From: Miroslav Benes <mbenes@suse.cz>
To: 王贇 <yun.wang@linux.alibaba.com>
Cc: Guo Ren <guoren@kernel.org>, Steven Rostedt <rostedt@goodmis.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 14:24:43 +0200 (CEST) [thread overview]
Message-ID: <alpine.LSU.2.21.2110121421260.3394@pobox.suse.cz> (raw)
In-Reply-To: <a8756482-024c-c858-b3d1-1ffa9a5eb3f7@linux.alibaba.com>
> diff --git a/include/linux/trace_recursion.h b/include/linux/trace_recursion.h
> index a9f9c57..805f9c4 100644
> --- a/include/linux/trace_recursion.h
> +++ b/include/linux/trace_recursion.h
> @@ -214,7 +214,14 @@ static __always_inline void trace_clear_recursion(int bit)
> static __always_inline int ftrace_test_recursion_trylock(unsigned long ip,
> unsigned long parent_ip)
> {
> - return trace_test_and_set_recursion(ip, parent_ip, TRACE_FTRACE_START, TRACE_FTRACE_MAX);
> + int bit;
> +
> + preempt_disable_notrace();
> + bit = trace_test_and_set_recursion(ip, parent_ip, TRACE_FTRACE_START, TRACE_FTRACE_MAX);
> + if (bit < 0)
> + preempt_enable_notrace();
> +
> + return bit;
> }
>
> /**
> @@ -226,6 +233,7 @@ static __always_inline int ftrace_test_recursion_trylock(unsigned long ip,
> static __always_inline void ftrace_test_recursion_unlock(int bit)
> {
> trace_clear_recursion(bit);
> + preempt_enable_notrace();
> }
>
> #endif /* CONFIG_TRACING */
> diff --git a/kernel/livepatch/patch.c b/kernel/livepatch/patch.c
> index e8029ae..6e66ccd 100644
> --- a/kernel/livepatch/patch.c
> +++ 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.
Miroslav
next prev parent reply other threads:[~2021-10-12 12:24 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 [this message]
2021-10-12 12:29 ` Steven Rostedt
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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