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block: do not allow updates through sysfs until registration completes 

When a new disk shows up, sysfs queue directory is created before elevator
is registered. This allows a user to attempt a scheduler switch even though
the initial registration hasn't completed yet.

In one scenario, blk_register_queue() calls elv_register_queue() and
right before cfq_registered_queue() is called, another process executes
elevator_switch() and replaces q->elevator with deadline scheduler. When
cfq_registered_queue() executes it interprets e->elevator_data as struct
cfq_data even though it is actually struct deadline_data.

Grab q->sysfs_lock in blk_register_queue() to synchronize with sysfs
callers.

Signed-off-by: Tahsin Erdogan <tahsin@google.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
This commit is contained in:
Tahsin Erdogan 2017-02-14 19:27:38 -08:00 committed by Jens Axboe
parent 3d492c2e01
commit b410aff2bd
1 changed files with 12 additions and 7 deletions
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21
block/blk-sysfs.c
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@ -902,17 +902,20 @@ int blk_register_queue(struct gendisk *disk)
if (ret)
return ret;
if (q->mq_ops)
blk_mq_register_dev(dev, q);
/* Prevent changes through sysfs until registration is completed. */
mutex_lock(&q->sysfs_lock);
ret = kobject_add(&q->kobj, kobject_get(&dev->kobj), "%s", "queue");
if (ret < 0) {
blk_trace_remove_sysfs(dev);
return ret;
goto unlock;
}
kobject_uevent(&q->kobj, KOBJ_ADD);
if (q->mq_ops)
blk_mq_register_dev(dev, q);
blk_wb_init(q);
if (q->request_fn || (q->mq_ops && q->elevator)) {
@ -922,11 +925,13 @@ int blk_register_queue(struct gendisk *disk)
kobject_del(&q->kobj);
blk_trace_remove_sysfs(dev);
kobject_put(&dev->kobj);
goto unlock;
}
}
ret = 0;
unlock:
mutex_unlock(&q->sysfs_lock);
return ret;
}
}
return 0;
}
void blk_unregister_queue(struct gendisk *disk)