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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 5B7AAC433F5 for ; Sun, 1 May 2022 14:10:20 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S240427AbiEAONd (ORCPT ); Sun, 1 May 2022 10:13:33 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:47448 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230014AbiEAONb (ORCPT ); Sun, 1 May 2022 10:13:31 -0400 Received: from mail-qt1-x82a.google.com (mail-qt1-x82a.google.com [IPv6:2607:f8b0:4864:20::82a]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 0B44513D13 for ; Sun, 1 May 2022 07:10:05 -0700 (PDT) Received: by mail-qt1-x82a.google.com with SMTP id o11so9547110qtp.13 for ; Sun, 01 May 2022 07:10:05 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=BRwGtOiAYfwSN6Oles1YkgeEY1NKrbkCB/10eptXYYY=; b=ClFxWUjH8XMA/vgyIe0hQoH/MzjY7rMmcS4ORgWAsYLQMdB11XCi+8aDZo5xJHxoia rGUM3u8GjHZzPvRLqInRjExs8EXMTpVvq3UyPI35dr20I+Pgss217fMN4CB1QPDUF2P7 jqbGaf/CSr0/vxi50FnsoKOypQITAUMKcbsliEZW2GnvNnakXXqlRquIskrv9hG6ZnKB Wra+6tDrbA3taShQH7U8Pvjiav2Xbvo+W6GxaxcjON+1kWo8hzCzrj/TeYY/B25/WxSm kCUm7A1y54+VXBprfqyef9JLQz4Yei7i4EqNgf75MlR3duwRaj4R7QR2SNOTADEqLkvK onDA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=BRwGtOiAYfwSN6Oles1YkgeEY1NKrbkCB/10eptXYYY=; b=RvYEAeGHgxgxdzFkHaVLgwaf2kg16CaYgNq17BWBnuejLyqhYqVYkGLUczIwAERbuW ifWcGL8r+heY8RnRBe5GWxgWs2K5gI3jvaouWInmVEAVdXpyuO1mf8lPF4iNowvUduBx +QPV6dOoLMy4rc23ZdZnH+9D6zNZicBGLPppHtWKJTTrDllNd8yQiEtQP222dEYaryuW tFVCgIBPAPcXs3G8GX3iYVpfC+RRO08f6Cx/a7envKyJDiF/fkzo1QSo8iWbDxL72ERR qHxgsAK+O6MYMGXPMG2pAEAdxW/E3NRIS8cUBX21nqRkzYIwCZDQ7G4gPnRtwC20K5WS 7iWA== X-Gm-Message-State: AOAM532hFyjHCQpCVTwhAYLca2W+gBqrt02Ec4fEh374QxPcnYvz8hyf laGF70h2Of8wiglcvapjoqQ= X-Google-Smtp-Source: ABdhPJxPM2isTbHISz0t0AcLxXTLolOd3oSBp6e9+AzqjOY7OiPXahL7T0OmhvO4YXUviKQdBzYLSQ== X-Received: by 2002:a05:622a:5d0:b0:2e1:d430:a5c9 with SMTP id d16-20020a05622a05d000b002e1d430a5c9mr6931254qtb.639.1651414204081; Sun, 01 May 2022 07:10:04 -0700 (PDT) Received: from mail.google.com ([207.246.89.135]) by smtp.gmail.com with ESMTPSA id g20-20020ac84694000000b002f39b99f6b6sm2688086qto.80.2022.05.01.07.09.56 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 01 May 2022 07:10:03 -0700 (PDT) Date: Sun, 1 May 2022 22:09:53 +0800 From: Changbin Du To: Palmer Dabbelt Cc: linux-riscv@lists.infradead.org, changbin.du@gmail.com, rostedt@goodmis.org, mingo@redhat.com, Paul Walmsley , Palmer Dabbelt , aou@eecs.berkeley.edu, linux-kernel@vger.kernel.org, Palmer Dabbelt Subject: Re: [PATCH] RISC-V: Don't check text_mutex during stop_machine Message-ID: <20220501140953.3dkqa6jhkcxzammq@mail.google.com> References: <20220322022331.32136-1-palmer@rivosinc.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220322022331.32136-1-palmer@rivosinc.