From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-9.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id EE6A4C433E1 for ; Mon, 17 Aug 2020 21:23:06 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id B2B0420674 for ; Mon, 17 Aug 2020 21:23:06 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org B2B0420674 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=linux.intel.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 382B46B0003; Mon, 17 Aug 2020 17:23:06 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 30BFC6B0005; Mon, 17 Aug 2020 17:23:06 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 1D5FD8D0002; Mon, 17 Aug 2020 17:23:06 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0247.hostedemail.com [216.40.44.247]) by kanga.kvack.org (Postfix) with ESMTP id 032906B0003 for ; Mon, 17 Aug 2020 17:23:05 -0400 (EDT) Received: from smtpin05.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay05.hostedemail.com (Postfix) with ESMTP id A4915181AEF39 for ; Mon, 17 Aug 2020 21:23:05 +0000 (UTC) X-FDA: 77161335930.05.aunt00_2a0ef3b27019 Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin05.hostedemail.com (Postfix) with ESMTP id 6F6D31826B6B2 for ; Mon, 17 Aug 2020 21:23:05 +0000 (UTC) X-HE-Tag: aunt00_2a0ef3b27019 X-Filterd-Recvd-Size: 6674 Received: from mga11.intel.com (mga11.intel.com [192.55.52.93]) by imf40.hostedemail.com (Postfix) with ESMTP for ; Mon, 17 Aug 2020 21:23:04 +0000 (UTC) IronPort-SDR: 6yPvpuHWrkamRFuaaAuYNwAK1Qx3jO5OjP+DY54g6b/6id0ORt57qZms1tSjAvl0ARiLiNSxp+ fXGUjW3BHlhA== X-IronPort-AV: E=McAfee;i="6000,8403,9716"; a="152428429" X-IronPort-AV: E=Sophos;i="5.76,324,1592895600"; d="scan'208";a="152428429" X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga005.jf.intel.com ([10.7.209.41]) by fmsmga102.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 17 Aug 2020 14:23:02 -0700 IronPort-SDR: bNgMPOd0bydM3J0KCY8Xabznvg129yOoxk2IAxZVPZUY24Y7HV5WW6eocNjxK2I47PAk1scGq6 KefseTSFyr0g== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.76,324,1592895600"; d="scan'208";a="471561454" Received: from bbartede-mobl.ger.corp.intel.com (HELO localhost) ([10.249.32.24]) by orsmga005.jf.intel.com with ESMTP; 17 Aug 2020 14:22:59 -0700 Date: Tue, 18 Aug 2020 00:22:58 +0300 From: Jarkko Sakkinen To: Masami Hiramatsu Cc: Ingo Molnar , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Andi Kleen , Peter Zijlstra , Jessica Yu , "Naveen N. Rao" , Anil S Keshavamurthy , "David S. Miller" , Steven Rostedt , Ingo Molnar Subject: Re: [PATCH v5 1/6] kprobes: Remove dependency to the module_mutex Message-ID: <20200817212258.GD44714@linux.intel.com> References: <20200724050553.1724168-1-jarkko.sakkinen@linux.intel.com> <20200724050553.1724168-2-jarkko.sakkinen@linux.intel.com> <20200724091711.GB517988@gmail.com> <20200725030107.GF17052@linux.intel.com> <20200725102110.GA757173@gmail.com> <20200728163400.e00b09c594763349f99ce6cb@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200728163400.e00b09c594763349f99ce6cb@kernel.org> Organization: Intel Finland Oy - BIC 0357606-4 - Westendinkatu 7, 02160 Espoo X-Rspamd-Queue-Id: 6F6D31826B6B2 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam03 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Tue, Jul 28, 2020 at 04:34:00PM +0900, Masami Hiramatsu wrote: > On Sat, 25 Jul 2020 12:21:10 +0200 > Ingo Molnar wrote: > > > > > * Jarkko Sakkinen wrote: > > > > > On Fri, Jul 24, 2020 at 11:17:11AM +0200, Ingo Molnar wrote: > > > > > > > > * Jarkko Sakkinen 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 > 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 > Signed-off-by: Masami Hiramatsu > --- > 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