On Tue, May 23, 2023 at 06:58:01AM +0000, aloktiagi wrote:
> Introduce a mechanism to replace a file linked in the epoll interface with a new
> file.
>
> eventpoll_replace() finds all instances of the file to be replaced and replaces
> them with the new file and the interested events.
>
> Signed-off-by: aloktiagi <aloktiagi@xxxxxxxxx>
> ---
> Changes in v6:
> - incorporate latest changes that get rid of the global epmutex lock.
>
> Changes in v5:
> - address review comments and move the call to replace old file in each
> subsystem (epoll, io_uring, etc.) outside the fdtable helpers like
> replace_fd().
>
> Changes in v4:
> - address review comment to remove the redundant eventpoll_replace() function.
> - removed an extra empty line introduced in include/linux/file.h
>
> Changes in v3:
> - address review comment and iterate over the file table while holding the
> spin_lock(&files->file_lock).
> - address review comment and call filp_close() outside the
> spin_lock(&files->file_lock).
> ---
> fs/eventpoll.c | 76 +++++++++++++++++++++++++++++++++++++++
> include/linux/eventpoll.h | 8 +++++
> 2 files changed, 84 insertions(+)
>
> diff --git a/fs/eventpoll.c b/fs/eventpoll.c
> index 980483455cc0..9c7bffa8401b 100644
> --- a/fs/eventpoll.c
> +++ b/fs/eventpoll.c
> @@ -973,6 +973,82 @@ void eventpoll_release_file(struct file *file)
> spin_unlock(&file->f_lock);
> }
>
> +static int ep_insert(struct eventpoll *ep, const struct epoll_event *event,
> + struct file *tfile, int fd, int full_check);
> +
> +/*
> + * This is called from eventpoll_replace() to replace a linked file in the epoll
> + * interface with a new file received from another process. This is useful in
> + * cases where a process is trying to install a new file for an existing one
> + * that is linked in the epoll interface
> + */
> +int eventpoll_replace_file(struct file *toreplace, struct file *file, int tfd)
> +{
> + struct file *to_remove = toreplace;
> + struct epoll_event event;
> + struct hlist_node *next;
> + struct eventpoll *ep;
> + struct epitem *epi;
> + int error = 0;
> + bool dispose;
> + int fd;
> +
> + if (!file_can_poll(file))
> + return 0;
> +
> + spin_lock(&toreplace->f_lock);
> + if (unlikely(!toreplace->f_ep)) {
> + spin_unlock(&toreplace->f_lock);
> + return 0;
> + }
> + hlist_for_each_entry_safe(epi, next, toreplace->f_ep, fllink) {
> + ep = epi->ep;
> + mutex_lock(&ep->mtx);
Afaict, you're under a spinlock and you're acquiring a mutex. The
spinlock can't sleep (on non-rt kernels at least) but the mutex can.
> + fd = epi->ffd.fd;
> + if (fd != tfd) {
> + mutex_unlock(&ep->mtx);
> + continue;
> + }
> + event = epi->event;
> + error = ep_insert(ep, &event, file, fd, 1);
> + mutex_unlock(&ep->mtx);
> + if (error != 0) {
> + break;
> + }
nit: we don't do { } around single lines.
