From: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
To: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Ingo Molnar <mingo@kernel.org>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org,
Andi Kleen <ak@linux.intel.com>,
Peter Zijlstra <peterz@infradead.org>,
Jessica Yu <jeyu@kernel.org>,
"Naveen N. Rao" <naveen.n.rao@linux.ibm.com>,
Anil S Keshavamurthy <anil.s.keshavamurthy@intel.com>,
"David S. Miller" <davem@davemloft.net>,
Steven Rostedt <rostedt@goodmis.org>,
Ingo Molnar <mingo@redhat.com>
Subject: Re: [PATCH v5 1/6] kprobes: Remove dependency to the module_mutex
Date: Tue, 18 Aug 2020 00:22:58 +0300 [thread overview]
Message-ID: <20200817212258.GD44714@linux.intel.com> (raw)
In-Reply-To: <20200728163400.e00b09c594763349f99ce6cb@kernel.org>
On Tue, Jul 28, 2020 at 04:34:00PM +0900, Masami Hiramatsu wrote:
> On Sat, 25 Jul 2020 12:21:10 +0200
> Ingo Molnar <mingo@kernel.org> wrote:
>
> >
> > * Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com> wrote:
> >
> > > On Fri, Jul 24, 2020 at 11:17:11AM +0200, Ingo Molnar wrote:
> > > >
> > > > * Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com> wrote:
> > > >
> > > > > --- a/kernel/kprobes.c
> > > > > +++ b/kernel/kprobes.c
> > > > > @@ -564,7 +564,7 @@ static void kprobe_optimizer(struct work_struct *work)
> > > > > cpus_read_lock();
> > > > > mutex_lock(&text_mutex);
> > > > > /* Lock modules while optimizing kprobes */
> > > > > - mutex_lock(&module_mutex);
> > > > > + lock_modules();
> > > > >
> > > > > /*
> > > > > * Step 1: Unoptimize kprobes and collect cleaned (unused and disarmed)
> > > > > @@ -589,7 +589,7 @@ static void kprobe_optimizer(struct work_struct *work)
> > > > > /* Step 4: Free cleaned kprobes after quiesence period */
> > > > > do_free_cleaned_kprobes();
> > > > >
> > > > > - mutex_unlock(&module_mutex);
> > > > > + unlock_modules();
> > > > > mutex_unlock(&text_mutex);
> > > > > cpus_read_unlock();
> > > >
> > > > BTW., it would be nice to expand on the comments above - exactly which
> > > > parts of the modules code is being serialized against and why?
> > > >
> > > > We already hold the text_mutex here, which should protect against most
> > > > kprobes related activities interfering - and it's unclear (to me)
> > > > which part of the modules code is being serialized with here, and the
> > > > 'lock modules while optimizing kprobes' comments is unhelpful. :-)
> > > >
> > > > Thanks,
> > > >
> > > > Ingo
> > >
> > > AFAIK, only if you need to call find_module(), you ever need to acquire
> > > this mutex. 99% of time it is internally taken care by kernel/module.c.
> > >
> > > I cannot make up any obvious reason to acquire it here.
> >
> > If it's unnecessary, then it needs to be removed.
> >
> > If it's necessary, then it needs to be documented better.
>
> Good catch! This is not needed anymore.
> It has been introduced to avoid conflict with text modification, at that
> point we didn't get text_mutex. But after commit f1c6ece23729 ("kprobes: Fix
> potential deadlock in kprobe_optimizer()") moved the text_mutex in the current
> position, we don't need it. (and anyway, keeping kprobe_mutex locked means
> any module unloading will be stopped inside kprobes_module_callback())
>
> This may help?
Hey, thanks a lot. This will help to clean my patch set. I'll send a
follow up version as soon I'm on track with my work. I have to recall
my set of changes and backtrack some of the discussion.
I was two weeks in vacation and last week had bunch of network
connectivity issues last week. Anyway, enough time for details to fade
away :-)
/Jarkko
>
> From 2355ecd941c3234b12a6de7443592848ed4e2087 Mon Sep 17 00:00:00 2001
> From: Masami Hiramatsu <mhiramat@kernel.org>
> Date: Tue, 28 Jul 2020 16:32:34 +0900
> Subject: [PATCH] kprobes: Remove unneeded module_mutex lock from the optimizer
>
> Remove unneeded module_mutex locking from the optimizer. Since
> we already locks both kprobe_mutex and text_mutex in the optimizer,
> text will not be changed and the module unloading will be stopped
> inside kprobes_module_callback().
