From: "Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com>
To: mhiramat@kernel.org, Peter Zijlstra <peterz@infradead.org>
Cc: ananth@linux.ibm.com, Christoph Hellwig <hch@lst.de>,
linux-kernel@vger.kernel.org, mingo@kernel.org,
rostedt@goodmis.org, x86@kernel.org
Subject: Re: [PATCH 1/2] kprobes: Remove kprobe::fault_handler
Date: Wed, 26 May 2021 16:20:25 +0530 [thread overview]
Message-ID: <1622025445.6q8nl3t4ap.naveen@linux.ibm.com> (raw)
In-Reply-To: <20210525073213.561116662@infradead.org>
Peter Zijlstra wrote:
> The reason for kprobe::fault_handler(), as given by their comment:
>
> * We come here because instructions in the pre/post
> * handler caused the page_fault, this could happen
> * if handler tries to access user space by
> * copy_from_user(), get_user() etc. Let the
> * user-specified handler try to fix it first.
>
> Is just plain bad. Those other handlers are ran from non-preemptible
> context and had better use _nofault() functions. Also, there is no
> upstream usage of this.
>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> Reviewed-by: Christoph Hellwig <hch@lst.de>
> ---
> Documentation/trace/kprobes.rst | 24 +++++-------------------
> arch/arc/kernel/kprobes.c | 10 ----------
> arch/arm/probes/kprobes/core.c | 9 ---------
> arch/arm64/kernel/probes/kprobes.c | 10 ----------
> arch/csky/kernel/probes/kprobes.c | 10 ----------
> arch/ia64/kernel/kprobes.c | 9 ---------
> arch/mips/kernel/kprobes.c | 3 ---
> arch/powerpc/kernel/kprobes.c | 10 ----------
> arch/riscv/kernel/probes/kprobes.c | 10 ----------
> arch/s390/kernel/kprobes.c | 10 ----------
> arch/sh/kernel/kprobes.c | 10 ----------
> arch/sparc/kernel/kprobes.c | 10 ----------
> arch/x86/kernel/kprobes/core.c | 10 ----------
> include/linux/kprobes.h | 8 --------
> kernel/kprobes.c | 19 -------------------
> samples/kprobes/kprobe_example.c | 15 ---------------
> 16 files changed, 5 insertions(+), 172 deletions(-)
>
<snip>
> --- a/arch/x86/kernel/kprobes/core.c
> +++ b/arch/x86/kernel/kprobes/core.c
> @@ -947,16 +947,6 @@ int kprobe_fault_handler(struct pt_regs
> * these specific fault cases.
> */
> kprobes_inc_nmissed_count(cur);
Not necessarily related, but I'm wondering why we're incrementing the
probe miss count here. Unlike what the comment above indicates, this is
not a 'fault' counter, but just a count of the number of times the probe
handler wasn't called.
> -
> - /*
> - * We come here because instructions in the pre/post
> - * handler caused the page_fault, this could happen
> - * if handler tries to access user space by
> - * copy_from_user(), get_user() etc. Let the
> - * user-specified handler try to fix it first.
> - */
> - if (cur->fault_handler && cur->fault_handler(cur, regs, trapnr))
> - return 1;
> }
- Naveen
next prev parent reply other threads:[~2021-05-26 10:51 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-25 7:25 [PATCH 0/2] kprobes: Remove kprobe::fault_handler Peter Zijlstra
2021-05-25 7:25 ` [PATCH 1/2] " Peter Zijlstra
2021-05-25 14:06 ` Masami Hiramatsu
2021-05-26 10:50 ` Naveen N. Rao [this message]
2021-05-26 13:51 ` Masami Hiramatsu
2021-06-01 12:01 ` [PATCH] kprobes: Do not increment probe miss count in the fault handler Naveen N. Rao
2021-06-01 13:20 ` Peter Zijlstra
2021-06-01 23:48 ` Masami Hiramatsu
2021-06-04 13:38 ` [tip: perf/core] " tip-bot2 for Naveen N. Rao
2021-06-01 14:04 ` [tip: perf/core] kprobes: Remove kprobe::fault_handler tip-bot2 for Peter Zijlstra
2021-05-25 7:25 ` [PATCH 2/2] x86,kprobes: WARN if kprobes tries to handle a fault Peter Zijlstra
2021-05-25 14:21 ` Masami Hiramatsu
2021-06-01 14:04 ` [tip: perf/core] " tip-bot2 for Peter Zijlstra
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