On Wed, Aug 8, 2012 at 3:37 PM, Josef Bacik <jba...@fusionio.com> wrote:
> On Wed, Aug 08, 2012 at 01:49:06PM -0600, Arne Jansen wrote:
>> run_clustered_refs runs all delayed refs for one head one by one. During
>> the runs, the delayed_refs->lock is released. In this window, the ref_mod
>> from the head does not match the sum of all refs below the head. When
>> btrfs_lookup_extent_info is run in this window, it gives inconsistent
>> results.
>> The qgroups patch added code to put delayed refs back, thus opening this
>> window very wide.
>> This patch assures that head->ref_mod always matches the queued refs, but
>> a window still remains where on-disk refs + delayed_refs miss the ref
>> currently being run.
>>
>> Signed-off-by: Arne Jansen <sensi...@gmx.net>
>> ---
>> fs/btrfs/extent-tree.c | 17 +++++++++++++++++
>> 1 files changed, 17 insertions(+), 0 deletions(-)
>>
>> diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
>> index e66dc9a..60d175a 100644
>> --- a/fs/btrfs/extent-tree.c
>> +++ b/fs/btrfs/extent-tree.c
>> @@ -2318,6 +2318,23 @@ static noinline int run_clustered_refs(struct
>> btrfs_trans_handle *trans,
>> ref->in_tree = 0;
>> rb_erase(&ref->rb_node, &delayed_refs->root);
>> delayed_refs->num_entries--;
>> + if (locked_ref) {
>> + /*
>> + * when we play the delayed ref, also correct the
>> + * ref_mod on head
>> + */
>> + switch (ref->action) {
>> + case BTRFS_ADD_DELAYED_REF:
>> + case BTRFS_ADD_DELAYED_EXTENT:
>> + locked_ref->node.ref_mod -= ref->ref_mod;
>> + break;
>> + case BTRFS_DROP_DELAYED_REF:
>> + locked_ref->node.ref_mod += ref->ref_mod;
>> + break;
>> + default:
>> + WARN_ON(1);
>> + }
>> + }
>> spin_unlock(&delayed_refs->lock);
>>
>> ret = run_one_delayed_ref(trans, root, ref, extent_op,
>
> btrfs_lookup_extent_info takes the mutex on the head before it looks at it's
> ref_mod, so it should always be consistent. Maybe somebody else is messing
> with
> refs and not doing the same thing? If that's the case we should fix them by
> doing the same thing, this isn't a fix. Thanks,
>
> Josef
I understand from discussion on IRC that there may be updates to this
patch. But, FWIW, this patch addresses the multiple rsync problem I
was seeing.
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