>
> Suggested-by: Ingo Molnar <mingo@kernel.org>
> Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
> ---
> kernel/kprobes.c | 3 ---
> 1 file changed, 3 deletions(-)
>
> diff --git a/kernel/kprobes.c b/kernel/kprobes.c
> index 4a904cc56d68..d1b02e890793 100644
> --- a/kernel/kprobes.c
> +++ b/kernel/kprobes.c
> @@ -563,8 +563,6 @@ static void kprobe_optimizer(struct work_struct *work)
> mutex_lock(&kprobe_mutex);
> cpus_read_lock();
> mutex_lock(&text_mutex);
> - /* Lock modules while optimizing kprobes */
> - mutex_lock(&module_mutex);
>
> /*
> * Step 1: Unoptimize kprobes and collect cleaned (unused and disarmed)
> @@ -589,7 +587,6 @@ static void kprobe_optimizer(struct work_struct *work)
> /* Step 4: Free cleaned kprobes after quiesence period */
> do_free_cleaned_kprobes();
>
> - mutex_unlock(&module_mutex);
> mutex_unlock(&text_mutex);
> cpus_read_unlock();
>
> --
> 2.25.1
> --
> Masami Hiramatsu <mhiramat@kernel.org>
next prev parent reply other threads:[~2020-08-17 21:23 UTC|newest]
Thread overview: 47+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-24 5:05 [PATCH v5 0/6] arch/x86: kprobes: Remove MODULES dependency Jarkko Sakkinen
2020-07-24 5:05 ` [PATCH v5 1/6] kprobes: Remove dependency to the module_mutex Jarkko Sakkinen
2020-07-24 9:13 ` Ingo Molnar
2020-07-25 2:36 ` Jarkko Sakkinen
2020-07-24 9:17 ` Ingo Molnar
2020-07-25 3:01 ` Jarkko Sakkinen
2020-07-25 10:21 ` Ingo Molnar
2020-07-28 7:34 ` Masami Hiramatsu
2020-07-28 12:29 ` [tip: perf/core] kprobes: Remove unnecessary module_mutex locking from kprobe_optimizer() tip-bot2 for Masami Hiramatsu
2020-08-17 21:22 ` Jarkko Sakkinen [this message]
2020-07-24 10:22 ` [PATCH v5 1/6] kprobes: Remove dependency to the module_mutex Mike Rapoport
2020-07-25 2:42 ` Jarkko Sakkinen
2020-07-24 14:46 ` Masami Hiramatsu
2020-07-25 2:48 ` Jarkko Sakkinen
2020-07-24 5:05 ` [PATCH v5 2/6] vmalloc: Add text_alloc() and text_free() Jarkko Sakkinen
2020-07-24 10:22 ` Mike Rapoport
2020-07-25 2:20 ` Jarkko Sakkinen
2020-07-24 5:05 ` [PATCH v5 3/6] arch/x86: Implement " Jarkko Sakkinen
2020-07-24 9:22 ` Ingo Molnar
2020-07-25 2:03 ` Jarkko Sakkinen
2020-07-24 5:05 ` [PATCH v5 4/6] arch/x86: kprobes: Use " Jarkko Sakkinen
2020-07-24 5:05 ` [PATCH v5 5/6] " Jarkko Sakkinen
2020-07-24 9:27 ` Ingo Molnar
2020-07-24 12:16 ` Ard Biesheuvel
2020-07-25 3:19 ` [PATCH v5 5/6] kprobes: Use text_alloc() and text_free()] Jarkko Sakkinen
2020-07-25 3:16 ` [PATCH v5 5/6] kprobes: Use text_alloc() and text_free() Jarkko Sakkinen
2020-07-26 8:14 ` Mike Rapoport
2020-07-26 16:06 ` Ard Biesheuvel
2020-07-28 8:17 ` Masami Hiramatsu
2020-07-28 10:56 ` Ard Biesheuvel
2020-07-28 13:35 ` Masami Hiramatsu
2020-07-28 17:51 ` Ard Biesheuvel
2020-07-29 1:50 ` Masami Hiramatsu
2020-07-29 6:13 ` Ard Biesheuvel
2020-07-30 1:09 ` Masami Hiramatsu
2020-08-18 5:30 ` Jarkko Sakkinen
2020-08-18 11:51 ` Mike Rapoport
2020-08-18 16:30 ` Jarkko Sakkinen
2020-08-19 6:47 ` Mike Rapoport
2020-08-19 21:07 ` Jarkko Sakkinen
2020-07-24 10:27 ` Mike Rapoport
2020-07-24 14:57 ` Masami Hiramatsu
2020-07-24 23:38 ` Jarkko Sakkinen
2020-07-24 5:05 ` [PATCH v5 6/6] kprobes: Remove CONFIG_MODULES dependency Jarkko Sakkinen
2020-07-24 7:01 ` [PATCH v5 0/6] arch/x86: kprobes: Remove MODULES dependency Jarkko Sakkinen
2020-07-24 10:26 ` Mike Rapoport
-- strict thread matches above, loose matches on Subject: below --
2020-07-24 5:04 Jarkko Sakkinen
2020-07-24 5:04 ` [PATCH v5 1/6] kprobes: Remove dependency to the module_mutex Jarkko Sakkinen
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