Re: [PATCH] f2fs: avoid race between zero_range and background GC

From: Jaegeuk Kim
Date: Fri Jul 27 2018 - 06:29:22 EST


On 07/26, Chao Yu wrote:
> Thread A Background GC
> - f2fs_zero_range
> - truncate_pagecache_range
> - gc_data_segment
> - get_read_data_page
> - move_data_page
> - set_page_dirty
> - set_cold_data
> - f2fs_do_zero_range
> - dn->data_blkaddr = NEW_ADDR;
> - f2fs_set_data_blkaddr
>
> Actually, we don't need to set dirty & checked flag on the page, since
> all valid data in the page should be zeroed by zero_range().

But, it doesn't matter too much, right?

> Use i_gc_rwsem[WRITE] to avoid such race condition.

Hope to avoid abusing i_gc_rwsem[] tho.

>
> Signed-off-by: Chao Yu <yuchao0@xxxxxxxxxx>
> ---
> fs/f2fs/file.c | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
> index 267ec3794e1e..7bd2412a8c37 100644
> --- a/fs/f2fs/file.c
> +++ b/fs/f2fs/file.c
> @@ -1309,6 +1309,7 @@ static int f2fs_zero_range(struct inode *inode, loff_t offset, loff_t len,
> if (ret)
> return ret;
>
> + down_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
> down_write(&F2FS_I(inode)->i_mmap_sem);
> ret = filemap_write_and_wait_range(mapping, offset, offset + len - 1);
> if (ret)
> @@ -1389,6 +1390,7 @@ static int f2fs_zero_range(struct inode *inode, loff_t offset, loff_t len,
> }
> out_sem:
> up_write(&F2FS_I(inode)->i_mmap_sem);
> + up_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
>
> return ret;
> }
> --
> 2.18.0.rc1