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 bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 2B42BC433EF for ; Sun, 1 May 2022 14:10:34 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject:Cc:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=d/JdesCzRlSlRQVbh/2tVWLan/hTOKnjt6y/lg8+xAE=; b=SuW7ttdecCM5gc eg1Ci/foCkZ0cDVTHQuf/milWZS0U3kU3uwwtxdIwow6BSc6x9Y6ecr04klWScJ7KveQmVDh8+DJK 7iDL8tHHN2Syef0dUNbFcR725ANe+C5jJulofbpAvNDpw5A4bBqU5fZCUQDjBIsSgMO3KfEiqkp+P FQICY+2T3hZq0a/MPyWsjCsxUVIsqsoxv4VbnaSaQljdFnR4ng4OxTVCl3qY6wctMhnz/18xDcZb/ zPrkTOh/r1E91j6iVFANNsz4tzTsTGr8PskKnFWSBu2ihw5kZpbLh5Tw5Ss2BdLs+pFutNMNfu4qY amsCLyHvB0z8yP/834cQ==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1nlAH9-00GR25-VM; Sun, 01 May 2022 14:10:15 +0000 Received: from mail-qt1-x836.google.com ([2607:f8b0:4864:20::836]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1nlAH3-00GR1F-O5 for linux-riscv@lists.infradead.org; Sun, 01 May 2022 14:10:11 +0000 Received: by mail-qt1-x836.google.com with SMTP id y3so9574625qtn.8 for ; Sun, 01 May 2022 07:10:04 -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=3Sm9UXu9dl/CUBJSuaBhyUQljsx3yOZ06jYECR4NTRAmGX4+hX8QCfxjM2Cb4r2DWg K78dy44+19NLdENjDNK/mIsaqp3EhzjWl+IxcR5+l9Mnp2H8wQtffbPy2gVHsrIv6wzT KJXaNBmlJBPkJzZQl5HOCsb63+7e7jg7/S1FZ2z1nKmzZncgpZa/blNv8a173qZnx40p tTdI+/CA/lfaEZ1OCD9cynqxW1tEN1ei+WM2P4yybyjZXItblDpqOGvDlIMGnWq78Vye Qh3YARRu6r40StLRswkD/Yp44Sz2Db9if9MhIhZGfaoeb30AXN88gOt61eyJEXzI3anZ QUvg== X-Gm-Message-State: AOAM531nou/GL90kB9bj1h0bcG8McoeyMsBReXjKHmnqBNxDvc5d5VOn wHBXPzsSpnOupYE1ql3mCgA= 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-Disposition: inline In-Reply-To: <20220322022331.32136-1-palmer@rivosinc.com> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20220501_071009_845929_476ACF70 X-CRM114-Status: GOOD ( 30.44 ) X-BeenThere: linux-riscv@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-riscv" Errors-To: linux-riscv-bounces+linux-riscv=archiver.kernel.org@lists.infradead.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 _______________________________________________ linux-riscv mailing list linux-riscv@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-riscv