Re: [PATCH v7 2/2] btrfs: Handle delalloc error correctly to avoid ordered extent hang

[Filipe Manana <fdmanana@kernel.org>]

On Wed, Mar 8, 2017 at 2:25 AM, Qu Wenruo <quwenruo@cn.fujitsu.com> wrote:
> [BUG]
> If run_delalloc_range() returns error and there is already some ordered
> extents created, btrfs will be hanged with the following backtrace:
>
> Call Trace:
>  __schedule+0x2d4/0xae0
>  schedule+0x3d/0x90
>  btrfs_start_ordered_extent+0x160/0x200 [btrfs]
>  ? wake_atomic_t_function+0x60/0x60
>  btrfs_run_ordered_extent_work+0x25/0x40 [btrfs]
>  btrfs_scrubparity_helper+0x1c1/0x620 [btrfs]
>  btrfs_flush_delalloc_helper+0xe/0x10 [btrfs]
>  process_one_work+0x2af/0x720
>  ? process_one_work+0x22b/0x720
>  worker_thread+0x4b/0x4f0
>  kthread+0x10f/0x150
>  ? process_one_work+0x720/0x720
>  ? kthread_create_on_node+0x40/0x40
>  ret_from_fork+0x2e/0x40
>
> [CAUSE]
>
> |<------------------ delalloc range --------------------------->|
> | OE 1 | OE 2 | ... | OE n |
> |<>|                       |<---------- cleanup range --------->|
>  ||
>  \_=> First page handled by end_extent_writepage() in __extent_writepage()
>
> The problem is caused by error handler of run_delalloc_range(), which
> doesn't handle any created ordered extents, leaving them waiting on
> btrfs_finish_ordered_io() to finish.
>
> However after run_delalloc_range() returns error, __extent_writepage()
> won't submit bio, so btrfs_writepage_end_io_hook() won't be triggered
> except the first page, and btrfs_finish_ordered_io() won't be triggered
> for created ordered extents either.
>
> So OE 2~n will hang forever, and if OE 1 is larger than one page, it
> will also hang.
>
> [FIX]
> Introduce btrfs_cleanup_ordered_extents() function to cleanup created
> ordered extents and finish them manually.
>
> The function is based on existing
> btrfs_endio_direct_write_update_ordered() function, and modify it to
> act just like btrfs_writepage_endio_hook() but handles specified range
> other than one page.
>
> After fix, delalloc error will be handled like:
>
> |<------------------ delalloc range --------------------------->|
> | OE 1 | OE 2 | ... | OE n |
> |<>|<--------  ----------->|<------ old error handler --------->|
>  ||          ||
>  ||          \_=> Cleaned up by cleanup_ordered_extents()
>  \_=> First page handled by end_extent_writepage() in __extent_writepage()
>
> Signed-off-by: Qu Wenruo <quwenruo@cn.fujitsu.com>

