linux-kernel - Re: [PATCH v2] f2fs: fix deadlock in i_xattr_sem and inode page lock and fix the original issue

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Date:   Wed, 28 Jun 2023 16:36:13 +0800
From:   Chao Yu <chao@...nel.org>
To:     Jaegeuk Kim <jaegeuk@...nel.org>
Cc:     linux-kernel@...r.kernel.org,
        linux-f2fs-devel@...ts.sourceforge.net, stable@...r.kernel.org
Subject: Re: [PATCH v2] f2fs: fix deadlock in i_xattr_sem and inode page lock
 and fix the original issue

On 2023/6/28 16:08, Jaegeuk Kim wrote:
> Thread #1:
> 
> [122554.641906][   T92]  f2fs_getxattr+0xd4/0x5fc
>      -> waiting for f2fs_down_read(&F2FS_I(inode)->i_xattr_sem);
> 
> [122554.641927][   T92]  __f2fs_get_acl+0x50/0x284
> [122554.641948][   T92]  f2fs_init_acl+0x84/0x54c
> [122554.641969][   T92]  f2fs_init_inode_metadata+0x460/0x5f0
> [122554.641990][   T92]  f2fs_add_inline_entry+0x11c/0x350
>      -> Locked dir->inode_page by f2fs_get_node_page()
> 
> [122554.642009][   T92]  f2fs_do_add_link+0x100/0x1e4
> [122554.642025][   T92]  f2fs_create+0xf4/0x22c
> [122554.642047][   T92]  vfs_create+0x130/0x1f4
> 
> Thread #2:
> 
> [123996.386358][   T92]  __get_node_page+0x8c/0x504
>      -> waiting for dir->inode_page lock
> 
> [123996.386383][   T92]  read_all_xattrs+0x11c/0x1f4
> [123996.386405][   T92]  __f2fs_setxattr+0xcc/0x528
> [123996.386424][   T92]  f2fs_setxattr+0x158/0x1f4
>      -> f2fs_down_write(&F2FS_I(inode)->i_xattr_sem);
> 
> [123996.386443][   T92]  __f2fs_set_acl+0x328/0x430
> [123996.386618][   T92]  f2fs_set_acl+0x38/0x50
> [123996.386642][   T92]  posix_acl_chmod+0xc8/0x1c8
> [123996.386669][   T92]  f2fs_setattr+0x5e0/0x6bc
> [123996.386689][   T92]  notify_change+0x4d8/0x580
> [123996.386717][   T92]  chmod_common+0xd8/0x184
> [123996.386748][   T92]  do_fchmodat+0x60/0x124
> [123996.386766][   T92]  __arm64_sys_fchmodat+0x28/0x3c

Back to the race condition, my question is why we can chmod on inode before
it has been created?

Thanks,

> 
> Fixes: 27161f13e3c3 "f2fs: avoid race in between read xattr & write xattr"
> Cc: <stable@...r.kernel.org>
> Signed-off-by: Jaegeuk Kim <jaegeuk@...nel.org>
> ---
>   fs/f2fs/dir.c   | 9 ++++++++-
>   fs/f2fs/xattr.c | 6 ++++--
>   2 files changed, 12 insertions(+), 3 deletions(-)
> 
> diff --git a/fs/f2fs/dir.c b/fs/f2fs/dir.c
> index 887e55988450..d635c58cf5a3 100644
> --- a/fs/f2fs/dir.c
> +++ b/fs/f2fs/dir.c
> @@ -775,8 +775,15 @@ int f2fs_add_dentry(struct inode *dir, const struct f2fs_filename *fname,
>   {
>   	int err = -EAGAIN;
>   
> -	if (f2fs_has_inline_dentry(dir))
> +	if (f2fs_has_inline_dentry(dir)) {
> +		/*
> +		 * Should get i_xattr_sem to keep the lock order:
> +		 * i_xattr_sem -> inode_page lock used by f2fs_setxattr.
> +		 */
> +		f2fs_down_read(&F2FS_I(dir)->i_xattr_sem);
>   		err = f2fs_add_inline_entry(dir, fname, inode, ino, mode);
> +		f2fs_up_read(&F2FS_I(dir)->i_xattr_sem);
> +	}
>   	if (err == -EAGAIN)
>   		err = f2fs_add_regular_entry(dir, fname, inode, ino, mode);
>   
> diff --git a/fs/f2fs/xattr.c b/fs/f2fs/xattr.c
> index 213805d3592c..476b186b90a6 100644
> --- a/fs/f2fs/xattr.c
> +++ b/fs/f2fs/xattr.c
> @@ -528,10 +528,12 @@ int f2fs_getxattr(struct inode *inode, int index, const char *name,
>   	if (len > F2FS_NAME_LEN)
>   		return -ERANGE;
>   
> -	f2fs_down_read(&F2FS_I(inode)->i_xattr_sem);
> +	if (!ipage)
> +		f2fs_down_read(&F2FS_I(inode)->i_xattr_sem);
>   	error = lookup_all_xattrs(inode, ipage, index, len, name,
>   				&entry, &base_addr, &base_size, &is_inline);
> -	f2fs_up_read(&F2FS_I(inode)->i_xattr_sem);
> +	if (!ipage)
> +		f2fs_up_read(&F2FS_I(inode)->i_xattr_sem);
>   	if (error)
>   		return error;
>