diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index 8f630cec906e8..4b001dcd85b0d 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -1645,11 +1645,12 @@ static void blkiocg_attach_task(struct cgroup *cgrp, struct task_struct *tsk)
{
struct io_context *ioc;
- task_lock(tsk);
- ioc = tsk->io_context;
- if (ioc)
+ /* we don't lose anything even if ioc allocation fails */
+ ioc = get_task_io_context(tsk, GFP_ATOMIC, NUMA_NO_NODE);
+ if (ioc) {
ioc->cgroup_changed = 1;
- task_unlock(tsk);
+ put_io_context(ioc);
+ }
}
void blkio_policy_register(struct blkio_policy_type *blkiop)
diff --git a/block/blk-ioc.c b/block/blk-ioc.c
index 8bebf06bac76c..b13ed96776c29 100644
--- a/block/blk-ioc.c
+++ b/block/blk-ioc.c
@@ -16,6 +16,19 @@
*/
static struct kmem_cache *iocontext_cachep;
+/**
+ * get_io_context - increment reference count to io_context
+ * @ioc: io_context to get
+ *
+ * Increment reference count to @ioc.
+ */
+void get_io_context(struct io_context *ioc)
+{
+ BUG_ON(atomic_long_read(&ioc->refcount) <= 0);
+ atomic_long_inc(&ioc->refcount);
+}
+EXPORT_SYMBOL(get_io_context);
+
static void cfq_dtor(struct io_context *ioc)
{
if (!hlist_empty(&ioc->cic_list)) {
@@ -71,6 +84,9 @@ void exit_io_context(struct task_struct *task)
{
struct io_context *ioc;
+ /* PF_EXITING prevents new io_context from being attached to @task */
+ WARN_ON_ONCE(!(current->flags & PF_EXITING));
+
task_lock(task);
ioc = task->io_context;
task->io_context = NULL;
@@ -82,7 +98,9 @@ void exit_io_context(struct task_struct *task)
put_io_context(ioc);
}
-struct io_context *alloc_io_context(gfp_t gfp_flags, int node)
+static struct io_context *create_task_io_context(struct task_struct *task,
+ gfp_t gfp_flags, int node,
+ bool take_ref)
{
struct io_context *ioc;
@@ -98,6 +116,20 @@ struct io_context *alloc_io_context(gfp_t gfp_flags, int node)
INIT_RADIX_TREE(&ioc->radix_root, GFP_ATOMIC | __GFP_HIGH);
INIT_HLIST_HEAD(&ioc->cic_list);
+ /* try to install, somebody might already have beaten us to it */
+ task_lock(task);
+
+ if (!task->io_context && !(task->flags & PF_EXITING)) {
+ task->io_context = ioc;
+ } else {
+ kmem_cache_free(iocontext_cachep, ioc);
+ ioc = task->io_context;
+ }
+
+ if (ioc && take_ref)
+ get_io_context(ioc);
+
+ task_unlock(task);
return ioc;
}
@@ -114,46 +146,47 @@ struct io_context *alloc_io_context(gfp_t gfp_flags, int node)
*/
struct io_context *current_io_context(gfp_t gfp_flags, int node)
{
- struct task_struct *tsk = current;
- struct io_context *ret;
-
- ret = tsk->io_context;
- if (likely(ret))
- return ret;
-
- ret = alloc_io_context(gfp_flags, node);
- if (ret) {
- /* make sure set_task_ioprio() sees the settings above */
- smp_wmb();
- tsk->io_context = ret;
- }
+ might_sleep_if(gfp_flags & __GFP_WAIT);
- return ret;
+ if (current->io_context)
+ return current->io_context;
+
+ return create_task_io_context(current, gfp_flags, node, false);
}
+EXPORT_SYMBOL(current_io_context);
-/*
- * If the current task has no IO context then create one and initialise it.
- * If it does have a context, take a ref on it.
+/**
+ * get_task_io_context - get io_context of a task
+ * @task: task of interest
+ * @gfp_flags: allocation flags, used if allocation is necessary
+ * @node: allocation node, used if allocation is necessary
+ *
+ * Return io_context of @task. If it doesn't exist, it is created with
+ * @gfp_flags and @node. The returned io_context has its reference count
+ * incremented.
*
- * This is always called in the context of the task which submitted the I/O.
+ * This function always goes through task_lock() and it's better to use
+ * current_io_context() + get_io_context() for %current.
*/
-struct io_context *get_io_context(gfp_t gfp_flags, int node)
+struct io_context *get_task_io_context(struct task_struct *task,
+ gfp_t gfp_flags, int node)
{
- struct io_context *ioc = NULL;
-
- /*
- * Check for unlikely race with exiting task. ioc ref count is
- * zero when ioc is being detached.
