elevator: Fix a race in elevator switching
There's a race between elevator switching and normal io operation.
Because the allocation of struct elevator_queue and struct elevator_data
don't in a atomic operation.So there are have chance to use NULL
->elevator_data.
For example:
Thread A: Thread B
blk_queu_bio elevator_switch
spin_lock_irq(q->queue_block) elevator_alloc
elv_merge elevator_init_fn
Because call elevator_alloc, it can't hold queue_lock and the
->elevator_data is NULL.So at the same time, threadA call elv_merge and
nedd some info of elevator_data.So the crash happened.
Move the elevator_alloc into func elevator_init_fn, it make the
operations in a atomic operation.
Using the follow method can easy reproduce this bug
1:dd if=/dev/sdb of=/dev/null
2:while true;do echo noop > scheduler;echo deadline > scheduler;done
The test method also use this method.
Signed-off-by: Jianpeng Ma <majianpeng@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/include/linux/elevator.h b/include/linux/elevator.h
index acd0312..306dd8c 100644
--- a/include/linux/elevator.h
+++ b/include/linux/elevator.h
@@ -7,6 +7,7 @@
#ifdef CONFIG_BLOCK
struct io_cq;
+struct elevator_type;
typedef int (elevator_merge_fn) (struct request_queue *, struct request **,
struct bio *);
@@ -35,7 +36,8 @@
typedef void (elevator_activate_req_fn) (struct request_queue *, struct request *);
typedef void (elevator_deactivate_req_fn) (struct request_queue *, struct request *);
-typedef int (elevator_init_fn) (struct request_queue *);
+typedef int (elevator_init_fn) (struct request_queue *,
+ struct elevator_type *e);
typedef void (elevator_exit_fn) (struct elevator_queue *);
struct elevator_ops
@@ -155,6 +157,8 @@
extern void elevator_exit(struct elevator_queue *);
extern int elevator_change(struct request_queue *, const char *);
extern bool elv_rq_merge_ok(struct request *, struct bio *);
+extern struct elevator_queue *elevator_alloc(struct request_queue *,
+ struct elevator_type *);
/*
* Helper functions.