Re: [PATCH 2/2] block: fix accounting bug on cross partition merges

[Jens Axboe <jaxboe@fusionio.com>]

On 2011-01-04 22:00, Greg KH wrote:
> On Tue, Jan 04, 2011 at 04:55:13PM +0100, Jerome Marchand wrote:
>> Also add a refcount to struct hd_struct to keep the partition in
>> memory as long as users exist. We use kref_test_and_get() to ensure
>> we don't add a reference to a partition which is going away.
> 
> No, don't do this, use a kref correctly and no such function should be
> needed.
> 
>> +	} else {
>> +		part = disk_map_sector_rcu(rq->rq_disk, blk_rq_pos(rq));
> 
> That is the function that should properly increment the reference count
> on the object.  If the object is "being removed", then it will return
> NULL and you need to check that.  Do that and you do not need to add:

It doesn't matter if you do it in there of after the fact, since the
"lock" (RCU) is being held across the call. See my original suggestion
here:

https://lkml.org/lkml/2010/12/17/275

-- 
Jens Axboe