block: document blk_plug list access
I'm often confused why not disable preempt when changing blk_plug list. It
would be better to add comments here in case others have the similar concerns.
Signed-off-by: Shaohua Li <shaohua.li@intel.com>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 92edb96..6dcea68 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -857,6 +857,12 @@
struct request_queue *blk_alloc_queue_node(gfp_t, int);
extern void blk_put_queue(struct request_queue *);
+/*
+ * Note: Code in between changing the blk_plug list/cb_list or element of such
+ * lists is preemptable, but such code can't do sleep (or be very careful),
+ * otherwise data is corrupted. For details, please check schedule() where
+ * blk_schedule_flush_plug() is called.
+ */
struct blk_plug {
unsigned long magic;
struct list_head list;