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Message-ID: <b49529b9-3f1c-be5f-f95a-dadceae057ec@oracle.com>
Date: Fri, 13 Aug 2021 18:30:02 +0800
From: Anand Jain <anand.jain@...cle.com>
To: Qu Wenruo <quwenruo.btrfs@....com>, linux-kernel@...r.kernel.org,
stable@...r.kernel.org
Cc: linux-btrfs@...r.kernel.org, Qu Wenruo <wqu@...e.com>,
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 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.
-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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