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SubjectRe: [PATCH] block: fix accounting bug on cross partition merges
On 12/23/2010 04:39 PM, Vivek Goyal wrote:
>> diff --git a/block/blk-core.c b/block/blk-core.c
>> index 4ce953f..72d12d2 100644
>> --- a/block/blk-core.c
>> +++ b/block/blk-core.c
>> @@ -64,13 +64,21 @@ static void drive_stat_acct(struct request *rq, int new_io)
>> return;
>>
>> cpu = part_stat_lock();
>> - part = disk_map_sector_rcu(rq->rq_disk, blk_rq_pos(rq));
>>
>> - if (!new_io)
>> + if (!new_io) {
>> + part = rq->part;
>> part_stat_inc(cpu, part, merges[rw]);
>> - else {
>> + } else {
>> + part = disk_map_sector_rcu(rq->rq_disk, blk_rq_pos(rq));
>> + if(part->partno && !kref_test_and_get(&part->ref))
>> + /*
>
> Do we have to check this part->partno both while taking and releasing
> reference. Can't we take one extra reference for disk->part0, at
> alloc_disk_node() time so that it is never freed and only freed when
> disk is going away and gendisk is being freed.
>
> That way, you don't have to differentiate between disk->part0 and rest
> of the partitions while taking or dropping references.

We could do it in any way, as long as we don't end up trying to free
disk->part0. I choose not to touch part0->ref at all, but we could also
drop all the part->partno test, and get a reference on part0 when we use
it as a backup. I have no strong opinion about a way or an other.

Jerome

>
> Thanks
> Vivek


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