linux-kernel.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
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


  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] " 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

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=1622025445.6q8nl3t4ap.naveen@linux.ibm.com \
    --to=naveen.n.rao@linux.vnet.ibm.com \
    --cc=ananth@linux.ibm.com \
    --cc=hch@lst.de \
    --cc=linux-kernel@vger.kernel.org \
    --cc=mhiramat@kernel.org \
    --cc=mingo@kernel.org \
    --cc=peterz@infradead.org \
    --cc=rostedt@goodmis.org \
    --cc=x86@kernel.org \
    --subject='Re: [PATCH 1/2] kprobes: Remove kprobe::fault_handler' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).