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-rw-r--r--block/blk-ioc.c99
1 files changed, 66 insertions, 33 deletions
diff --git a/block/blk-ioc.c b/block/blk-ioc.c
index 8bebf06..b13ed96 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)
{
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