Message-ID: <6f45f8c6-03df-b2e0-cfda-85fd0b41212a@suse.com>
Date:   Fri, 13 Aug 2021 18:39:04 +0800
From:   Qu Wenruo <wqu@...e.com>
To:     Anand Jain <anand.jain@...cle.com>,
        Qu Wenruo <quwenruo.btrfs@....com>,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     linux-btrfs@...r.kernel.org, Josef Bacik <josef@...icpanda.com>,
        David Sterba <dsterba@...e.com>
Subject: Re: [PATCH 4/7] btrfs: qgroup: try to flush qgroup space when we get
 -EDQUOT



On 2021/8/13 下午6:30, Anand Jain wrote:
> 
> 
> On 13/08/2021 18:26, Qu Wenruo wrote:
>>
>>
>> On 2021/8/13 下午5:55, Anand Jain wrote:
>>> From: Qu Wenruo <wqu@...e.com>
>>>
>>> commit c53e9653605dbf708f5be02902de51831be4b009 upstream
>>
>> This lacks certain upstream fixes for it:
>>
>> f9baa501b4fd6962257853d46ddffbc21f27e344 btrfs: fix deadlock when
>> cloning inline extents and using qgroups
>>
>> 4d14c5cde5c268a2bc26addecf09489cb953ef64 btrfs: don't flush from
>> btrfs_delayed_inode_reserve_metadata
>>
>> 6f23277a49e68f8a9355385c846939ad0b1261e7 btrfs: qgroup: don't commit
>> transaction when we already hold the handle
>>
>> All these fixes are to ensure we don't try to flush in context where we
>> shouldn't.
>>
>> Without them, it can hit various deadlock.
>>
> 
> Qu,
> 
>     Thanks for taking a look. I will send it in v2.

I guess you only need to add the missing fixes?

Thanks,
Qu
> 
> -Anand
> 
> 
>> Thanks,
>> Qu
>>>
>>> [PROBLEM]
>>> There are known problem related to how btrfs handles qgroup reserved
>>> space.  One of the most obvious case is the the test case btrfs/153,
>>> which do fallocate, then write into the preallocated range.
>>>
>>>    btrfs/153 1s ... - output mismatch (see 
>>> xfstests-dev/results//btrfs/153.out.bad)
>>>        --- tests/btrfs/153.out     2019-10-22 15:18:14.068965341 +0800
>>>        +++ xfstests-dev/results//btrfs/153.out.bad      2020-07-01 
>>> 20:24:40.730000089 +0800
>>>        @@ -1,2 +1,5 @@
>>>         QA output created by 153
>>>        +pwrite: Disk quota exceeded
>>>        +/mnt/scratch/testfile2: Disk quota exceeded
>>>        +/mnt/scratch/testfile2: Disk quota exceeded
>>>         Silence is golden
>>>        ...
>>>        (Run 'diff -u xfstests-dev/tests/btrfs/153.out 
>>> xfstests-dev/results//btrfs/153.out.bad'  to see the entire diff)
>>>
>>> [CAUSE]
>>> Since commit c6887cd11149 ("Btrfs: don't do nocow check unless we 
>>> have to"),
>>> we always reserve space no matter if it's COW or not.
>>>
>>> Such behavior change is mostly for performance, and reverting it is not
>>> a good idea anyway.
>>>
>>> For preallcoated extent, we reserve qgroup data space for it already,
>>> and since we also reserve data space for qgroup at buffered write time,
>>> it needs twice the space for us to write into preallocated space.
>>>
>>> This leads to the -EDQUOT in buffered write routine.
>>>
>>> And we can't follow the same solution, unlike data/meta space check,
>>> qgroup reserved space is shared between data/metadata.
>>> The EDQUOT can happen at the metadata reservation, so doing NODATACOW
>>> check after qgroup reservation failure is not a solution.
>>>
>>> [FIX]
>>> To solve the problem, we don't return -EDQUOT directly, but every time
>>> we got a -EDQUOT, we try to flush qgroup space:
>>>
>>> - Flush all inodes of the root
>>>    NODATACOW writes will free the qgroup reserved at 
>>> run_dealloc_range().
>>>    However we don't have the infrastructure to only flush NODATACOW
>>>    inodes, here we flush all inodes anyway.
>>>
>>> - Wait for ordered extents
>>>    This would convert the preallocated metadata space into per-trans
>>>    metadata, which can be freed in later transaction commit.
>>>
>>> - Commit transaction
>>>    This will free all per-trans metadata space.
>>>
>>> Also we don't want to trigger flush multiple times, so here we introduce
>>> a per-root wait list and a new root status, to ensure only one thread
>>> starts the flushing.
