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blk-mq-sched: fix crash in switch error path

Browse Source 
In elevator_switch(), if blk_mq_init_sched() fails, we attempt to fall
back to the original scheduler. However, at this point, we've already
torn down the original scheduler's tags, so this causes a crash. Doing
the fallback like the legacy elevator path is much harder for mq, so fix
it by just falling back to none, instead.

Signed-off-by: Omar Sandoval <osandov@fb.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
This commit is contained in:
Omar Sandoval 2017-04-07 08:52:27 -06:00 committed by Jens Axboe
parent 93252632e8
commit 54d5329d42
6 changed files with 67 additions and 48 deletions
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13
block/blk-mq-sched.c
View File

@ -451,7 +451,7 @@ static int blk_mq_sched_alloc_tags(struct request_queue *q,
return ret;
}
void blk_mq_sched_teardown(struct request_queue *q)
static void blk_mq_sched_tags_teardown(struct request_queue *q)
{
struct blk_mq_tag_set *set = q->tag_set;
struct blk_mq_hw_ctx *hctx;
@ -513,10 +513,19 @@ int blk_mq_init_sched(struct request_queue *q, struct elevator_type *e)
return 0;
err:
blk_mq_sched_teardown(q);
blk_mq_sched_tags_teardown(q);
q->elevator = NULL;
return ret;
}
void blk_mq_exit_sched(struct request_queue *q, struct elevator_queue *e)
{
if (e->type->ops.mq.exit_sched)
e->type->ops.mq.exit_sched(e);
blk_mq_sched_tags_teardown(q);
q->elevator = NULL;
}
int blk_mq_sched_init(struct request_queue *q)
{
int ret;

2
block/blk-mq-sched.h
View File

@ -33,7 +33,7 @@ void blk_mq_sched_move_to_dispatch(struct blk_mq_hw_ctx *hctx,
struct request *(*get_rq)(struct blk_mq_hw_ctx *));
int blk_mq_init_sched(struct request_queue *q, struct elevator_type *e);
void blk_mq_sched_teardown(struct request_queue *q);
void blk_mq_exit_sched(struct request_queue *q, struct elevator_queue *e);
int blk_mq_sched_init_hctx(struct request_queue *q, struct blk_mq_hw_ctx *hctx,
unsigned int hctx_idx);

2
block/blk-mq.c
View File

@ -2240,8 +2240,6 @@ void blk_mq_release(struct request_queue *q)
struct blk_mq_hw_ctx *hctx;
unsigned int i;
blk_mq_sched_teardown(q);
/* hctx kobj stays in hctx */
queue_for_each_hw_ctx(q, hctx, i) {
if (!hctx)

2
block/blk-sysfs.c
View File

@ -816,7 +816,7 @@ static void blk_release_queue(struct kobject *kobj)
if (q->elevator) {
ioc_clear_queue(q);
elevator_exit(q->elevator);
elevator_exit(q, q->elevator);
}
blk_exit_rl(&q->root_rl);

