Re: [PATCH] ext4: Fix the issue of missing lock in ext4_page_mkwrite

[Baokun Li <libaokun1@huawei.com>]

Hi Penglei,

On 2025/3/30 15:55, Penglei Jiang wrote:
> In ext4_page_mkwrite, it calls ext4_convert_inline_data, but it does
> not use inode_lock to hold i_rwsem.
>
> Fixes: 7b4cc9787fe35 ("ext4: evict inline data when writing to memory map")
> Reported-by: syzbot+d14b2bea87fe2aaffa3b@syzkaller.appspotmail.com
> Closes: https://lore.kernel.org/all/67e57c6c.050a0220.2f068f.0037.GAE@google.com
> Signed-off-by: Penglei Jiang <superman.xpt@gmail.com>
> ---
>   fs/ext4/inode.c | 3 +++
>   1 file changed, 3 insertions(+)
>
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index bcb96caf77c0..4e726c86377a 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -6203,6 +6203,8 @@ vm_fault_t ext4_page_mkwrite(struct vm_fault *vmf)
>   	sb_start_pagefault(inode->i_sb);
>   	file_update_time(vma->vm_file);
>   
> +	inode_lock(inode);
> +
>   	filemap_invalidate_lock_shared(mapping);
>   
>   	err = ext4_convert_inline_data(inode);
We cannot directly add inode_lock here, otherwise it may cause ABBA
deadlock. The inline data conversion here does lack inode_lock, but
there is no good way to fix it now. For details, please see:

https://lore.kernel.org/all/d704ce55-321a-9c1d-1f8b-3360a0fdf978@huawei.com/
> @@ -6308,6 +6310,7 @@ vm_fault_t ext4_page_mkwrite(struct vm_fault *vmf)
>   	ret = vmf_fs_error(err);
>   out:
>   	filemap_invalidate_unlock_shared(mapping);
> +	inode_unlock(inode);
>   	sb_end_pagefault(inode->i_sb);
>   	return ret;
>   out_error: