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Subject[GIT PULL] single block fix for 2.6.36
Hi Linus,

The API that was added for drivers to switch IO schedulers
when loaded does not work if the driver isn't in a fully
initialized state. The in-kernel ones call it right after
blk_init_queue(), which will result in an oops when the
elevator core tries to unregister unregistered kobjects.

Add a registered bit and only do the unregister/register
dance in elevator_switch() if we need to. The other call
path for this is the sysfs parts to allow online switching,
which can only be called with a fully setup driver.

Please pull, this is a regression introduced in this series.

are available in the git repository at:
git://git.kernel.dk/linux-2.6-block.git for-linus

Jens Axboe (1):
elevator: fix oops on early call to elevator_change()

block/elevator.c | 12 ++++++++----
include/linux/elevator.h | 1 +
2 files changed, 9 insertions(+), 4 deletions(-)
diff --git a/block/elevator.c b/block/elevator.c
index 205b09a..4e11559 100644
--- a/block/elevator.c
+++ b/block/elevator.c
@@ -938,6 +938,7 @@ int elv_register_queue(struct request_queue *q)
}
}
kobject_uevent(&e->kobj, KOBJ_ADD);
+ e->registered = 1;
}
return error;
}
@@ -947,6 +948,7 @@ static void __elv_unregister_queue(struct elevator_queue *e)
{
kobject_uevent(&e->kobj, KOBJ_REMOVE);
kobject_del(&e->kobj);
+ e->registered = 0;
}

void elv_unregister_queue(struct request_queue *q)
@@ -1042,11 +1044,13 @@ static int elevator_switch(struct request_queue *q, struct elevator_type *new_e)

spin_unlock_irq(q->queue_lock);

- __elv_unregister_queue(old_elevator);
+ if (old_elevator->registered) {
+ __elv_unregister_queue(old_elevator);

- err = elv_register_queue(q);
- if (err)
- goto fail_register;
+ err = elv_register_queue(q);
+ if (err)
+ goto fail_register;
+ }

/*
* finally exit old elevator and turn off BYPASS.
diff --git a/include/linux/elevator.h b/include/linux/elevator.h
index 926b503..4fd978e 100644
--- a/include/linux/elevator.h
+++ b/include/linux/elevator.h
@@ -93,6 +93,7 @@ struct elevator_queue
struct elevator_type *elevator_type;
struct mutex sysfs_lock;
struct hlist_head *hash;
+ unsigned int registered:1;
};

/*
--
Jens Axboe



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