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=-10.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=unavailable 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 CE347C433FE for ; Sat, 4 Sep 2021 10:56:08 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B3B806056C for ; Sat, 4 Sep 2021 10:56:08 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1351134AbhIDK5I (ORCPT ); Sat, 4 Sep 2021 06:57:08 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58734 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1351100AbhIDK5H (ORCPT ); Sat, 4 Sep 2021 06:57:07 -0400 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 363C5C061575; Sat, 4 Sep 2021 03:56:05 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=HbnGaf0bnPZtgz30+mN/ev5Nx/MTJPwie3Aor7OwJtk=; b=OfdoP1UUmRFGKnW5MiBcbKdHmh 1gHGW4nZXLEjKgtCMqYzBfmWTMCPsF2R+08DMPa9pRVj+hyfxfikjx9VxLIRm0ZH0YIEXsyExvAtf 15R4onfs3kzAWfDtQUgSt2P7sCV+wUKm5Tm9sh5OREsa9fGNsAmXiVu7m4NG7vUwwX0DgdbAs38mD hC6Y3rNJGPp5uoHD7rQTi1S60oUdGi9LKq+eka5x5R+M6nkwciSDtVFak3bKvmI4Hb/LfPJYX+KtP Ei65lOdmzJilyRor/vqghmiYyt0EgnEG8qTA+/RwAuE8FoxXiKclFwBXNEY7ZBPBm1XbW/CpouHpC 4VGzqMfg==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=worktop.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.94.2 #2 (Red Hat Linux)) id 1mMTKc-005GWI-9s; Sat, 04 Sep 2021 10:55:38 +0000 Received: by worktop.programming.kicks-ass.net (Postfix, from userid 1000) id 9D405986283; Sat, 4 Sep 2021 12:55:29 +0200 (CEST) Date: Sat, 4 Sep 2021 12:55:29 +0200 From: Peter Zijlstra To: Andrii Nakryiko Cc: Song Liu , bpf , open list , Arnaldo Carvalho de Melo , Ingo Molnar , Kajol Jain , Kernel Team Subject: Re: [PATCH v5 bpf-next 2/3] bpf: introduce helper bpf_get_branch_snapshot Message-ID: <20210904105529.GA5106@worktop.programming.kicks-ass.net> References: <20210902165706.2812867-1-songliubraving@fb.com> <20210902165706.2812867-3-songliubraving@fb.com> <20210904102430.GD4323@worktop.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210904102430.GD4323@worktop.programming.kicks-ass.net> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, Sep 04, 2021 at 12:24:30PM +0200, Peter Zijlstra wrote: > On Fri, Sep 03, 2021 at 10:10:16AM -0700, Andrii Nakryiko wrote: > > > I suppose you have to have this helper function because the JIT cannot > > > emit static_call()... although in this case one could cheat and simply > > > emit a call to static_call_query() and not bother with dynamic updates > > > (because there aren't any). > > > > If that's safe, let's do it. > > I'll try and remember to look into static_call_lock(), a means of > forever denying future static_call_update() calls. That should make this > more obvious. A little something like so I suppose.... we don't really have spare bits in the !INLINE case :/ --- diff --git a/include/linux/static_call.h b/include/linux/static_call.h index 3e56a9751c06..b0feccd56d37 100644 --- a/include/linux/static_call.h +++ b/include/linux/static_call.h @@ -174,6 +174,10 @@ struct static_call_tramp_key { s32 key; }; +extern void __static_call_lock(struct static_call_key *key); + +#define static_call_lock(name) __static_call_lock(&STATIC_CALL_KEY(name)) + extern void __static_call_update(struct static_call_key *key, void *tramp, void *func); extern int static_call_mod_init(struct module *mod); extern int static_call_text_reserved(void *start, void *end); @@ -215,6 +219,8 @@ extern long __static_call_return0(void); #elif defined(CONFIG_HAVE_STATIC_CALL) +#define static_call_lock(name) + static inline int static_call_init(void) { return 0; } #define __DEFINE_STATIC_CALL(name, _func, _func_init) \ @@ -268,6 +274,8 @@ static inline long __static_call_return0(void) #else /* Generic implementation */ +#define static_call_lock(name) + static inline int static_call_init(void) { return 0; } static inline long __static_call_return0(void) diff --git a/include/linux/static_call_types.h b/include/linux/static_call_types.h index 5a00b8b2cf9f..e40a3b595c4a 100644 --- a/include/linux/static_call_types.h +++ b/include/linux/static_call_types.h @@ -62,6 +62,7 @@ struct static_call_key { void *func; union { /* bit 0: 0 = mods, 1 = sites */ + /* but 1: locked */ unsigned long type; struct static_call_mod *mods; struct static_call_site *sites; diff --git a/kernel/static_call.c b/kernel/static_call.c index 43ba0b1e0edb..a1ba93fbad29 100644 --- a/kernel/static_call.c +++ b/kernel/static_call.c @@ -104,6 +104,11 @@ static inline bool static_call_key_has_mods(struct static_call_key *key) return !(key->type & 1); } +static inline bool static_call_key_is_locked(struct static_call_key *key) +{ + return !!(key->type & 2); +} + static inline struct static_call_mod *static_call_key_next(struct static_call_key *key) { if (!static_call_key_has_mods(key)) @@ -117,7 +122,7 @@ static inline struct static_call_site *static_call_key_sites(struct static_call_ if (static_call_key_has_mods(key)) return NULL; - return (struct static_call_site *)(key->type & ~1); + return (struct static_call_site *)(key->type & ~3); } void __static_call_update(struct static_call_key *key, void *tramp, void *func) @@ -125,6 +130,9 @@ void __static_call_update(struct static_call_key *key, void *tramp, void *func) struct static_call_site *site, *stop; struct static_call_mod *site_mod, first; + if (WARN_ON_ONCE(static_call_key_is_locked(key))) + return; + cpus_read_lock(); static_call_lock(); @@ -418,6 +426,18 @@ static void static_call_del_module(struct module *mod) } } +void __static_call_lock(struct static_call_key *key) +{ + cpus_read_lock(); + static_call_lock(); + + WARN_ON_ONCE(static_call_key_is_locked(key)); + key->type |= 2; + + static_call_unlock(); + cpus_read_unlock(); +} + static int static_call_module_notify(struct notifier_block *nb, unsigned long val, void *data) {