Re: [PATCH] fuse: Fix deadlock on open(O_TRUNC)

[Peng Tao <bergwolf@gmail.com>]

On Fri, Aug 13, 2021 at 5:57 PM Xie Yongji <xieyongji@bytedance.com> wrote:
>
> The invalidate_inode_pages2() might be called with FUSE_NOWRITE
> set in fuse_finish_open(), which can lead to deadlock in
> fuse_launder_page().
>
> To fix it, this tries to delay calling invalidate_inode_pages2()
> until FUSE_NOWRITE is removed.
>
> Fixes: e4648309b85a ("fuse: truncate pending writes on O_TRUNC")
> Signed-off-by: Xie Yongji <xieyongji@bytedance.com>
> ---
>  fs/fuse/dir.c    |  2 +-
>  fs/fuse/file.c   | 19 +++++++++++++++----
>  fs/fuse/fuse_i.h |  2 +-
>  3 files changed, 17 insertions(+), 6 deletions(-)
>
> diff --git a/fs/fuse/dir.c b/fs/fuse/dir.c
> index eade6f965b2e..d919c3e89cb0 100644
> --- a/fs/fuse/dir.c
> +++ b/fs/fuse/dir.c
> @@ -548,7 +548,7 @@ static int fuse_create_open(struct inode *dir, struct dentry *entry,
>                 fuse_sync_release(fi, ff, flags);
>         } else {
>                 file->private_data = ff;
> -               fuse_finish_open(inode, file);
> +               fuse_finish_open(inode, file, false);
>         }
>         return err;
>
> diff --git a/fs/fuse/file.c b/fs/fuse/file.c
> index 97f860cfc195..035af9c88eaf 100644
> --- a/fs/fuse/file.c
> +++ b/fs/fuse/file.c
> @@ -193,12 +193,12 @@ static void fuse_link_write_file(struct file *file)
>         spin_unlock(&fi->lock);
>  }
>
> -void fuse_finish_open(struct inode *inode, struct file *file)
> +void fuse_finish_open(struct inode *inode, struct file *file, bool no_write)
>  {
>         struct fuse_file *ff = file->private_data;
>         struct fuse_conn *fc = get_fuse_conn(inode);
>
> -       if (!(ff->open_flags & FOPEN_KEEP_CACHE))
> +       if (!(ff->open_flags & FOPEN_KEEP_CACHE) && !no_write)
>                 invalidate_inode_pages2(inode->i_mapping);
It would break !FOPEN_KEEP_CACHE semantics, right? Fuse server asks
the kernel not to keep cache across open but kernel still keeps it?

Cheers,
Tao
-- 
Into Sth. Rich & Strange