[PATCH] f2fs: add READ_ONCE() for i_blocks in f2fs_update_inode()

[PATCH] f2fs: add READ_ONCE() for i_blocks in f2fs_update_inode()

[Cen Zhang]

f2fs_update_inode() reads inode->i_blocks without holding i_lock to
serialize it to the on-disk inode, while concurrent truncate or
allocation paths may modify i_blocks under i_lock.  Since blkcnt_t is
u64, this risks torn reads on 32-bit architectures.

Following the approach in ext4_inode_blocks_set(), add READ_ONCE() to prevent
potential compiler-induced tearing.

Signed-off-by: Cen Zhang <zzzccc427@gmail.com>
---
 fs/f2fs/inode.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/f2fs/inode.c b/fs/f2fs/inode.c
index 078874db918c..73b913dbe02a 100644
--- a/fs/f2fs/inode.c
+++ b/fs/f2fs/inode.c
@@ -694,7 +694,7 @@ void f2fs_update_inode(struct inode *inode, struct folio *node_folio)
 	ri->i_uid = cpu_to_le32(i_uid_read(inode));
 	ri->i_gid = cpu_to_le32(i_gid_read(inode));
 	ri->i_links = cpu_to_le32(inode->i_nlink);
-	ri->i_blocks = cpu_to_le64(SECTOR_TO_BLOCK(inode->i_blocks) + 1);
+	ri->i_blocks = cpu_to_le64(SECTOR_TO_BLOCK(READ_ONCE(inode->i_blocks)) + 1);
 
 	if (!f2fs_is_atomic_file(inode) ||
 			is_inode_flag_set(inode, FI_ATOMIC_COMMITTED))
-- 
2.34.1

Re: [PATCH] f2fs: add READ_ONCE() for i_blocks in f2fs_update_inode()

[Chao Yu]

On 2026/3/17 19:42, Cen Zhang wrote:
> f2fs_update_inode() reads inode->i_blocks without holding i_lock to
> serialize it to the on-disk inode, while concurrent truncate or
> allocation paths may modify i_blocks under i_lock.  Since blkcnt_t is
> u64, this risks torn reads on 32-bit architectures.
> 
> Following the approach in ext4_inode_blocks_set(), add READ_ONCE() to prevent
> potential compiler-induced tearing.
> 

Need a Fixes line and Cc stable@kernel.org?

Otherwise, it looks good to me.

Thanks,

> Signed-off-by: Cen Zhang <zzzccc427@gmail.com>
> ---
>   fs/f2fs/inode.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/f2fs/inode.c b/fs/f2fs/inode.c
> index 078874db918c..73b913dbe02a 100644
> --- a/fs/f2fs/inode.c
> +++ b/fs/f2fs/inode.c
> @@ -694,7 +694,7 @@ void f2fs_update_inode(struct inode *inode, struct folio *node_folio)
>   	ri->i_uid = cpu_to_le32(i_uid_read(inode));
>   	ri->i_gid = cpu_to_le32(i_gid_read(inode));
>   	ri->i_links = cpu_to_le32(inode->i_nlink);
> -	ri->i_blocks = cpu_to_le64(SECTOR_TO_BLOCK(inode->i_blocks) + 1);
> +	ri->i_blocks = cpu_to_le64(SECTOR_TO_BLOCK(READ_ONCE(inode->i_blocks)) + 1);
>   
>   	if (!f2fs_is_atomic_file(inode) ||
>   			is_inode_flag_set(inode, FI_ATOMIC_COMMITTED))

Re: [PATCH] f2fs: add READ_ONCE() for i_blocks in f2fs_update_inode()

[Cen Zhang]

Hi Chao,

Thank you for the review.

On 2026/3/18 13:56, Chao Yu wrote:
> Need a Fixes line and Cc stable@kernel.org?

Good point, added both in v2:

  Fixes: 19f99cee206c ("f2fs: add core inode operations")
  Cc: stable@vger.kernel.org

> Otherwise, it looks good to me.

Thanks!

Best regards,
Cen