d50235b7bc
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>
125 lines
2.7 KiB
C
125 lines
2.7 KiB
C
/*
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* elevator noop
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*/
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#include <linux/blkdev.h>
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#include <linux/elevator.h>
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#include <linux/bio.h>
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#include <linux/module.h>
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#include <linux/slab.h>
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#include <linux/init.h>
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struct noop_data {
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struct list_head queue;
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};
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static void noop_merged_requests(struct request_queue *q, struct request *rq,
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struct request *next)
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{
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list_del_init(&next->queuelist);
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}
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static int noop_dispatch(struct request_queue *q, int force)
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{
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struct noop_data *nd = q->elevator->elevator_data;
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if (!list_empty(&nd->queue)) {
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struct request *rq;
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rq = list_entry(nd->queue.next, struct request, queuelist);
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list_del_init(&rq->queuelist);
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elv_dispatch_sort(q, rq);
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return 1;
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}
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return 0;
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}
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static void noop_add_request(struct request_queue *q, struct request *rq)
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{
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struct noop_data *nd = q->elevator->elevator_data;
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list_add_tail(&rq->queuelist, &nd->queue);
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}
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static struct request *
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noop_former_request(struct request_queue *q, struct request *rq)
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{
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struct noop_data *nd = q->elevator->elevator_data;
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if (rq->queuelist.prev == &nd->queue)
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return NULL;
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return list_entry(rq->queuelist.prev, struct request, queuelist);
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}
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static struct request *
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noop_latter_request(struct request_queue *q, struct request *rq)
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{
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struct noop_data *nd = q->elevator->elevator_data;
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if (rq->queuelist.next == &nd->queue)
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return NULL;
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return list_entry(rq->queuelist.next, struct request, queuelist);
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}
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static int noop_init_queue(struct request_queue *q, struct elevator_type *e)
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{
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struct noop_data *nd;
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struct elevator_queue *eq;
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eq = elevator_alloc(q, e);
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if (!eq)
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return -ENOMEM;
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nd = kmalloc_node(sizeof(*nd), GFP_KERNEL, q->node);
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if (!nd) {
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kobject_put(&eq->kobj);
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return -ENOMEM;
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}
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eq->elevator_data = nd;
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INIT_LIST_HEAD(&nd->queue);
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spin_lock_irq(q->queue_lock);
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q->elevator = eq;
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spin_unlock_irq(q->queue_lock);
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return 0;
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}
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static void noop_exit_queue(struct elevator_queue *e)
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{
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struct noop_data *nd = e->elevator_data;
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BUG_ON(!list_empty(&nd->queue));
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kfree(nd);
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}
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static struct elevator_type elevator_noop = {
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.ops = {
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.elevator_merge_req_fn = noop_merged_requests,
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.elevator_dispatch_fn = noop_dispatch,
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.elevator_add_req_fn = noop_add_request,
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.elevator_former_req_fn = noop_former_request,
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.elevator_latter_req_fn = noop_latter_request,
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.elevator_init_fn = noop_init_queue,
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.elevator_exit_fn = noop_exit_queue,
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},
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.elevator_name = "noop",
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.elevator_owner = THIS_MODULE,
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};
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static int __init noop_init(void)
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{
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return elv_register(&elevator_noop);
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}
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static void __exit noop_exit(void)
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{
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elv_unregister(&elevator_noop);
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}
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module_init(noop_init);
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module_exit(noop_exit);
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MODULE_AUTHOR("Jens Axboe");
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MODULE_LICENSE("GPL");
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MODULE_DESCRIPTION("No-op IO scheduler");
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