live-patching.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Steven Rostedt <rostedt@goodmis.org>
To: Miroslav Benes <mbenes@suse.cz>
Cc: 王贇 <yun.wang@linux.alibaba.com>, "Guo Ren" <guoren@kernel.org>,
	"Ingo Molnar" <mingo@redhat.com>,
	"James E.J. Bottomley" <James.Bottomley@HansenPartnership.com>,
	"Helge Deller" <deller@gmx.de>,
	"Michael Ellerman" <mpe@ellerman.id.au>,
	"Benjamin Herrenschmidt" <benh@kernel.crashing.org>,
	"Paul Mackerras" <paulus@samba.org>,
	"Paul Walmsley" <paul.walmsley@sifive.com>,
	"Palmer Dabbelt" <palmer@dabbelt.com>,
	"Albert Ou" <aou@eecs.berkeley.edu>,
	"Thomas Gleixner" <tglx@linutronix.de>,
	"Borislav Petkov" <bp@alien8.de>,
	x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
	"Josh Poimboeuf" <jpoimboe@redhat.com>,
	"Jiri Kosina" <jikos@kernel.org>,
	"Petr Mladek" <pmladek@suse.com>,
	"Joe Lawrence" <joe.lawrence@redhat.com>,
	"Colin Ian King" <colin.king@canonical.com>,
	"Masami Hiramatsu" <mhiramat@kernel.org>,
	"Peter Zijlstra (Intel)" <peterz@infradead.org>,
	"Nicholas Piggin" <npiggin@gmail.com>,
	"Jisheng Zhang" <jszhang@kernel.org>,
	linux-csky@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-parisc@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
	linux-riscv@lists.infradead.org, live-patching@vger.kernel.org
Subject: Re: [PATCH 1/2] ftrace: disable preemption on the testing of recursion
Date: Tue, 12 Oct 2021 08:29:20 -0400	[thread overview]
Message-ID: <20211012082920.1f8d6557@gandalf.local.home> (raw)
In-Reply-To: <alpine.LSU.2.21.2110121421260.3394@pobox.suse.cz>

On Tue, 12 Oct 2021 14:24:43 +0200 (CEST)
Miroslav Benes <mbenes@suse.cz> wrote:

> > +++ b/kernel/livepatch/patch.c
> > @@ -52,11 +52,6 @@ static void notrace klp_ftrace_handler(unsigned long ip,
> >  	bit = ftrace_test_recursion_trylock(ip, parent_ip);
> >  	if (WARN_ON_ONCE(bit < 0))
> >  		return;
> > -	/*
> > -	 * A variant of synchronize_rcu() is used to allow patching functions
> > -	 * where RCU is not watching, see klp_synchronize_transition().
> > -	 */
> > -	preempt_disable_notrace();
> > 
> >  	func = list_first_or_null_rcu(&ops->func_stack, struct klp_func,
> >  				      stack_node);
> > @@ -120,7 +115,6 @@ static void notrace klp_ftrace_handler(unsigned long ip,
> >  	klp_arch_set_pc(fregs, (unsigned long)func->new_func);
> > 
> >  unlock:
> > -	preempt_enable_notrace();
> >  	ftrace_test_recursion_unlock(bit);
> >  }  
> 
> I don't like this change much. We have preempt_disable there not because 
> of ftrace_test_recursion, but because of RCU. ftrace_test_recursion was 
> added later. Yes, it would work with the change, but it would also hide 
> things which should not be hidden in my opinion.

Agreed, but I believe the change is fine, but requires a nice comment to
explain what you said above.

Thus, before the "ftrace_test_recursion_trylock()" we need:

	/*
	 * The ftrace_test_recursion_trylock() will disable preemption,
	 * which is required for the variant of synchronize_rcu() that is
	 * used to allow patching functions where RCU is not watching.
	 * See klp_synchronize_transition() for more details.
	 */

-- Steve

  reply	other threads:[~2021-10-12 12:29 UTC|newest]

Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-10-12  5:39 [PATCH 0/2] ftrace: make sure preemption disabled on recursion testing 王贇
2021-10-12  5:40 ` [PATCH 1/2] ftrace: disable preemption on the testing of recursion 王贇
2021-10-12 12:17   ` Steven Rostedt
2021-10-13  1:46     ` 王贇
2021-10-12 12:24   ` Miroslav Benes
2021-10-12 12:29     ` Steven Rostedt [this message]
2021-10-13  1:52       ` 王贇
2021-10-13  1:50     ` 王贇
2021-10-13  2:27       ` Steven Rostedt
2021-10-13  2:36         ` 王贇
2021-10-12 12:43   ` Steven Rostedt
2021-10-13  2:04     ` 王贇
2021-10-13  2:30       ` Steven Rostedt
2021-10-13  2:38         ` 王贇
2021-10-12  5:40 ` [PATCH 2/2] ftrace: prevent preemption in perf_ftrace_function_call() 王贇
2021-10-12 11:20   ` Peter Zijlstra
2021-10-13  1:45     ` 王贇
2021-10-12  5:41 ` [PATCH 0/2] ftrace: make sure preemption disabled on recursion testing 王贇
2021-10-13  3:16 ` [PATCH v2 0/2] fix & prevent the missing preemption disabling 王贇
2021-10-13  3:17   ` [PATCH v2 1/2] ftrace: disable preemption between ftrace_test_recursion_trylock/unlock() 王贇
2021-10-13  3:18   ` [PATCH v2 2/2] ftrace: do CPU checking after preemption disabled 王贇
2021-10-13  3:26   ` [PATCH v2 0/2] fix & prevent the missing preemption disabling Steven Rostedt
2021-10-13  3:33     ` 王贇
2021-10-26 23:48 ` [PATCH 0/2] ftrace: make sure preemption disabled on recursion testing Palmer Dabbelt

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=20211012082920.1f8d6557@gandalf.local.home \
    --to=rostedt@goodmis.org \
    --cc=James.Bottomley@HansenPartnership.com \
    --cc=aou@eecs.berkeley.edu \
    --cc=benh@kernel.crashing.org \
    --cc=bp@alien8.de \
    --cc=colin.king@canonical.com \
    --cc=deller@gmx.de \
    --cc=guoren@kernel.org \
    --cc=hpa@zytor.com \
    --cc=jikos@kernel.org \
    --cc=joe.lawrence@redhat.com \
    --cc=jpoimboe@redhat.com \
    --cc=jszhang@kernel.org \
    --cc=linux-csky@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-parisc@vger.kernel.org \
    --cc=linux-riscv@lists.infradead.org \
    --cc=linuxppc-dev@lists.ozlabs.org \
    --cc=live-patching@vger.kernel.org \
    --cc=mbenes@suse.cz \
    --cc=mhiramat@kernel.org \
    --cc=mingo@redhat.com \
    --cc=mpe@ellerman.id.au \
    --cc=npiggin@gmail.com \
    --cc=palmer@dabbelt.com \
    --cc=paul.walmsley@sifive.com \
    --cc=paulus@samba.org \
    --cc=peterz@infradead.org \
    --cc=pmladek@suse.com \
    --cc=tglx@linutronix.de \
    --cc=x86@kernel.org \
    --cc=yun.wang@linux.alibaba.com \
    --subject='Re: [PATCH 1/2] ftrace: disable preemption on the testing of recursion' \
    /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).