Reviewed-by: Filipe Manana <fdmanana@suse.com>

thanks

> Signed-off-by: Filipe Manana <fdmanana@suse.com>
> ---
> v2:
>   Add BTRFS_ORDERED_SKIP_METADATA flag to avoid double reducing
>   outstanding extents, which is already done by
>   extent_clear_unlock_delalloc() with EXTENT_DO_ACCOUNT control bit
> v3:
>   Skip first page to avoid underflow ordered->bytes_left.
>   Fix range passed in cow_file_range() which doesn't cover the whole
>   extent.
>   Expend extent_clear_unlock_delalloc() range to allow them to handle
>   metadata release.
> v4:
>   Don't use extra bit to skip metadata freeing for ordered extent,
>   but only handle btrfs_reloc_clone_csums() error just before processing
>   next extent.
>   This makes error handle much easier for run_delalloc_nocow().
> v5:
>   Variant gramma and comment fixes suggested by Filipe Manana
>   Enhanced commit message to focus on the generic error handler bug,
>   pointed out by Filipe Manana
>   Adding missing wq/func user in __endio_write_update_ordered(), pointed
>   out by Filipe Manana.
>   Enhanced commit message with ascii art to explain the bug more easily.
>   Fix a bug which can leads to corrupted extent allocation, exposed by
>   Filipe Manana.
> v6:
>   Split the metadata underflow fix to another patch.
>   Use better comment and btrfs_cleanup_ordered_extent() implementation
>   from Filipe Manana.
> v7:
>   Add back const prefix
> ---
>  fs/btrfs/inode.c | 63 ++++++++++++++++++++++++++++++++++++++++++--------------
>  1 file changed, 48 insertions(+), 15 deletions(-)
>
> diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
> index fe588bf30d02..d3bc68bbe0e7 100644
> --- a/fs/btrfs/inode.c
> +++ b/fs/btrfs/inode.c
> @@ -115,6 +115,31 @@ static struct extent_map *create_io_em(struct inode *inode, u64 start, u64 len,
>                                        u64 ram_bytes, int compress_type,
>                                        int type);
>
> +static void __endio_write_update_ordered(struct inode *inode,
> +                                        const u64 offset, const u64 bytes,
> +                                        const bool uptodate);
> +
> +/*
> + * Cleanup all submitted ordered extents in specified range to handle errors
> + * from the fill_dellaloc() callback.
> + *
> + * NOTE: caller must ensure that when an error happens, it can not call
> + * extent_clear_unlock_delalloc() to clear both the bits EXTENT_DO_ACCOUNTING
> + * and EXTENT_DELALLOC simultaneously, because that causes the reserved metadata
> + * to be released, which we want to happen only when finishing the ordered
> + * extent (btrfs_finish_ordered_io()). Also note that the caller of the
> + * fill_delalloc() callback already does proper cleanup for the first page of
> + * the range, that is, it invokes the callback writepage_end_io_hook() for the
> + * range of the first page.
> + */
> +static inline void btrfs_cleanup_ordered_extents(struct inode *inode,
> +                                                const u64 offset,
> +                                                const u64 bytes)
> +{
> +       return __endio_write_update_ordered(inode, offset + PAGE_SIZE,
> +                                           bytes - PAGE_SIZE, false);
> +}
> +
>  static int btrfs_dirty_inode(struct inode *inode);
>
>  #ifdef CONFIG_BTRFS_FS_RUN_SANITY_TESTS
> @@ -1536,6 +1561,8 @@ static int run_delalloc_range(struct inode *inode, struct page *locked_page,
>                 ret = cow_file_range_async(inode, locked_page, start, end,
>                                            page_started, nr_written);
>         }
> +       if (ret)
> +               btrfs_cleanup_ordered_extents(inode, start, end - start + 1);
>         return ret;
>  }
>
> @@ -8142,17 +8169,26 @@ static void btrfs_endio_direct_read(struct bio *bio)
>         bio_put(bio);
>  }
>
> -static void btrfs_endio_direct_write_update_ordered(struct inode *inode,
> -                                                   const u64 offset,
> -                                                   const u64 bytes,
> -                                                   const int uptodate)
> +static void __endio_write_update_ordered(struct inode *inode,
> +                                        const u64 offset, const u64 bytes,
> +                                        const bool uptodate)
>  {
>         struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
>         struct btrfs_ordered_extent *ordered = NULL;
> +       struct btrfs_workqueue *wq;
> +       btrfs_work_func_t func;
>         u64 ordered_offset = offset;
>         u64 ordered_bytes = bytes;
>         int ret;
>
> +       if (btrfs_is_free_space_inode(BTRFS_I(inode))) {
> +               wq = fs_info->endio_freespace_worker;
> +               func = btrfs_freespace_write_helper;
> +       } else {
> +               wq = fs_info->endio_write_workers;
> +               func = btrfs_endio_write_helper;
> +       }
> +
>  again:
>         ret = btrfs_dec_test_first_ordered_pending(inode, &ordered,
>                                                    &ordered_offset,
> @@ -8161,9 +8197,8 @@ static void btrfs_endio_direct_write_update_ordered(struct inode *inode,
>         if (!ret)
>                 goto out_test;
>
> -       btrfs_init_work(&ordered->work, btrfs_endio_write_helper,
> -                       finish_ordered_fn, NULL, NULL);
> -       btrfs_queue_work(fs_info->endio_write_workers, &ordered->work);
> +       btrfs_init_work(&ordered->work, func, finish_ordered_fn, NULL, NULL);
> +       btrfs_queue_work(wq, &ordered->work);
>  out_test:
>         /*
>          * our bio might span multiple ordered extents.  If we haven't
> @@ -8181,10 +8216,8 @@ static void btrfs_endio_direct_write(struct bio *bio)
>         struct btrfs_dio_private *dip = bio->bi_private;
>         struct bio *dio_bio = dip->dio_bio;
>
> -       btrfs_endio_direct_write_update_ordered(dip->inode,
> -                                               dip->logical_offset,
> -                                               dip->bytes,
> -                                               !bio->bi_error);
> +       __endio_write_update_ordered(dip->inode, dip->logical_offset,
> +                                    dip->bytes, !bio->bi_error);
>
>         kfree(dip);
>
> @@ -8545,10 +8578,10 @@ static void btrfs_submit_direct(struct bio *dio_bio, struct inode *inode,
>                 io_bio = NULL;
>         } else {
>                 if (write)
> -                       btrfs_endio_direct_write_update_ordered(inode,
> +                       __endio_write_update_ordered(inode,
>                                                 file_offset,
>                                                 dio_bio->bi_iter.bi_size,
> -                                               0);
> +                                               false);
>                 else
>                         unlock_extent(&BTRFS_I(inode)->io_tree, file_offset,
>                               file_offset + dio_bio->bi_iter.bi_size - 1);
> @@ -8683,11 +8716,11 @@ static ssize_t btrfs_direct_IO(struct kiocb *iocb, struct iov_iter *iter)
>                          */
>                         if (dio_data.unsubmitted_oe_range_start <
>                             dio_data.unsubmitted_oe_range_end)
> -                               btrfs_endio_direct_write_update_ordered(inode,
> +                               __endio_write_update_ordered(inode,
>                                         dio_data.unsubmitted_oe_range_start,
>                                         dio_data.unsubmitted_oe_range_end -
>                                         dio_data.unsubmitted_oe_range_start,
> -                                       0);
> +                                       false);
>                 } else if (ret >= 0 && (size_t)ret < count)
>                         btrfs_delalloc_release_space(inode, offset,
>                                                      count - (size_t)ret);
> --
> 2.12.0
>
>
>