- */
- do {
- ioc = current_io_context(gfp_flags, node);
- if (unlikely(!ioc))
- break;
- } while (!atomic_long_inc_not_zero(&ioc->refcount));
+ struct io_context *ioc;
- return ioc;
+ might_sleep_if(gfp_flags & __GFP_WAIT);
+
+ task_lock(task);
+ ioc = task->io_context;
+ if (likely(ioc)) {
+ get_io_context(ioc);
+ task_unlock(task);
+ return ioc;
+ }
+ task_unlock(task);
+
+ return create_task_io_context(task, gfp_flags, node, true);
}
-EXPORT_SYMBOL(get_io_context);
+EXPORT_SYMBOL(get_task_io_context);
static int __init blk_ioc_init(void)
{
diff --git a/block/blk.h b/block/blk.h
index aae4d88fc523b..fc3c41b2fd24a 100644
--- a/block/blk.h
+++ b/block/blk.h
@@ -122,6 +122,7 @@ static inline int blk_should_fake_timeout(struct request_queue *q)
}
#endif
+void get_io_context(struct io_context *ioc);
struct io_context *current_io_context(gfp_t gfp_flags, int node);
int ll_back_merge_fn(struct request_queue *q, struct request *req,
diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index ec3f5e8ba564f..d42d89ccce1b1 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -14,6 +14,7 @@
#include <linux/rbtree.h>
#include <linux/ioprio.h>
#include <linux/blktrace_api.h>
+#include "blk.h"
#include "cfq.h"
/*
@@ -3194,13 +3195,13 @@ static struct cfq_io_context *
cfq_get_io_context(struct cfq_data *cfqd, gfp_t gfp_mask)
{
struct io_context *ioc = NULL;
- struct cfq_io_context *cic;
+ struct cfq_io_context *cic = NULL;
might_sleep_if(gfp_mask & __GFP_WAIT);
- ioc = get_io_context(gfp_mask, cfqd->queue->node);
+ ioc = current_io_context(gfp_mask, cfqd->queue->node);
if (!ioc)
- return NULL;
+ goto err;
cic = cfq_cic_lookup(cfqd, ioc);
if (cic)
@@ -3211,10 +3212,10 @@ cfq_get_io_context(struct cfq_data *cfqd, gfp_t gfp_mask)
goto err;
if (cfq_cic_link(cfqd, ioc, cic, gfp_mask))
- goto err_free;
-
+ goto err;
out:
- smp_read_barrier_depends();
+ get_io_context(ioc);
+
if (unlikely(ioc->ioprio_changed))
cfq_ioc_set_ioprio(ioc);
@@ -3223,10 +3224,9 @@ cfq_get_io_context(struct cfq_data *cfqd, gfp_t gfp_mask)
cfq_ioc_set_cgroup(ioc);
#endif
return cic;
-err_free:
- cfq_cic_free(cic);
err:
- put_io_context(ioc);
+ if (cic)
+ cfq_cic_free(cic);
return NULL;
}
diff --git a/fs/ioprio.c b/fs/ioprio.c
index f79dab83e17b3..998ec239d1ea2 100644
--- a/fs/ioprio.c
+++ b/fs/ioprio.c
@@ -48,28 +48,13 @@ int set_task_ioprio(struct task_struct *task, int ioprio)
if (err)
return err;
- task_lock(task);
- do {
- ioc = task->io_context;
- /* see wmb() in current_io_context() */
- smp_read_barrier_depends();
- if (ioc)
- break;
-
- ioc = alloc_io_context(GFP_ATOMIC, -1);
- if (!ioc) {
- err = -ENOMEM;
- break;
- }
- task->io_context = ioc;
- } while (1);
-
- if (!err) {
+ ioc = get_task_io_context(task, GFP_ATOMIC, NUMA_NO_NODE);
+ if (ioc) {
ioc->ioprio = ioprio;
ioc->ioprio_changed = 1;
+ put_io_context(ioc);
}
- task_unlock(task);
return err;
}
EXPORT_SYMBOL_GPL(set_task_ioprio);
diff --git a/include/linux/iocontext.h b/include/linux/iocontext.h
index 8a6ecb66346fe..28bb621ef5a2a 100644
--- a/include/linux/iocontext.h
+++ b/include/linux/iocontext.h
@@ -78,8 +78,8 @@ struct task_struct;
#ifdef CONFIG_BLOCK
void put_io_context(struct io_context *ioc);
void exit_io_context(struct task_struct *task);
-struct io_context *get_io_context(gfp_t gfp_flags, int node);
-struct io_context *alloc_io_context(gfp_t gfp_flags, int node);
+struct io_context *get_task_io_context(struct task_struct *task,
+ gfp_t gfp_flags, int node);
#else
struct io_context;
static inline void put_io_context(struct io_context *ioc) { }
diff --git a/kernel/fork.c b/kernel/fork.c
index da4a6a10d088d..5bcfc739bb7c6 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -870,6 +870,7 @@ static int copy_io(unsigned long clone_flags, struct task_struct *tsk)
{
#ifdef CONFIG_BLOCK
struct io_context *ioc = current->io_context;
+ struct io_context *new_ioc;
if (!ioc)
return 0;
@@ -881,11 +882,12 @@ static int copy_io(unsigned long clone_flags, struct task_struct *tsk)
if (unlikely(!tsk->io_context))
return -ENOMEM;
} else if (ioprio_valid(ioc->ioprio)) {
- tsk->io_context = alloc_io_context(GFP_KERNEL, -1);
- if (unlikely(!tsk->io_context))
+ new_ioc = get_task_io_context(tsk, GFP_KERNEL, NUMA_NO_NODE);
+ if (unlikely(!new_ioc))
return -ENOMEM;
- tsk->io_context->ioprio = ioc->ioprio;
+ new_ioc->ioprio = ioc->ioprio;
+ put_io_context(new_ioc);
}
#endif
return 0;