linux-kernel - Re: [f2fs-dev] [PATCH 1/2] f2fs: fix wrong extent

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Message-ID: <228203f5-d3bf-46fb-b990-3de2eb2ff3e8@kernel.org>
Date: Thu, 11 Sep 2025 16:19:06 +0800
From: Chao Yu <chao@...nel.org>
To: wangzijie <wangzijie1@...or.com>, jaegeuk@...nel.org
Cc: chao@...nel.org, bintian.wang@...or.com, feng.han@...or.com,
 linux-kernel@...r.kernel.org, linux-f2fs-devel@...ts.sourceforge.net
Subject: Re: [f2fs-dev] [PATCH 1/2] f2fs: fix wrong extent_info data for
 precache extents

On 9/10/25 21:58, wangzijie wrote:
> When the data layout is like this:
> dnode1:                     dnode2:
> [0]      A                  [0]    NEW_ADDR
> [1]      A+1                [1]    0x0
> ...                         ....
> [1016]   A+1016
> [1017]   B (B!=A+1017)      [1017] 0x0
> 
> We can build this kind of layout by following steps(with i_extra_isize:36):
> ./f2fs_io write 1 0 1881 rand dsync testfile
> ./f2fs_io write 1 1881 1 rand buffered testfile
> ./f2fs_io fallocate 0 7708672 4096 testfile
> 
> And when we map first data block in dnode2, we will get wrong extent_info data:
> map->m_len = 1
> ofs = start_pgofs - map->m_lblk = 1882 - 1881 = 1
> 
> ei.fofs = start_pgofs = 1882
> ei.len = map->m_len - ofs = 1 - 1 = 0
> 
> Fix it by skipping updating this kind of extent info.
> 
> Signed-off-by: wangzijie <wangzijie1@...or.com>
> ---
>  fs/f2fs/data.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
> index 7961e0ddf..b8bb71852 100644
> --- a/fs/f2fs/data.c
> +++ b/fs/f2fs/data.c
> @@ -1649,6 +1649,9 @@ int f2fs_map_blocks(struct inode *inode, struct f2fs_map_blocks *map, int flag)
>  
>  		switch (flag) {
>  		case F2FS_GET_BLOCK_PRECACHE:
> +			if (__is_valid_data_blkaddr(map->m_pblk) &&
> +				start_pgofs - map->m_lblk == map->m_len)
> +				map->m_flags &= ~F2FS_MAP_MAPPED;

It looks we missed to reset value for map variable in f2fs_precache_extents(),
what do you think of this?

---
 fs/f2fs/file.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
index 1aae4361d0a8..2b14151d4130 100644
--- a/fs/f2fs/file.c
+++ b/fs/f2fs/file.c
@@ -3599,7 +3599,7 @@ static int f2fs_ioc_io_prio(struct file *filp, unsigned long arg)
 int f2fs_precache_extents(struct inode *inode)
 {
 	struct f2fs_inode_info *fi = F2FS_I(inode);
-	struct f2fs_map_blocks map;
+	struct f2fs_map_blocks map = { 0 };
 	pgoff_t m_next_extent;
 	loff_t end;
 	int err;
@@ -3617,6 +3617,8 @@ int f2fs_precache_extents(struct inode *inode)

 	while (map.m_lblk < end) {
 		map.m_len = end - map.m_lblk;
+		map.m_pblk = 0;
+		map.m_flags = 0;

 		f2fs_down_write(&fi->i_gc_rwsem[WRITE]);
 		err = f2fs_map_blocks(inode, &map, F2FS_GET_BLOCK_PRECACHE);
-- 
2.49.0

Thanks,

>  			goto sync_out;
>  		case F2FS_GET_BLOCK_BMAP:
>  			map->m_pblk = 0;