>>>
>>> Fixes: c6887cd11149 ("Btrfs: don't do nocow check unless we have to")
>>> Reviewed-by: Josef Bacik <josef@...icpanda.com>
>>> Signed-off-by: Qu Wenruo <wqu@...e.com>
>>> Reviewed-by: David Sterba <dsterba@...e.com>
>>> Signed-off-by: David Sterba <dsterba@...e.com>
>>> Signed-off-by: Anand Jain <anand.jain@...cle.com>
>>> ---
>>>   fs/btrfs/ctree.h   |   3 ++
>>>   fs/btrfs/disk-io.c |   1 +
>>>   fs/btrfs/qgroup.c  | 100 +++++++++++++++++++++++++++++++++++++++++----
>>>   3 files changed, 96 insertions(+), 8 deletions(-)
>>>
>>> diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
>>> index 7960359dbc70..5448dc62e915 100644
>>> --- a/fs/btrfs/ctree.h
>>> +++ b/fs/btrfs/ctree.h
>>> @@ -945,6 +945,8 @@ enum {
>>>       BTRFS_ROOT_DEAD_TREE,
>>>       /* The root has a log tree. Used only for subvolume roots. */
>>>       BTRFS_ROOT_HAS_LOG_TREE,
>>> +    /* Qgroup flushing is in progress */
>>> +    BTRFS_ROOT_QGROUP_FLUSHING,
>>>   };
>>>
>>>   /*
>>> @@ -1097,6 +1099,7 @@ struct btrfs_root {
>>>       spinlock_t qgroup_meta_rsv_lock;
>>>       u64 qgroup_meta_rsv_pertrans;
>>>       u64 qgroup_meta_rsv_prealloc;
>>> +    wait_queue_head_t qgroup_flush_wait;
>>>
>>>       /* Number of active swapfiles */
>>>       atomic_t nr_swapfiles;
>>> diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
>>> index e6aa94a583e9..e3bcab38a166 100644
>>> --- a/fs/btrfs/disk-io.c
>>> +++ b/fs/btrfs/disk-io.c
>>> @@ -1154,6 +1154,7 @@ static void __setup_root(struct btrfs_root 
>>> *root, struct btrfs_fs_info *fs_info,
>>>       mutex_init(&root->log_mutex);
>>>       mutex_init(&root->ordered_extent_mutex);
>>>       mutex_init(&root->delalloc_mutex);
>>> +    init_waitqueue_head(&root->qgroup_flush_wait);
>>>       init_waitqueue_head(&root->log_writer_wait);
>>>       init_waitqueue_head(&root->log_commit_wait[0]);
>>>       init_waitqueue_head(&root->log_commit_wait[1]);
>>> diff --git a/fs/btrfs/qgroup.c b/fs/btrfs/qgroup.c
>>> index 50c45b4fcfd4..b312ac645e08 100644
>>> --- a/fs/btrfs/qgroup.c
>>> +++ b/fs/btrfs/qgroup.c
>>> @@ -3479,17 +3479,58 @@ static int qgroup_unreserve_range(struct 
>>> btrfs_inode *inode,
>>>   }
>>>
>>>   /*
>>> - * Reserve qgroup space for range [start, start + len).
>>> + * Try to free some space for qgroup.
>>>    *
>>> - * This function will either reserve space from related qgroups or 
>>> doing
>>> - * nothing if the range is already reserved.
>>> + * For qgroup, there are only 3 ways to free qgroup space:
>>> + * - Flush nodatacow write
>>> + *   Any nodatacow write will free its reserved data space at 
>>> run_delalloc_range().
>>> + *   In theory, we should only flush nodatacow inodes, but it's not yet
>>> + *   possible, so we need to flush the whole root.
>>>    *
>>> - * Return 0 for successful reserve
>>> - * Return <0 for error (including -EQUOT)
>>> + * - Wait for ordered extents
>>> + *   When ordered extents are finished, their reserved metadata is 
>>> finally
>>> + *   converted to per_trans status, which can be freed by later commit
>>> + *   transaction.
>>>    *
>>> - * NOTE: this function may sleep for memory allocation.
>>> + * - Commit transaction
>>> + *   This would free the meta_per_trans space.
>>> + *   In theory this shouldn't provide much space, but any more 
>>> qgroup space
>>> + *   is needed.
>>>    */
>>> -int btrfs_qgroup_reserve_data(struct btrfs_inode *inode,
>>> +static int try_flush_qgroup(struct btrfs_root *root)
>>> +{
>>> +    struct btrfs_trans_handle *trans;
>>> +    int ret;
>>> +
>>> +    /*
>>> +     * We don't want to run flush again and again, so if there is a 
>>> running
>>> +     * one, we won't try to start a new flush, but exit directly.
