linux-kernel - Re: [PATCH 2/2] fuse: Relax backing file validation to compare backing inodes

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Message-ID: <CAOQ4uxhB-L93cj3RbqLy=618ZsFr0B1d3DH0zV+gD-A5BngQrw@mail.gmail.com>
Date: Fri, 16 Jan 2026 16:07:27 +0100
From: Amir Goldstein <amir73il@...il.com>
To: Chunsheng Luo <luochunsheng@...c.edu>
Cc: miklos@...redi.hu, linux-fsdevel@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] fuse: Relax backing file validation to compare
 backing inodes

On Fri, Jan 16, 2026 at 3:28 PM Chunsheng Luo <luochunsheng@...c.edu> wrote:
>
> To simplify crash recovery and reduce performance impact, backing_ids
> are not persisted across daemon restarts. However, when the daemon
> restarts and another process open the same FUSE file and assigning it
> the same backing file (with the same inode) will also cause the
> fuse_inode_uncached_io_start() function to fail due to a mismatch in
> the fb pointer.
>
> So Relax the validation in fuse_inode_uncached_io_start() to compare
> backing inodes instead of fuse_backing pointers.
>
> Signed-off-by: Chunsheng Luo <luochunsheng@...c.edu>
Reviewed-by: Amir Goldstein <amir73il@...il.com>

> ---
>  fs/fuse/iomode.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/fs/fuse/iomode.c b/fs/fuse/iomode.c
> index 3728933188f3..ca7619958b0d 100644
> --- a/fs/fuse/iomode.c
> +++ b/fs/fuse/iomode.c
> @@ -90,7 +90,7 @@ int fuse_inode_uncached_io_start(struct fuse_inode *fi, struct fuse_backing *fb)
>         spin_lock(&fi->lock);
>         /* deny conflicting backing files on same fuse inode */
>         oldfb = fuse_inode_backing(fi);
> -       if (fb && oldfb && oldfb != fb) {
> +       if (fb && oldfb && file_inode(oldfb->file) != file_inode(fb->file)) {
>                 err = -EBUSY;
>                 goto unlock;
>         }
> --
> 2.43.0
>