwork->wq, &rwork->work);
+ local_irq_enable();
+}
+
+/**
+ * queue_rcu_work_on - queue work on specific CPU after a RCU grace period
+ * @cpu: CPU number to execute work on
+ * @wq: workqueue to use
+ * @rwork: work to queue
+ *
+ * Return: %false if @work was already on a queue, %true otherwise.
+ */
+bool queue_rcu_work_on(int cpu, struct workqueue_struct *wq,
+ struct rcu_work *rwork)
+{
+ struct work_struct *work = &rwork->work;
+
+ if (!test_and_set_bit(WORK_STRUCT_PENDING_BIT, work_data_bits(work))) {
+ rwork->wq = wq;
+ rwork->cpu = cpu;
+ call_rcu(&rwork->rcu, rcu_work_rcufn);
+ return true;
+ }
+
+ return false;
+}
+EXPORT_SYMBOL(queue_rcu_work_on);
+
/**
* worker_enter_idle - enter idle state
* @worker: worker which is entering idle state
@@ -3001,6 +3035,26 @@ bool flush_delayed_work(struct delayed_work *dwork)
}
EXPORT_SYMBOL(flush_delayed_work);

+/**
+ * flush_rcu_work - wait for a rwork to finish executing the last queueing
+ * @rwork: the rcu work to flush
+ *
+ * Return:
+ * %true if flush_rcu_work() waited for the work to finish execution,
+ * %false if it was already idle.
+ */
+bool flush_rcu_work(struct rcu_work *rwork)
+{
+ if (test_bit(WORK_STRUCT_PENDING_BIT, work_data_bits(&rwork->work))) {
+ rcu_barrier();
+ flush_work(&rwork->work);
+ return true;
+ } else {
+ return flush_work(&rwork->work);
+ }
+}
+EXPORT_SYMBOL(flush_rcu_work);
+
static bool __cancel_work(struct work_struct *work, bool is_dwork)
{
unsigned long flags;
--
2.9.5
\
 
 \ /
  Last update: 2018-03-06 18:37    [W:0.184 / U:0.600 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site