[PATCH 0/5 v2] seccomp: add the synchronous mode for seccomp_unotify

[Andrei Vagin <avagin@gmail.com>]

seccomp_unotify allows more privileged processes does actions on behalf
of less privileged processes.

In many cases, the workflow is fully synchronous. It means a target
process triggers a system call and passes controls to a supervisor
process that handles the system call and returns controls back to the
target process. In this context, "synchronous" means that only one
process is running and another one is waiting.

The new WF_CURRENT_CPU flag advises the scheduler to move the wakee to
the current CPU. For such synchronous workflows, it makes context
switches a few times faster.

Right now, each interaction takes 12µs. With this patch, it takes about
3µs.

v2: clean up the first patch and add the test.

Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Peter Oskolkov <posk@google.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Tycho Andersen <tycho@tycho.pizza>
Cc: Will Drewry <wad@chromium.org>
Cc: Vincent Guittot <vincent.guittot@linaro.org>

Andrei Vagin (4):
  seccomp: don't use semaphore and wait_queue together
  sched: add a few helpers to wake up tasks on the current cpu
  seccomp: add the synchronous mode for seccomp_unotify
  selftest/seccomp: add a new test for the sync mode of
    seccomp_user_notify

Peter Oskolkov (1):
  sched: add WF_CURRENT_CPU and externise ttwu

 include/linux/completion.h                    |  1 +
 include/linux/swait.h                         |  1 +
 include/linux/wait.h                          |  3 +
 include/uapi/linux/seccomp.h                  |  4 +
 kernel/sched/completion.c                     | 12 +++
 kernel/sched/core.c                           |  5 +-
 kernel/sched/fair.c                           |  4 +
 kernel/sched/sched.h                          | 13 +--
 kernel/sched/swait.c                          | 11 +++
 kernel/sched/wait.c                           |  5 ++
 kernel/seccomp.c                              | 72 +++++++++++++++--
 tools/testing/selftests/seccomp/seccomp_bpf.c | 80 +++++++++++++++++++
 12 files changed, 196 insertions(+), 15 deletions(-)

-- 
2.37.2