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=-8.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 728BEC33CAF for ; Thu, 16 Jan 2020 17:44:11 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 42F7D24758 for ; Thu, 16 Jan 2020 17:44:11 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1579196651; bh=JF0ccaR7qzma6RZnVGAc0QY3jNY3PjqO4TYu3jZ7p04=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:List-ID: From; b=QjhVUVKp6V6rTR0btkhGfjUN9fJnbTwYIV3T1VHYFZlZBwdDPiv+Wt7TarF8BvXhC Ijz7NrWWcc9aQ48GW90c8Z09NGdN9JNVBG6fRnTrCHxUhg5vzCXMwxNDkS9cAXJS46 wviFI7Cx4zjbKRP3uzdCebmWEwvKeW2vTKyeAebg= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2394080AbgAPRoK (ORCPT ); Thu, 16 Jan 2020 12:44:10 -0500 Received: from mail.kernel.org ([198.145.29.99]:34150 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2388744AbgAPRnq (ORCPT ); Thu, 16 Jan 2020 12:43:46 -0500 Received: from paulmck-ThinkPad-P72.home (50-39-105-78.bvtn.or.frontiernet.net [50.39.105.78]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 9268B2474E; Thu, 16 Jan 2020 17:43:45 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1579196625; bh=JF0ccaR7qzma6RZnVGAc0QY3jNY3PjqO4TYu3jZ7p04=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=zQnA9E92vc7DPGCkFsxiZ+rKqrIhHx4ZP5aa/0xDqCll//Ryr6P2X8FnsmYHsb1mT fCPh35oc0NLpfw0YceFHulh/5Hf6cPS5imsVQPgZrjNY3S9XcxIEGEnJoIciKTgUcD gAbvv/jdRIJ7a6NiuNcKh+GeBrf6RCgIMM/cdd1c= Received: by paulmck-ThinkPad-P72.home (Postfix, from userid 1000) id 15F6E35227B9; Thu, 16 Jan 2020 09:43:44 -0800 (PST) Date: Thu, 16 Jan 2020 09:43:44 -0800 From: "Paul E. McKenney" To: Marco Elver Cc: andreyknvl@google.com, glider@google.com, dvyukov@google.com, kasan-dev@googlegroups.com, linux-kernel@vger.kernel.org, peterz@infradead.org, mingo@redhat.com, will@kernel.org, Qian Cai Subject: Re: [PATCH -rcu v2] kcsan: Make KCSAN compatible with lockdep Message-ID: <20200116174344.GV2935@paulmck-ThinkPad-P72> Reply-To: paulmck@kernel.org References: <20200115162512.70807-1-elver@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200115162512.70807-1-elver@google.com> User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jan 15, 2020 at 05:25:12PM +0100, Marco Elver wrote: > We must avoid any recursion into lockdep if KCSAN is enabled on > utilities used by lockdep. One manifestation of this is corrupting > lockdep's IRQ trace state (if TRACE_IRQFLAGS). Fix this by: > > 1. Using raw_local_irq{save,restore} in kcsan_setup_watchpoint(). > 2. Disabling lockdep in kcsan_report(). > > Tested with: > > CONFIG_LOCKDEP=y > CONFIG_DEBUG_LOCKDEP=y > CONFIG_TRACE_IRQFLAGS=y > > Where previously, the following warning (and variants with different > stack traces) was consistently generated, with the fix introduced in > this patch, the warning cannot be reproduced. I added Vlad's ack and Qian's Tested-by and queued this. Thank you all! Thanx, Paul > WARNING: CPU: 0 PID: 2 at kernel/locking/lockdep.c:4406 check_flags.part.0+0x101/0x220 > Modules linked in: > CPU: 0 PID: 2 Comm: kthreadd Not tainted 5.5.0-rc1+ #11 > Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.12.0-1 04/01/2014 > RIP: 0010:check_flags.part.0+0x101/0x220 > > Call Trace: > lock_is_held_type+0x69/0x150 > freezer_fork+0x20b/0x370 > cgroup_post_fork+0x2c9/0x5c0 > copy_process+0x2675/0x3b40 > _do_fork+0xbe/0xa30 > ? _raw_spin_unlock_irqrestore+0x40/0x50 > ? match_held_lock+0x56/0x250 > ? kthread_park+0xf0/0xf0 > kernel_thread+0xa6/0xd0 > ? kthread_park+0xf0/0xf0 > kthreadd+0x321/0x3d0 > ? kthread_create_on_cpu+0x130/0x130 > ret_from_fork+0x3a/0x50 > irq event stamp: 64 > hardirqs last enabled at (63): [] _raw_spin_unlock_irqrestore+0x40/0x50 > hardirqs last disabled at (64): [] kcsan_setup_watchpoint+0x92/0x460 > softirqs last enabled at (32): [] fpu__copy+0xe8/0x470 > softirqs last disabled at (30): [] fpu__copy+0x69/0x470 > > Reported-by: Qian Cai > Signed-off-by: Marco Elver > --- > v2: > * Update comments. > --- > kernel/kcsan/core.c | 6 ++++-- > kernel/kcsan/report.c | 11 +++++++++++ > kernel/locking/Makefile | 3 +++ > 3 files changed, 18 insertions(+), 2 deletions(-) > > diff --git a/kernel/kcsan/core.c b/kernel/kcsan/core.c > index 87bf857c8893..64b30f7716a1 100644 > --- a/kernel/kcsan/core.c > +++ b/kernel/kcsan/core.c > @@ -336,8 +336,10 @@ kcsan_setup_watchpoint(const volatile void *ptr, size_t size, int type) > * CPU-local data accesses), it makes more sense (from a data race > * detection point of view) to simply disable preemptions to ensure > * as many tasks as possible run on other CPUs. > + * > + * Use raw versions, to avoid lockdep recursion via IRQ flags tracing. > */ > - local_irq_save(irq_flags); > + raw_local_irq_save(irq_flags); > > watchpoint = insert_watchpoint((unsigned long)ptr, size, is_write); > if (watchpoint == NULL) { > @@ -429,7 +431,7 @@ kcsan_setup_watchpoint(const volatile void *ptr, size_t size, int type) > > kcsan_counter_dec(KCSAN_COUNTER_USED_WATCHPOINTS); > out_unlock: > - local_irq_restore(irq_flags); > + raw_local_irq_restore(irq_flags); > out: > user_access_restore(ua_flags); > } > diff --git a/kernel/kcsan/report.c b/kernel/kcsan/report.c > index b5b4feea49de..33bdf8b229b5 100644 > --- a/kernel/kcsan/report.c > +++ b/kernel/kcsan/report.c > @@ -2,6 +2,7 @@ > > #include > #include > +#include > #include > #include > #include > @@ -410,6 +411,14 @@ void kcsan_report(const volatile void *ptr, size_t size, int access_type, > { > unsigned long flags = 0; > > + /* > + * With TRACE_IRQFLAGS, lockdep's IRQ trace state becomes corrupted if > + * we do not turn off lockdep here; this could happen due to recursion > + * into lockdep via KCSAN if we detect a data race in utilities used by > + * lockdep. > + */ > + lockdep_off(); > + > kcsan_disable_current(); > if (prepare_report(&flags, ptr, size, access_type, cpu_id, type)) { > if (print_report(ptr, size, access_type, value_change, cpu_id, type) && panic_on_warn) > @@ -418,4 +427,6 @@ void kcsan_report(const volatile void *ptr, size_t size, int access_type, > release_report(&flags, type); > } > kcsan_enable_current(); > + > + lockdep_on(); > } > diff --git a/kernel/locking/Makefile b/kernel/locking/Makefile > index 45452facff3b..6d11cfb9b41f 100644 > --- a/kernel/locking/Makefile > +++ b/kernel/locking/Makefile > @@ -5,6 +5,9 @@ KCOV_INSTRUMENT := n > > obj-y += mutex.o semaphore.o rwsem.o percpu-rwsem.o > > +# Avoid recursion lockdep -> KCSAN -> ... -> lockdep. > +KCSAN_SANITIZE_lockdep.o := n > + > ifdef CONFIG_FUNCTION_TRACER > CFLAGS_REMOVE_lockdep.o = $(CC_FLAGS_FTRACE) > CFLAGS_REMOVE_lockdep_proc.o = $(CC_FLAGS_FTRACE) > -- > 2.25.0.rc1.283.g88dfdc4193-goog >