Merge tag 'pidfd-fixes-v5.1-rc3' of gitolite.kernel.org:pub/scm/linux/kernel/git/brauner/linux

Pull pidfd fix from Christian Brauner:
"This should be an uncontroversial fix for pidfd_send_signal() by Jann
to better align it's behavior with other signal sending functions:

In one of the early versions of the patchset it was suggested to not
unconditionally error out when a signal with SI_USER is sent to a
non-current task (cf. [1]).

Instead, pidfd_send_signal() currently silently changes this to a
regular kill signal. While this is technically fine, the semantics are
weird since the kernel just silently converts a user's request behind
their back and also no other signal sending function allows to do
this. It gets more hairy when we introduce sending signals to a
specific thread soon.

So let's align pidfd_send_signal() with all the other signal sending
functions and error out when SI_USER signals are sent to a non-current
task"

* tag 'pidfd-fixes-v5.1-rc3' of gitolite.kernel.org:pub/scm/linux/kernel/git/brauner/linux:
signal: don't silently convert SI_USER signals to non-current pidfd