On 5/17/17 4:52 PM, Noah Massey wrote:
> On Wed, May 17, 2017 at 4:34 PM, Nikolay Borisov <nbori...@suse.com> wrote:
>>
>>
>> On 17.05.2017 21:57, Noah Massey wrote:
>>> On Wed, May 17, 2017 at 11:07 AM, Nikolay Borisov <nbori...@suse.com> wrote:
>>>> Currently the struct space_info creation code is intermixed in the
>>>> udpate_space_info function. There are well-defined points at which the we
>>>
>>> ^^^ update_space_info
>>>
>>>> actually want to create brand-new space_info structs (e.g. during mount of
>>>> the filesystem as well as sometimes when adding/initialising new chunks).
>>>> In
>>>> such cases udpate_space_info is called with 0 as the bytes parameter. All
>>>> of
>>>> this makes for spaghetti code.
>>>>
>>>> Fix it by factoring out the creation code in a separate create_space_info
>>>> structure. This also allows to simplify the internals. Furthermore it will
>>>> make the update_space_info function not fail, allowing to remove error
>>>> handling in callers. This will come in a follow up patch.
>>>>
>>>> This bears no functional changes
>>>>
>>>> Signed-off-by: Nikolay Borisov <nbori...@suse.com>
>>>> Reviewed-by: Jeff Mahoney <je...@suse.com>
>>>> ---
>>>> fs/btrfs/extent-tree.c | 127
>>>> ++++++++++++++++++++++++-------------------------
>>>> 1 file changed, 62 insertions(+), 65 deletions(-)
>>>>
>>>> Change since v1:
>>>>
>>>> Incorporated Jeff Mahoney's feedback and added his reviewed-by
>>>>
>>>> diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
>>>> index be5477676cc8..28848e45b018 100644
>>>> --- a/fs/btrfs/extent-tree.c
>>>> +++ b/fs/btrfs/extent-tree.c
>>>> @@ -3914,15 +3914,58 @@ static const char *alloc_name(u64 flags)
>>>> };
>>>> }
>>>>
>>>> +static int create_space_info(struct btrfs_fs_info *info, u64 flags,
>>>> + struct btrfs_space_info **new) {
>>>> +
>>>> + struct btrfs_space_info *space_info;
>>>> + int i;
>>>> + int ret;
>>>> +
>>>> + space_info = kzalloc(sizeof(*space_info), GFP_NOFS);
>>>> + if (!space_info)
>>>> + return -ENOMEM;
>>>> +
>>>> + ret = percpu_counter_init(&space_info->total_bytes_pinned, 0,
>>>> GFP_KERNEL);
>>>> + if (ret) {
>>>> + kfree(space_info);
>>>> + return ret;
>>>> + }
>>>> +
>>>> + for (i = 0; i < BTRFS_NR_RAID_TYPES; i++)
>>>> + INIT_LIST_HEAD(&space_info->block_groups[i]);
>>>> + init_rwsem(&space_info->groups_sem);
>>>> + spin_lock_init(&space_info->lock);
>>>> + space_info->flags = flags & BTRFS_BLOCK_GROUP_TYPE_MASK;
>>>> + space_info->force_alloc = CHUNK_ALLOC_NO_FORCE;
>>>> + init_waitqueue_head(&space_info->wait);
>>>> + INIT_LIST_HEAD(&space_info->ro_bgs);
>>>> + INIT_LIST_HEAD(&space_info->tickets);
>>>> + INIT_LIST_HEAD(&space_info->priority_tickets);
>>>> +
>>>> + ret = kobject_init_and_add(&space_info->kobj, &space_info_ktype,
>>>> + info->space_info_kobj, "%s",
>>>> + alloc_name(space_info->flags));
>>>> + if (ret) {
>>>> + percpu_counter_destroy(&space_info->total_bytes_pinned);
>>>> + kfree(space_info);
>>>> + return ret;
>>>> + }
>>>> +
>>>> + *new = space_info;
>>>> + list_add_rcu(&space_info->list, &info->space_info);
>>>> + if (flags & BTRFS_BLOCK_GROUP_DATA)
>>>> + info->data_sinfo = space_info;
>>>> +
>>>> + return ret;
>>>> +}
>>>> +
>>>> static int update_space_info(struct btrfs_fs_info *info, u64 flags,
>>>> u64 total_bytes, u64 bytes_used,
>>>> u64 bytes_readonly,
>>>> struct btrfs_space_info **space_info)
>>>> {
>>>> struct btrfs_space_info *found;
>>>> - int i;
>>>> int factor;
>>>> - int ret;
>>>>
>>>> if (flags & (BTRFS_BLOCK_GROUP_DUP | BTRFS_BLOCK_GROUP_RAID1 |
>>>> BTRFS_BLOCK_GROUP_RAID10))
>>>> @@ -3946,53 +3989,6 @@ static int update_space_info(struct btrfs_fs_info
>>>> *info, u64 flags,
