Messages in this thread | | | Date | Wed, 5 Jan 2011 15:17:45 +0100 | From | Jens Axboe <> | Subject | Re: [PATCH 2/2] block: fix accounting bug on cross partition merges |
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On 2011-01-05 15:09, Jerome Marchand wrote: > On 01/05/2011 03:00 PM, Jens Axboe wrote: >> On 2011-01-04 16:55, Jerome Marchand wrote: >>> + } else { >>> + part = disk_map_sector_rcu(rq->rq_disk, blk_rq_pos(rq)); >>> + if (!kref_test_and_get(&part->ref)) { >>> + /* >>> + * The partition is already being removed, >>> + * the request will be accounted on the disk only >>> + * >>> + * We take a reference on disk->part0 although that >>> + * partition will never be deleted, so we can treat >>> + * it as any other partition. >>> + */ >>> + part = &rq->rq_disk->part0; >>> + kref_get(&part->ref); >>> + } >> >> This still doesn't work. So you are inside the if {} block, you know >> what someone has dropped the last reference and the call_rcu() is being >> scheduled. Adding a reference now will not prevent 'part' from going >> away as soon as you do part_stat_unlock(). > > And what is the problem with that since we don't use 'part' (as returned > by disk_map_sector_rcu()), but disk->part0 instead?
Ugh, I'm the one who's blind now. part0 is indeed fine, I didn't read that carefully enough.
So I think your patch looks safe now, I don't see any holes in it. Whether we move the kref to inside the lookup or not, that doesn't change anything wrt using an atomic_inc_not_zero(). Can you resend 1/2 with the manual barriers removed?
-- Jens Axboe
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