Re: [PATCH 2/3] liveupdate: keep sessions retrievable after release failures

[Pasha Tatashin]

Hi Leo,

Sorry for dup, accidentally switched to HTML mode in previous reply,
and therefore it was rejected from the mailing lists.

On Tue, Mar 24, 2026 at 2:03 PM Leo Timmins <leotimmins1974@xxxxxxxxx> wrote:
>
> When automatic finish-on-release fails for an incoming session,
> luo_session_release() cannot report that error back through close(). The
> VFS ignores ->release() return values during __fput().

Exactly. Since userspace can't detect a close() failure without
parsing dmesg, we shouldn't design around it. The API gives explicit
ioctl(LIVEUPDATE_SESSION_FINISH) that user should use before closing
the session, and if needed repeate finish again.

If userspace closes the session fd before finishing, we have to treat
it as a userspace bug. While it does mean the resource leaks until the
next live update or reboot, trying to work around this by allowing
session retrieval after a close() doesn't make sense. There is no
clean way for userspace to know the session is even still there;
perhaps blindly firing ioctl(LIVEUPDATE_SESSION_RETRIEVE_FD) would
allow querying that.

> Returning with session->retrieved still set leaves the session on the
> incoming list but impossible to retrieve again after the file descriptor
> is gone. Clear the retrieved flag so userspace can reopen the session and
> retry finishing it later.
>
> Fixes: 16cec0d26521 ("liveupdate: luo_session: add ioctls for file preservation")

It changes functionality, not really sure that Fixes applies.

> Signed-off-by: Leo Timmins <leotimmins1974@xxxxxxxxx>
> ---
>  kernel/liveupdate/luo_session.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/liveupdate/luo_session.c b/kernel/liveupdate/luo_session.c
> index 25ae704d7787..7016d96ee960 100644
> --- a/kernel/liveupdate/luo_session.c
> +++ b/kernel/liveupdate/luo_session.c
> @@ -210,9 +210,11 @@ static int luo_session_release(struct inode *inodep, struct file *filep)
>                 int err = luo_session_finish_one(session);
>
>                 if (err) {
> +                       scoped_guard(mutex, &session->mutex)
> +                               session->retrieved = false;
>                         pr_warn("Unable to finish session [%s] on release\n",
>                                 session->name);
> -                       return err;
> +                       return 0;

close() do not return failure to userspace, but is there a
disadvantage in propagating this up?

Thanks,
Pasha

>                 }
>                 sh = &luo_session_global.incoming;
>         } else {
> --
> 2.53.0