>>>> *space_info = found;
>>>> return 0;
>>>> }
>>>> - found = kzalloc(sizeof(*found), GFP_NOFS);
>>>> - if (!found)
>>>> - return -ENOMEM;
>>>> -
>>>> - ret = percpu_counter_init(&found->total_bytes_pinned, 0,
>>>> GFP_KERNEL);
>>>> - if (ret) {
>>>> - kfree(found);
>>>> - return ret;
>>>> - }
>>>> -
>>>> - for (i = 0; i < BTRFS_NR_RAID_TYPES; i++)
>>>> - INIT_LIST_HEAD(&found->block_groups[i]);
>>>> - init_rwsem(&found->groups_sem);
>>>> - spin_lock_init(&found->lock);
>>>> - found->flags = flags & BTRFS_BLOCK_GROUP_TYPE_MASK;
>>>> - found->total_bytes = total_bytes;
>>>> - found->disk_total = total_bytes * factor;
>>>> - found->bytes_used = bytes_used;
>>>> - found->disk_used = bytes_used * factor;
>>>> - found->bytes_pinned = 0;
>>>> - found->bytes_reserved = 0;
>>>> - found->bytes_readonly = bytes_readonly;
>>>> - found->bytes_may_use = 0;
>>>> - found->full = 0;
>>>> - found->max_extent_size = 0;
>>>> - found->force_alloc = CHUNK_ALLOC_NO_FORCE;
>>>> - found->chunk_alloc = 0;
>>>> - found->flush = 0;
>>>> - init_waitqueue_head(&found->wait);
>>>> - INIT_LIST_HEAD(&found->ro_bgs);
>>>> - INIT_LIST_HEAD(&found->tickets);
>>>> - INIT_LIST_HEAD(&found->priority_tickets);
>>>> -
>>>> - ret = kobject_init_and_add(&found->kobj, &space_info_ktype,
>>>> - info->space_info_kobj, "%s",
>>>> - alloc_name(found->flags));
>>>> - if (ret) {
>>>> - kfree(found);
>>>> - return ret;
>>>> - }
>>>> -
>>>> - *space_info = found;
>>>> - list_add_rcu(&found->list, &info->space_info);
>>>> - if (flags & BTRFS_BLOCK_GROUP_DATA)
>>>> - info->data_sinfo = found;
>>>> -
>>>> - return ret;
>>>> }
>>>>
>>>> static void set_avail_alloc_bits(struct btrfs_fs_info *fs_info, u64 flags)
>>>> @@ -4495,10 +4491,9 @@ static int do_chunk_alloc(struct btrfs_trans_handle
>>>> *trans,
>>>>
>>>> space_info = __find_space_info(fs_info, flags);
>>>> if (!space_info) {
>>>> - ret = update_space_info(fs_info, flags, 0, 0, 0,
>>>> &space_info);
>>>> + ret = create_space_info(fs_info, flags, &space_info);
>>>> BUG_ON(ret); /* -ENOMEM */
>>>> }
>>>> - BUG_ON(!space_info); /* Logic error */
>>>
>>> Isn't removing this BUG_ON a functional change?
>>> I understand that it shouldn't happen in the current incarnation of
>>> create_space_info, but that was true before the patch as well
>>
>> No, because this bug_on would have triggere only if !space_info, and
>> this condition would have, in turn, triggered the if statement, which
>> has a BUG_ON(ret). E.g. in case ret is 0 then space_info will definitely
>> be set. Hence BUG_ON(!space_info) is redundant.
>>
>
> But the BUG_ON(ret) value is independent of BUG_ON(!space_info)
> The BUG_ON(!space_info) seems to have been there to catch a potential
> logic error if update_space_info is modified / regressed to return 0
> and still not set space_info pointer, so removing the BUG_ON seems to
> be a change separate from the switch to create_space_info.The BUG_ON(!space_info) is older than the call to update_space_info(). It should've been removed when we started creating the space info there. -Jeff > I'm not saying it can't be removed: the current code looks good, and I > agree the BUG_ON won't trigger. It looks like the current incarnation > of create_space_info will always set space_info or return an error, > but so did the previous call to update_space_info, so I was not sure > it should be dropped as part of the switch. > > Is the thinking that since we are switching the called method and in > the new current code the BUG_ON won't trigger, there will be no > behavior change by removing it so we can drop it in the update? -- Jeff Mahoney SUSE Labs
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