94
block/elevator.c
View File

@ -252,11 +252,11 @@ int elevator_init(struct request_queue *q, char *name)
}
EXPORT_SYMBOL(elevator_init);
void elevator_exit(struct elevator_queue *e)
void elevator_exit(struct request_queue *q, struct elevator_queue *e)
{
mutex_lock(&e->sysfs_lock);
if (e->uses_mq && e->type->ops.mq.exit_sched)
e->type->ops.mq.exit_sched(e);
blk_mq_exit_sched(q, e);
else if (!e->uses_mq && e->type->ops.sq.elevator_exit_fn)
e->type->ops.sq.elevator_exit_fn(e);
mutex_unlock(&e->sysfs_lock);
@ -941,6 +941,45 @@ void elv_unregister(struct elevator_type *e)
}
EXPORT_SYMBOL_GPL(elv_unregister);
static int elevator_switch_mq(struct request_queue *q,
struct elevator_type *new_e)
{
int ret;
blk_mq_freeze_queue(q);
blk_mq_quiesce_queue(q);
if (q->elevator) {
if (q->elevator->registered)
elv_unregister_queue(q);
ioc_clear_queue(q);
elevator_exit(q, q->elevator);
}
ret = blk_mq_init_sched(q, new_e);
if (ret)
goto out;
if (new_e) {
ret = elv_register_queue(q);
if (ret) {
elevator_exit(q, q->elevator);
goto out;
}
}
if (new_e)
blk_add_trace_msg(q, "elv switch: %s", new_e->elevator_name);
else
blk_add_trace_msg(q, "elv switch: none");
out:
blk_mq_unfreeze_queue(q);
blk_mq_start_stopped_hw_queues(q, true);
return ret;
}
/*
* switch to new_e io scheduler. be careful not to introduce deadlocks -
* we don't free the old io scheduler, before we have allocated what we
@ -953,10 +992,8 @@ static int elevator_switch(struct request_queue *q, struct elevator_type *new_e)
bool old_registered = false;
int err;
if (q->mq_ops) {
blk_mq_freeze_queue(q);
blk_mq_quiesce_queue(q);
}
if (q->mq_ops)
return elevator_switch_mq(q, new_e);
/*
* Turn on BYPASS and drain all requests w/ elevator private data.
@ -968,11 +1005,7 @@ static int elevator_switch(struct request_queue *q, struct elevator_type *new_e)
if (old) {
old_registered = old->registered;
if (old->uses_mq)
blk_mq_sched_teardown(q);
if (!q->mq_ops)
blk_queue_bypass_start(q);
blk_queue_bypass_start(q);
/* unregister and clear all auxiliary data of the old elevator */
if (old_registered)
@ -982,53 +1015,32 @@ static int elevator_switch(struct request_queue *q, struct elevator_type *new_e)
}
/* allocate, init and register new elevator */
if (q->mq_ops)
err = blk_mq_init_sched(q, new_e);
else
err = new_e->ops.sq.elevator_init_fn(q, new_e);
err = new_e->ops.sq.elevator_init_fn(q, new_e);
if (err)
goto fail_init;
if (new_e) {
err = elv_register_queue(q);
if (err)
goto fail_register;
}
err = elv_register_queue(q);
if (err)
goto fail_register;
/* done, kill the old one and finish */
if (old) {
elevator_exit(old);
if (!q->mq_ops)
blk_queue_bypass_end(q);
elevator_exit(q, old);
blk_queue_bypass_end(q);
}
if (q->mq_ops) {
blk_mq_unfreeze_queue(q);
blk_mq_start_stopped_hw_queues(q, true);
}
if (new_e)
blk_add_trace_msg(q, "elv switch: %s", new_e->elevator_name);
else
blk_add_trace_msg(q, "elv switch: none");
blk_add_trace_msg(q, "elv switch: %s", new_e->elevator_name);
return 0;
fail_register:
if (q->mq_ops)
blk_mq_sched_teardown(q);
elevator_exit(q->elevator);
elevator_exit(q, q->elevator);
fail_init:
/* switch failed, restore and re-register old elevator */
if (old) {
q->elevator = old;
elv_register_queue(q);
if (!q->mq_ops)
blk_queue_bypass_end(q);
}
if (q->mq_ops) {
blk_mq_unfreeze_queue(q);
blk_mq_start_stopped_hw_queues(q, true);
blk_queue_bypass_end(q);
}
return err;

2
include/linux/elevator.h
View File

@ -211,7 +211,7 @@ extern ssize_t elv_iosched_show(struct request_queue *, char *);
extern ssize_t elv_iosched_store(struct request_queue *, const char *, size_t);
extern int elevator_init(struct request_queue *, char *);
extern void elevator_exit(struct elevator_queue *);
extern void elevator_exit(struct request_queue *, struct elevator_queue *);
extern int elevator_change(struct request_queue *, const char *);
extern bool elv_bio_merge_ok(struct request *, struct bio *);
extern struct elevator_queue *elevator_alloc(struct request_queue *,