Re: [RFC PATCH -tip v5 24/27] bpf: error-inject: kprobes: Clear current_kprobe and enable preempt in kprobe

Masami Hiramatsu wrote:

Clear current_kprobe and enable preemption in kprobe
even if pre_handler returns !0.
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This simplifies function override using kprobes.
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Jprobe used to require to keep the preemption disabled and
keep current_kprobe until it returned to original function
entry. For this reason kprobe_int3_handler() and similar
arch dependent kprobe handers checks pre_handler result
and exit without enabling preemption if the result is !0.
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After removing the jprobe, Kprobes does not need to
keep preempt disabled even if user handler returns !0
anymore.
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But since the function override handler in error-inject
and bpf is also returns !0 if it overrides a function,
to balancing the preempt count, it enables preemption
and reset current kprobe by itself.
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That is a bad design that is very buggy. This fixes
such unbalanced preempt-count and current_kprobes setting
in kprobes, bpf and error-inject.
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Note: for powerpc and x86, this removes all preempt_disable
from kprobe_ftrace_handler because ftrace callbacks are
called under preempt disabled.
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Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Vineet Gupta <redacted>
Cc: Russell King <linux@armlinux.org.uk>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <redacted>
Cc: Tony Luck <tony.luck@intel.com>
Cc: Fenghua Yu <redacted>
Cc: Ralf Baechle <redacted>
Cc: James Hogan <jhogan@kernel.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <redacted>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Martin Schwidefsky <redacted>
Cc: Heiko Carstens <redacted>
Cc: Yoshinori Sato <ysato@users.sourceforge.jp>
Cc: Rich Felker <dalias@libc.org>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: "Naveen N. Rao" <redacted>
Cc: Josef Bacik <redacted>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: x86@kernel.org
Cc: linux-snps-arc@lists.infradead.org
Cc: linux-kernel@vger.kernel.org
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-ia64@vger.kernel.org
Cc: linux-mips@linux-mips.org
Cc: linuxppc-dev@lists.ozlabs.org
Cc: linux-s390@vger.kernel.org
Cc: linux-sh@vger.kernel.org
Cc: sparclinux@vger.kernel.org
---
 Changes in v5:
  - Fix kprobe_ftrace_handler in arch/powerpc too.
---
 arch/arc/kernel/kprobes.c            |    5 +++--
 arch/arm/probes/kprobes/core.c       |   10 +++++-----
 arch/arm64/kernel/probes/kprobes.c   |   10 +++++-----
 arch/ia64/kernel/kprobes.c           |   13 ++++---------
 arch/mips/kernel/kprobes.c           |    4 ++--
 arch/powerpc/kernel/kprobes-ftrace.c |   15 ++++++---------
 arch/powerpc/kernel/kprobes.c        |    7 +++++--

For the powerpc bits:
Acked-by: Naveen N. Rao <redacted>

Thanks,
Naveen

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