[PATCHSET] blkcg: update locking and fix stacking

Currently ioc->nr_tasks is used to decide two things - whether an ioc
is done issuing IOs and whether it's shared by multiple tasks. This
patch separate out the first into ioc->active_ref, which is acquired
and released using {get|put}_io_context_active() respectively.

This will be used to associate bio's with a given task. This patch
doesn't introduce any visible behavior change.

Signed-off-by: Tejun Heo
Cc: Vivek Goyal

block/blk-ioc.c | 36 +++++++++++++++++++++++++--
block/cfq-iosched.c | 4 ++--
include/linux/iocontext.h | 22 ++++++++++++++++++++--
3 files changed, 47 insertions(+), 15 deletions(-)

diff --git a/block/blk-ioc.c b/block/blk-ioc.c
index 1092874..439ec21 100644
a/block/blk-ioc.c
+++ b/block/blk-ioc.c
@@ -149,20 +149,20 @@ void put_io_context(struct io_context *ioc)
}
EXPORT_SYMBOL(put_io_context);

-/* Called by the exiting task */
-void exit_io_context(struct task_struct *task)
+/**
+ * put_io_context_active - put active reference on ioc
+ * @ioc: ioc of interest
+ *
+ * Undo get_io_context_active(). If active reference reaches zero after
+ * put, @ioc can never issue further IOs and ioscheds are notified.
+ */
+void put_io_context_active(struct io_context *ioc)
{
- struct io_context *ioc;
- struct io_cq *icq;
struct hlist_node *n;
unsigned long flags;
+ struct io_cq *icq;

- task_lock(task);
- ioc = task->io_context;
- task->io_context = NULL;
- task_unlock(task);
-
- if (!atomic_dec_and_test(&ioc->nr_tasks)) {
+ if (!atomic_dec_and_test(&ioc->active_ref)) {
put_io_context(ioc);
return;
}
@@ -191,6 +191,20 @@ retry:
put_io_context(ioc);
}

+/* Called by the exiting task */
+void exit_io_context(struct task_struct *task)
+{
+ struct io_context *ioc;
+
+ task_lock(task);
+ ioc = task->io_context;
+ task->io_context = NULL;
+ task_unlock(task);
+
+ atomic_dec(&ioc->nr_tasks);
+ put_io_context_active(ioc);
+}
+
/**
* ioc_clear_queue - break any ioc association with the specified queue
* @q: request_queue being cleared
@@ -223,7 +237,7 @@ int create_task_io_context(struct task_struct *task, gfp_t gfp_flags, int node)

/* initialize */
atomic_long_set(&ioc->refcount, 1);
- atomic_set(&ioc->nr_tasks, 1);
+ atomic_set(&ioc->active_ref, 1);
spin_lock_init(&ioc->lock);
INIT_RADIX_TREE(&ioc->icq_tree, GFP_ATOMIC | __GFP_HIGH);
INIT_HLIST_HEAD(&ioc->icq_list);
diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index cc8e9ef..00e28a3 100644
a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -1865,7 +1865,7 @@ static void cfq_arm_slice_timer(struct cfq_data *cfqd)
* task has exited, don't wait
*/
cic = cfqd->active_cic;
- if (!cic || !atomic_read(&cic->icq.ioc->nr_tasks))
+ if (!cic || !atomic_read(&cic->icq.ioc->active_ref))
return;

/*
@@ -2841,7 +2841,7 @@ cfq_update_idle_window(struct cfq_data *cfqd, struct cfq_queue *cfqq,

if (cfqq->next_rq && (cfqq->next_rq->cmd_flags & REQ_NOIDLE))
enable_idle = 0;
- else if (!atomic_read(&cic->icq.ioc->nr_tasks) ||
+ else if (!atomic_read(&cic->icq.ioc->active_ref) ||
!cfqd->cfq_slice_idle ||
(!cfq_cfqq_deep(cfqq) && CFQQ_SEEKY(cfqq)))
enable_idle = 0;
diff --git a/include/linux/iocontext.h b/include/linux/iocontext.h
index 81a8870..6f1a260 100644
a/include/linux/iocontext.h
+++ b/include/linux/iocontext.h
@@ -100,6 +100,7 @@ struct io_cq {
*/
struct io_context {
atomic_long_t refcount;
+ atomic_t active_ref;
atomic_t nr_tasks;

/* all the fields below are protected by this lock */
@@ -120,17 +121,34 @@ struct io_context {
struct work_struct release_work;
};

-static inline void ioc_task_link(struct io_context *ioc)
+/**
+ * get_io_context_active - get active reference on ioc
+ * @ioc: ioc of interest
+ *
+ * Only iocs with active reference can issue new IOs. This function
+ * acquires an active reference on @ioc. The caller must already have an
+ * active reference on @ioc.
+ */
+static inline void get_io_context_active(struct io_context *ioc)
{
WARN_ON_ONCE(atomic_long_read(&ioc->refcount) <= 0);
- WARN_ON_ONCE(atomic_read(&ioc->nr_tasks) <= 0);
+ WARN_ON_ONCE(atomic_read(&ioc->active_ref) <= 0);
atomic_long_inc(&ioc->refcount);
+ atomic_inc(&ioc->active_ref);
+}
+
+static inline void ioc_task_link(struct io_context *ioc)
+{
+ get_io_context_active(ioc);
+
+ WARN_ON_ONCE(atomic_read(&ioc->nr_tasks) <= 0);
atomic_inc(&ioc->nr_tasks);
}

struct task_struct;
#ifdef CONFIG_BLOCK
void put_io_context(struct io_context *ioc);
+void put_io_context_active(struct io_context *ioc);
void exit_io_context(struct task_struct *task);
struct io_context *get_task_io_context(struct task_struct *task,
gfp_t gfp_flags, int node);
1.7.7.3

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