From: Petr Mladek <pmladek@suse.com>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: LKML <linux-kernel@vger.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>,
"Miroslav Benes" <mbenes@suse.cz>,
"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-parisc@vger.kernel.org,
linuxppc-dev@lists.ozlabs.org, linux-riscv@lists.infradead.org,
live-patching@vger.kernel.org, 王贇 <yun.wang@linux.alibaba.com>,
"Guo Ren" <guoren@kernel.org>
Subject: Re: [PATCH] tracing: Have all levels of checks prevent recursion
Date: Tue, 19 Oct 2021 08:41:23 +0200 [thread overview]
Message-ID: <YW5ok3CfNoRMfVQ5@alley> (raw)
In-Reply-To: <20211018220203.064a42ed@gandalf.local.home>
On Mon 2021-10-18 22:02:03, Steven Rostedt wrote:
> On Mon, 18 Oct 2021 12:19:20 +0200
> Petr Mladek <pmladek@suse.com> wrote:
>
> > > -
> > > bit = trace_get_context_bit() + start;
> > > if (unlikely(val & (1 << bit))) {
> > > /*
> > > * It could be that preempt_count has not been updated during
> > > * a switch between contexts. Allow for a single recursion.
> > > */
> > > - bit = TRACE_TRANSITION_BIT;
> > > + bit = TRACE_CTX_TRANSITION + start;
> >
>
> [..]
>
> > Could we please update the comment? I mean to say if it is a race
> > or if we trace a function that should not get traced.
>
> What do you think of this change?
>
> diff --git a/include/linux/trace_recursion.h b/include/linux/trace_recursion.h
> index 1d8cce02c3fb..24f284eb55a7 100644
> --- a/include/linux/trace_recursion.h
> +++ b/include/linux/trace_recursion.h
> @@ -168,8 +168,12 @@ static __always_inline int trace_test_and_set_recursion(unsigned long ip, unsign
> bit = trace_get_context_bit() + start;
> if (unlikely(val & (1 << bit))) {
> /*
> - * It could be that preempt_count has not been updated during
> - * a switch between contexts. Allow for a single recursion.
> + * If an interrupt occurs during a trace, and another trace
> + * happens in that interrupt but before the preempt_count is
> + * updated to reflect the new interrupt context, then this
> + * will think a recursion occurred, and the event will be dropped.
> + * Let a single instance happen via the TRANSITION_BIT to
> + * not drop those events.
> */
> bit = TRACE_TRANSITION_BIT;
> if (val & (1 << bit)) {
>
>
Looks good to me. Thanks for the update.
Feel free to postpone this change. I do not want to complicate
upstreaming the fix for stable. I am sorry if I already
complicated it.
Best Regards,
Petr
next prev parent reply other threads:[~2021-10-19 6:41 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-10-15 15:00 [PATCH] tracing: Have all levels of checks prevent recursion Steven Rostedt
2021-10-15 16:17 ` Peter Zijlstra
2021-10-15 17:35 ` Steven Rostedt
2021-10-15 17:58 ` Steven Rostedt
2021-10-15 18:04 ` Peter Zijlstra
2021-10-15 18:20 ` Steven Rostedt
2021-10-15 18:24 ` Peter Zijlstra
2021-10-15 19:00 ` Steven Rostedt
2021-10-15 18:25 ` Steven Rostedt
2023-07-21 15:34 ` Alexander Lobakin
2023-07-21 16:00 ` Steven Rostedt
2023-07-21 16:06 ` Alexander Lobakin
2023-07-21 16:26 ` Steven Rostedt
2023-07-22 1:22 ` Jakub Kicinski
2021-10-18 10:19 ` Petr Mladek
2021-10-18 13:50 ` Steven Rostedt
2021-10-18 15:09 ` Petr Mladek
2021-10-19 2:02 ` Steven Rostedt
2021-10-19 6:41 ` Petr Mladek [this message]
2021-10-19 13:00 ` Steven Rostedt
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