On Tue, May 23, 2023 at 02:32:06PM +0200, Christian Brauner wrote:
> 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.
>
thank you. I'll address this in another way in the next patch series. Please
let me know of your opinion on how it can be achieved differently.
> > + 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.
will fix this in the next series.
