block, cfq: replace current_io_context() with create_io_context()

When called under queue_lock, current_io_context() triggers lockdep
warning if it hits allocation path.  This is because io_context
installation is protected by task_lock which is not IRQ safe, so it
triggers irq-unsafe-lock -> irq -> irq-safe-lock -> irq-unsafe-lock
deadlock warning.

Given the restriction, accessor + creator rolled into one doesn't work
too well.  Drop current_io_context() and let the users access
task->io_context directly inside queue_lock combined with explicit
creation using create_io_context().

Future ioc updates will further consolidate ioc access and the create
interface will be unexported.

While at it, relocate ioc internal interface declarations in blk.h and
add section comments before and after.

This patch does not introduce functional change.

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 33 insertions, 3 deletions

diff --git a/block/blk.h b/block/blk.h
index 8d421156fefb..5bca2668e1bf 100644
--- a/block/blk.h
+++ b/block/blk.h
@@ -127,9 +127,6 @@ 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,
                      struct bio *bio);
 int ll_front_merge_fn(struct request_queue *q, struct request *req, 
@@ -198,6 +195,39 @@ static inline int blk_do_io_stat(struct request *rq)
                 (rq->cmd_flags & REQ_DISCARD));
 }
 
+/*
+ * Internal io_context interface
+ */
+void get_io_context(struct io_context *ioc);
+
+void create_io_context_slowpath(struct task_struct *task, gfp_t gfp_mask,
+                                int node);
+
+/**
+ * create_io_context - try to create task->io_context
+ * @task: target task
+ * @gfp_mask: allocation mask
+ * @node: allocation node
+ *
+ * If @task->io_context is %NULL, allocate a new io_context and install it.
+ * Returns the current @task->io_context which may be %NULL if allocation
+ * failed.
+ *
+ * Note that this function can't be called with IRQ disabled because
+ * task_lock which protects @task->io_context is IRQ-unsafe.
+ */
+static inline struct io_context *create_io_context(struct task_struct *task,
+                                                   gfp_t gfp_mask, int node)
+{
+        WARN_ON_ONCE(irqs_disabled());
+        if (unlikely(!task->io_context))
+                create_io_context_slowpath(task, gfp_mask, node);
+        return task->io_context;
+}
+
+/*
+ * Internal throttling interface
+ */
 #ifdef CONFIG_BLK_DEV_THROTTLING
 extern bool blk_throtl_bio(struct request_queue *q, struct bio *bio);
 extern void blk_throtl_drain(struct request_queue *q);