linux-kernel - [PATCH 0/3] riscv: ftrace: Fixup ftrace detour code

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Message-Id: <20220916103817.9490-1-guoren@kernel.org>
Date:   Fri, 16 Sep 2022 06:38:14 -0400
From:   guoren@...nel.org
To:     arnd@...db.de, guoren@...nel.org, palmer@...osinc.com,
        rostedt@...dmis.org, andy.chiu@...ive.com, greentime.hu@...ive.com,
        zong.li@...ive.com, jrtc27@...c27.com, mingo@...hat.com
Cc:     linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-riscv@...ts.infradead.org, Guo Ren <guoren@...ux.alibaba.com>
Subject: [PATCH 0/3] riscv: ftrace: Fixup ftrace detour code

From: Guo Ren <guoren@...ux.alibaba.com>

The previous ftrace detour implementation fc76b8b8011 ("riscv: Using
PATCHABLE_FUNCTION_ENTRY instead of MCOUNT") contain three problems. The
most horrible bug is preemption panic which found by Andy [1]. I think we
could disable preemption for ftrace first, and Andy could continue the
ftrace preemption work.

@Andy, as Steven said, improving stop_machine mechinism also could prevent
preemption problem, but it would reduce the speed of ftrace_modify. How
do you think about the stop_machine solution, would you give out the
patch for this?

[1]: https://lpc.events/event/16/contributions/1171/

Andy Chiu (1):
  riscv: ftrace: Fixup panic by disabling preemption

Guo Ren (2):
  riscv: ftrace: Remove wasted nops for !RISCV_ISA_C
  riscv: ftrace: Reduce the detour code size to half

 arch/riscv/Kconfig              |  2 +-
 arch/riscv/Makefile             |  6 ++-
 arch/riscv/include/asm/ftrace.h | 46 ++++++++++++++++++-----
 arch/riscv/kernel/ftrace.c      | 65 ++++++++++-----------------------
 arch/riscv/kernel/mcount-dyn.S  | 43 +++++++++-------------
 5 files changed, 78 insertions(+), 84 deletions(-)

-- 
2.36.1