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

[Naveen N. Rao]

Masami Hiramatsu wrote:
> Clear current_kprobe and enable preemption in kprobe
> even if pre_handler returns !0.
> 
> This simplifies function override using kprobes.
> 
> 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.
> 
> After removing the jprobe, Kprobes does not need to
> keep preempt disabled even if user handler returns !0
> anymore.
> 
> 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.
> 
> 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.
> 
> Note: for powerpc and x86, this removes all preempt_disable
> from kprobe_ftrace_handler because ftrace callbacks are
> called under preempt disabled.
> 
> Signed-off-by: Masami Hiramatsu <mhiramat at kernel.org>
> Cc: Vineet Gupta <vgupta at synopsys.com>
> Cc: Russell King <linux at armlinux.org.uk>
> Cc: Catalin Marinas <catalin.marinas at arm.com>
> Cc: Will Deacon <will.deacon at arm.com>
> Cc: Tony Luck <tony.luck at intel.com>
> Cc: Fenghua Yu <fenghua.yu at intel.com>
> Cc: Ralf Baechle <ralf at linux-mips.org>
> Cc: James Hogan <jhogan at kernel.org>
> Cc: Benjamin Herrenschmidt <benh at kernel.crashing.org>
> Cc: Paul Mackerras <paulus at samba.org>
> Cc: Michael Ellerman <mpe at ellerman.id.au>
> Cc: Martin Schwidefsky <schwidefsky at de.ibm.com>
> Cc: Heiko Carstens <heiko.carstens at de.ibm.com>
> Cc: Yoshinori Sato <ysato at users.sourceforge.jp>
> Cc: Rich Felker <dalias at libc.org>
> Cc: "David S. Miller" <davem at davemloft.net>
> Cc: "Naveen N. Rao" <naveen.n.rao at linux.vnet.ibm.com>
> Cc: Josef Bacik <jbacik at fb.com>
> Cc: Alexei Starovoitov <ast at kernel.org>
> Cc: x86 at kernel.org
> Cc: linux-snps-arc at lists.infradead.org
> Cc: linux-kernel at vger.kernel.org
> Cc: linux-arm-kernel at lists.infradead.org
> Cc: linux-ia64 at vger.kernel.org
> Cc: linux-mips at linux-mips.org
> Cc: linuxppc-dev at lists.ozlabs.org
> Cc: linux-s390 at vger.kernel.org
> Cc: linux-sh at vger.kernel.org
> Cc: sparclinux at 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 <naveen.n.rao at linux.vnet.ibm.com>

Thanks,
Naveen