Re: [PATCH 3/3] overlayfs: Initialize OVL_UPPERDATA in ovl_lookup()

From: Amir Goldstein <amir73il@gmail.com>
To: Vivek Goyal <vgoyal@redhat.com>
Cc: Miklos Szeredi <miklos@szeredi.hu>,
	yangerkun <yangerkun@huawei.com>,
	overlayfs <linux-unionfs@vger.kernel.org>
Subject: Re: [PATCH 3/3] overlayfs: Initialize OVL_UPPERDATA in ovl_lookup()
Date: Sat, 30 May 2020 14:02:43 +0300	[thread overview]
Message-ID: <CAOQ4uxiv5LqLouM1AJran0Y_EHk6D1uq5368CoCEqxOhA4_waA@mail.gmail.com> (raw)
In-Reply-To: <20200529212952.214175-4-vgoyal@redhat.com>

On Sat, May 30, 2020 at 12:30 AM Vivek Goyal <vgoyal@redhat.com> wrote:
>
> Currently ovl_get_inode() initializes OVL_UPPERDATA flag and for that it
> has to call ovl_check_metacopy_xattr() and check if metacopy xattr is
> present or not.
>
> yangerkun reported sometimes underlying filesystem might return -EIO
> and in that case error handling path does not cleanup properly leading
> to various warnings.
>
> Run generic/461 with ext4 upper/lower layer sometimes may trigger the
> bug as below(linux 4.19):
>
> [  551.001349] overlayfs: failed to get metacopy (-5)
> [  551.003464] overlayfs: failed to get inode (-5)
> [  551.004243] overlayfs: cleanup of 'd44/fd51' failed (-5)
> [  551.004941] overlayfs: failed to get origin (-5)
> [  551.005199] ------------[ cut here ]------------
> [  551.006697] WARNING: CPU: 3 PID: 24674 at fs/inode.c:1528 iput+0x33b/0x400
> ...
> [  551.027219] Call Trace:
> [  551.027623]  ovl_create_object+0x13f/0x170
> [  551.028268]  ovl_create+0x27/0x30
> [  551.028799]  path_openat+0x1a35/0x1ea0
> [  551.029377]  do_filp_open+0xad/0x160
> [  551.029944]  ? vfs_writev+0xe9/0x170
> [  551.030499]  ? page_counter_try_charge+0x77/0x120
> [  551.031245]  ? __alloc_fd+0x160/0x2a0
> [  551.031832]  ? do_sys_open+0x189/0x340
> [  551.032417]  ? get_unused_fd_flags+0x34/0x40
> [  551.033081]  do_sys_open+0x189/0x340
> [  551.033632]  __x64_sys_creat+0x24/0x30
> [  551.034219]  do_syscall_64+0xd5/0x430
> [  551.034800]  entry_SYSCALL_64_after_hwframe+0x44/0xa9
>
> One solution is to improve error handling and call iget_failed() if error
> is encountered. Amir thinks that this path is little intricate and there
> is not real need to check and initialize OVL_UPPERDATA in ovl_get_inode().
> Instead caller of ovl_get_inode() can initialize this state. And this
> will avoid double checking of metacopy xattr lookup in ovl_lookup()
> and ovl_get_inode().
>
> OVL_UPPERDATA is inode flag. So I was little concerned that initializing
> it outside ovl_get_inode() might have some races. But this is one way
> transition. That is once a file has been fully copied up, it can't go
> back to metacopy file again. And that seems to help avoid races. So
> as of now I can't see any races w.r.t OVL_UPPERDATA being set wrongly. So
> move settingof OVL_UPPERDATA inside the callers of ovl_get_inode().
> ovl_obtain_alias() already does it. So only two callers now left
> are ovl_lookup() and ovl_instantiate().
>
> Reported-by: yangerkun <yangerkun@huawei.com>
> Suggested-by: Amir Goldstein <amir73il@gmail.com>
> Signed-off-by: Vivek Goyal <vgoyal@redhat.com>

Reviewed-by: Amir Goldstein <amir73il@gmail.com>

> ---
>  fs/overlayfs/dir.c   |  2 ++
>  fs/overlayfs/inode.c | 11 +----------
>  fs/overlayfs/namei.c |  2 ++
>  3 files changed, 5 insertions(+), 10 deletions(-)
>
> diff --git a/fs/overlayfs/dir.c b/fs/overlayfs/dir.c
> index 279009dee366..a7cac2ce0fad 100644
> --- a/fs/overlayfs/dir.c
> +++ b/fs/overlayfs/dir.c
> @@ -262,6 +262,8 @@ static int ovl_instantiate(struct dentry *dentry, struct inode *inode,
>                 inode = ovl_get_inode(dentry->d_sb, &oip);
>                 if (IS_ERR(inode))
>                         return PTR_ERR(inode);
> +               if (inode == oip.newinode)
> +                       ovl_set_flag(OVL_UPPERDATA, inode);
>         } else {
>                 WARN_ON(ovl_inode_real(inode) != d_inode(newdentry));
>                 dput(newdentry);
> diff --git a/fs/overlayfs/inode.c b/fs/overlayfs/inode.c
> index 981f11ec51bc..f2aaf00821c0 100644
> --- a/fs/overlayfs/inode.c
> +++ b/fs/overlayfs/inode.c
> @@ -957,7 +957,7 @@ struct inode *ovl_get_inode(struct super_block *sb,
>         bool bylower = ovl_hash_bylower(sb, upperdentry, lowerdentry,
>                                         oip->index);
>         int fsid = bylower ? lowerpath->layer->fsid : 0;
> -       bool is_dir, metacopy = false;
> +       bool is_dir;
>         unsigned long ino = 0;
>         int err = oip->newinode ? -EEXIST : -ENOMEM;
>
> @@ -1018,15 +1018,6 @@ struct inode *ovl_get_inode(struct super_block *sb,
>         if (oip->index)
>                 ovl_set_flag(OVL_INDEX, inode);
>
> -       if (upperdentry) {
> -               err = ovl_check_metacopy_xattr(upperdentry);
> -               if (err < 0)
> -                       goto out_err;
> -               metacopy = err;
> -               if (!metacopy)
> -                       ovl_set_flag(OVL_UPPERDATA, inode);
> -       }
> -
>         OVL_I(inode)->redirect = oip->redirect;
>
>         if (bylower)
> diff --git a/fs/overlayfs/namei.c b/fs/overlayfs/namei.c
> index a1889a160708..36e2b88a2fd1 100644
> --- a/fs/overlayfs/namei.c
> +++ b/fs/overlayfs/namei.c
> @@ -1078,6 +1078,8 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
>                 err = PTR_ERR(inode);
>                 if (IS_ERR(inode))
>                         goto out_free_oe;
> +               if (upperdentry && !uppermetacopy)
> +                       ovl_set_flag(OVL_UPPERDATA, inode);
>         }
>
>         ovl_dentry_update_reval(dentry, upperdentry,
> --
> 2.25.4
>