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Mar 21, 2022 at 07:23:31PM -0700, Palmer Dabbelt wrote: > From: Palmer Dabbelt > > We're currently using stop_machine() to update ftrace, which means that > the thread that takes text_mutex during ftrace_prepare() may not be the > same as the thread that eventually patches the code. This isn't > actually a race because the lock is still held (preventing any other > concurrent accesses) and there is only one thread running during > stop_machine(), but it does trigger a lockdep failure. > > This patch just elides the lockdep check during stop_machine. > > Fixes: c15ac4fd60d5 ("riscv/ftrace: Add dynamic function tracer support") > Suggested-by: Steven Rostedt > Reported-by: Changbin Du > Signed-off-by: Palmer Dabbelt > Signed-off-by: Palmer Dabbelt > > -- > > Changes since v1 [<20210506071041.417854-1-palmer@dabbelt.com>]: > * Use ftrace_arch_ocde_modify_{prepare,post_process}() to set the flag. > I remember having a reason I wanted the function when I wrote the v1, > but it's been almost a year and I forget what that was -- maybe I was > just crazy, the patch was sent at midnight. > * Fix DYNAMIC_FTRACE=n builds. > --- > arch/riscv/include/asm/ftrace.h | 7 +++++++ > arch/riscv/kernel/ftrace.c | 12 ++++++++++++ > arch/riscv/kernel/patch.c | 10 +++++++++- > 3 files changed, 28 insertions(+), 1 deletion(-) > > diff --git a/arch/riscv/include/asm/ftrace.h b/arch/riscv/include/asm/ftrace.h > index 04dad3380041..3ac7609f4ee9 100644 > --- a/arch/riscv/include/asm/ftrace.h > +++ b/arch/riscv/include/asm/ftrace.h > @@ -81,8 +81,15 @@ do { \ > struct dyn_ftrace; > int ftrace_init_nop(struct module *mod, struct dyn_ftrace *rec); > #define ftrace_init_nop ftrace_init_nop > +extern int riscv_ftrace_in_stop_machine; > #endif > > +#else /* CONFIG_DYNAMIC_FTRACE */ > + > +#ifndef __ASSEMBLY__ > +#define riscv_ftrace_in_stop_machine 0 > #endif > > +#endif /* CONFIG_DYNAMIC_FTRACE */ > + > #endif /* _ASM_RISCV_FTRACE_H */ > diff --git a/arch/riscv/kernel/ftrace.c b/arch/riscv/kernel/ftrace.c > index 4716f4cdc038..c5f77922d7ea 100644 > --- a/arch/riscv/kernel/ftrace.c > +++ b/arch/riscv/kernel/ftrace.c > @@ -11,15 +11,27 @@ > #include > #include > > +int riscv_ftrace_in_stop_machine; > + > #ifdef CONFIG_DYNAMIC_FTRACE > int ftrace_arch_code_modify_prepare(void) __acquires(&text_mutex) > { > mutex_lock(&text_mutex); > + > + /* > + * The code sequences we use for ftrace can't be patched while the > + * kernel is running, so we need to use stop_machine() to modify them > + * for now. This doesn't play nice with text_mutex, we use this flag > + * to elide the check. > + */ > + riscv_ftrace_in_stop_machine = true; > + > return 0; > } > > int ftrace_arch_code_modify_post_process(void) __releases(&text_mutex) > { > + riscv_ftrace_in_stop_machine = false; > mutex_unlock(&text_mutex); > return 0; > } The function ftrace_init_nop() should be updated. That's not in stop-machine context. @@ -136,9 +124,9 @@ int ftrace_init_nop(struct module *mod, struct dyn_ftrace *rec) { int out; - ftrace_arch_code_modify_prepare(); + mutex_lock(&text_mutex); out = ftrace_make_nop(mod, rec, MCOUNT_ADDR); - ftrace_arch_code_modify_post_process(); + mutex_unlock(&text_mutex); -- Cheers, Changbin Du