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
next prev parent 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
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