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From: Benjamin Tissoires <bentiss@kernel.org>
Subject: [PATCH bpf-next v2 00/16] Introduce bpf_wq
Date: Sat, 20 Apr 2024 11:09:00 +0200
Message-Id: <20240420-bpf_wq-v2-0-6c986a5a741f@kernel.org>
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To: Alexei Starovoitov <ast@kernel.org>, 
 Daniel Borkmann <daniel@iogearbox.net>, Andrii Nakryiko <andrii@kernel.org>, 
 Martin KaFai Lau <martin.lau@linux.dev>, 
 Eduard Zingerman <eddyz87@gmail.com>, Song Liu <song@kernel.org>, 
 Yonghong Song <yonghong.song@linux.dev>, 
 John Fastabend <john.fastabend@gmail.com>, KP Singh <kpsingh@kernel.org>, 
 Stanislav Fomichev <sdf@google.com>, Hao Luo <haoluo@google.com>, 
 Jiri Olsa <jolsa@kernel.org>, Mykola Lysenko <mykolal@fb.com>, 
 Shuah Khan <shuah@kernel.org>
Cc: bpf@vger.kernel.org, linux-kernel@vger.kernel.org, 
 linux-kselftest@vger.kernel.org, Benjamin Tissoires <bentiss@kernel.org>

This is a followup of sleepable bpf_timer[0].

When discussing sleepable bpf_timer, it was thought that we should give
a try to bpf_wq, as the 2 APIs are similar but distinct enough to
justify a new one.

So here it is.

I tried to keep as much as possible common code in kernel/bpf/helpers.c
but I couldn't get away with code duplication in kernel/bpf/verifier.c.

This series introduces a basic bpf_wq support:
- creation is supported
- assignment is supported
- running a simple bpf_wq is also supported.

We will probably need to extend the API further with:
- a full delayed_work API (can be piggy backed on top with a correct
  flag)
- bpf_wq_cancel() <- apparently not, this is shooting ourself in the
  foot
- bpf_wq_cancel_sync() (for sleepable programs)
- documentation

---

For reference, the use cases I have in mind:

---

Basically, I need to be able to defer a HID-BPF program for the
following reasons (from the aforementioned patch):
1. defer an event:
   Sometimes we receive an out of proximity event, but the device can not
   be trusted enough, and we need to ensure that we won't receive another
   one in the following n milliseconds. So we need to wait those n
   milliseconds, and eventually re-inject that event in the stack.

2. inject new events in reaction to one given event:
   We might want to transform one given event into several. This is the
   case for macro keys where a single key press is supposed to send
   a sequence of key presses. But this could also be used to patch a
   faulty behavior, if a device forgets to send a release event.

3. communicate with the device in reaction to one event:
   We might want to communicate back to the device after a given event.
   For example a device might send us an event saying that it came back
   from sleeping state and needs to be re-initialized.

Currently we can achieve that by keeping a userspace program around,
raise a bpf event, and let that userspace program inject the events and
commands.
However, we are just keeping that program alive as a daemon for just
scheduling commands. There is no logic in it, so it doesn't really justify
an actual userspace wakeup. So a kernel workqueue seems simpler to handle.

bpf_timers are currently running in a soft IRQ context, this patch
series implements a sleppable context for them.

Cheers,
Benjamin

To: Alexei Starovoitov <ast@kernel.org>
To: Daniel Borkmann <daniel@iogearbox.net>
To: Andrii Nakryiko <andrii@kernel.org>
To: Martin KaFai Lau <martin.lau@linux.dev>
To: Eduard Zingerman <eddyz87@gmail.com>
To: Song Liu <song@kernel.org>
To: Yonghong Song <yonghong.song@linux.dev>
To: John Fastabend <john.fastabend@gmail.com>
To: KP Singh <kpsingh@kernel.org>
To: Stanislav Fomichev <sdf@google.com>
To: Hao Luo <haoluo@google.com>
To: Jiri Olsa <jolsa@kernel.org>
To: Mykola Lysenko <mykolal@fb.com>
To: Shuah Khan <shuah@kernel.org>
Cc:  <bpf@vger.kernel.org>
Cc:  <linux-kernel@vger.kernel.org>
Cc:  <linux-kselftest@vger.kernel.org>
Signed-off-by: Benjamin Tissoires <bentiss@kernel.org>

[0] https://lore.kernel.org/all/20240408-hid-bpf-sleepable-v6-0-0499ddd91b94@kernel.org/

---
Changes in v2:
- took previous review into account
- mainly dropped BPF_F_WQ_SLEEPABLE
- Link to v1: https://lore.kernel.org/r/20240416-bpf_wq-v1-0-c9e66092f842@kernel.org

---
Benjamin Tissoires (16):
      bpf: make timer data struct more generic
      bpf: replace bpf_timer_init with a generic helper
      bpf: replace bpf_timer_set_callback with a generic helper
      bpf: replace bpf_timer_cancel_and_free with a generic helper
      bpf: add support for bpf_wq user type
      tools: sync include/uapi/linux/bpf.h
      bpf: verifier: bail out if the argument is not a map
      bpf: add support for KF_ARG_PTR_TO_WORKQUEUE
      bpf: allow struct bpf_wq to be embedded in arraymaps and hashmaps
      selftests/bpf: add bpf_wq tests
      bpf: wq: add bpf_wq_init
      selftests/bpf: wq: add bpf_wq_init() checks
      bpf: wq: add bpf_wq_set_callback_impl
      selftests/bpf: add checks for bpf_wq_set_callback()
      bpf: add bpf_wq_start
      selftests/bpf: wq: add bpf_wq_start() checks

 include/linux/bpf.h                                |  13 +-
 include/linux/bpf_verifier.h                       |   1 +
 include/uapi/linux/bpf.h                           |   4 +
 kernel/bpf/arraymap.c                              |  18 +-
 kernel/bpf/btf.c                                   |  17 +
 kernel/bpf/hashtab.c                               |  55 +++-
 kernel/bpf/helpers.c                               | 348 ++++++++++++++++-----
 kernel/bpf/syscall.c                               |  15 +-
 kernel/bpf/verifier.c                              | 154 ++++++++-
 tools/include/uapi/linux/bpf.h                     |   4 +
 tools/testing/selftests/bpf/bpf_experimental.h     |   7 +
 .../selftests/bpf/bpf_testmod/bpf_testmod.c        |   5 +
 .../selftests/bpf/bpf_testmod/bpf_testmod_kfunc.h  |   1 +
 tools/testing/selftests/bpf/prog_tests/wq.c        |  41 +++
 tools/testing/selftests/bpf/progs/wq.c             | 186 +++++++++++
 tools/testing/selftests/bpf/progs/wq_failures.c    | 144 +++++++++
 16 files changed, 910 insertions(+), 103 deletions(-)
---
base-commit: ffa6b26b4d8a0520b78636ca9373ab842cb3b1a8
change-id: 20240411-bpf_wq-fe24e8d24f5e

Best regards,
-- 
Benjamin Tissoires <bentiss@kernel.org>