>>> +     */
>>> +    if (test_and_set_bit(BTRFS_ROOT_QGROUP_FLUSHING, &root->state)) {
>>> +        wait_event(root->qgroup_flush_wait,
>>> +            !test_bit(BTRFS_ROOT_QGROUP_FLUSHING, &root->state));
>>> +        return 0;
>>> +    }
>>> +
>>> +    ret = btrfs_start_delalloc_snapshot(root);
>>> +    if (ret < 0)
>>> +        goto out;
>>> +    btrfs_wait_ordered_extents(root, U64_MAX, 0, (u64)-1);
>>> +
>>> +    trans = btrfs_join_transaction(root);
>>> +    if (IS_ERR(trans)) {
>>> +        ret = PTR_ERR(trans);
>>> +        goto out;
>>> +    }
>>> +
>>> +    ret = btrfs_commit_transaction(trans);
>>> +out:
>>> +    clear_bit(BTRFS_ROOT_QGROUP_FLUSHING, &root->state);
>>> +    wake_up(&root->qgroup_flush_wait);
>>> +    return ret;
>>> +}
>>> +
>>> +static int qgroup_reserve_data(struct btrfs_inode *inode,
>>>               struct extent_changeset **reserved_ret, u64 start,
>>>               u64 len)
>>>   {
>>> @@ -3542,6 +3583,34 @@ int btrfs_qgroup_reserve_data(struct 
>>> btrfs_inode *inode,
>>>       return ret;
>>>   }
>>>
>>> +/*
>>> + * Reserve qgroup space for range [start, start + len).
>>> + *
>>> + * This function will either reserve space from related qgroups or 
>>> do nothing
>>> + * if the range is already reserved.
>>> + *
>>> + * Return 0 for successful reservation
>>> + * Return <0 for error (including -EQUOT)
>>> + *
>>> + * NOTE: This function may sleep for memory allocation, dirty page 
>>> flushing and
>>> + *     commit transaction. So caller should not hold any dirty page 
>>> locked.
>>> + */
>>> +int btrfs_qgroup_reserve_data(struct btrfs_inode *inode,
>>> +            struct extent_changeset **reserved_ret, u64 start,
>>> +            u64 len)
>>> +{
>>> +    int ret;
>>> +
>>> +    ret = qgroup_reserve_data(inode, reserved_ret, start, len);
>>> +    if (ret <= 0 && ret != -EDQUOT)
>>> +        return ret;
>>> +
>>> +    ret = try_flush_qgroup(inode->root);
>>> +    if (ret < 0)
>>> +        return ret;
>>> +    return qgroup_reserve_data(inode, reserved_ret, start, len);
>>> +}
>>> +
>>>   /* Free ranges specified by @reserved, normally in error path */
>>>   static int qgroup_free_reserved_data(struct btrfs_inode *inode,
>>>               struct extent_changeset *reserved, u64 start, u64 len)
>>> @@ -3712,7 +3781,7 @@ static int sub_root_meta_rsv(struct btrfs_root 
>>> *root, int num_bytes,
>>>       return num_bytes;
>>>   }
>>>
>>> -int __btrfs_qgroup_reserve_meta(struct btrfs_root *root, int num_bytes,
>>> +static int qgroup_reserve_meta(struct btrfs_root *root, int num_bytes,
>>>                   enum btrfs_qgroup_rsv_type type, bool enforce)
>>>   {
>>>       struct btrfs_fs_info *fs_info = root->fs_info;
>>> @@ -3739,6 +3808,21 @@ int __btrfs_qgroup_reserve_meta(struct 
>>> btrfs_root *root, int num_bytes,
>>>       return ret;
>>>   }
>>>
>>> +int __btrfs_qgroup_reserve_meta(struct btrfs_root *root, int num_bytes,
>>> +                enum btrfs_qgroup_rsv_type type, bool enforce)
>>> +{
>>> +    int ret;
>>> +
>>> +    ret = qgroup_reserve_meta(root, num_bytes, type, enforce);
>>> +    if (ret <= 0 && ret != -EDQUOT)
>>> +        return ret;
>>> +
>>> +    ret = try_flush_qgroup(root);
>>> +    if (ret < 0)
>>> +        return ret;
>>> +    return qgroup_reserve_meta(root, num_bytes, type, enforce);
>>> +}
>>> +
>>>   void btrfs_qgroup_free_meta_all_pertrans(struct btrfs_root *root)
>>>   {
>>>       struct btrfs_fs_info *fs_info = root->fs_info;
>>>
> 

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