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dmarc=none (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20170209; h=Sender: Content-Transfer-Encoding:Content-Type:Cc:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:Date: Message-ID:From:References:To:Subject:Reply-To:Content-ID:Content-Description :Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=ekBshGQoka3kDNBsCeyYrSYIUGhrIZDYZcfAbDfHTaU=; b=hTJyR1aUpzE10z m9Q0ZsCszAz9Yk1wdAntrmj1p3dIwR0dVaKyldmcO0u84FAmmstcugWVP/U+0vBOGiKAg9Y2+SHz/ ig1KQMOWslGaBc0SmbYYF9LeoYIXae2L34DRpOFjiJaA86wA9eqnCV6r/rD76ztvMXX6ucLTCF6zP 9D1F2l+n/VP7TsQGJqGsmiLFe2s6/b36HD8QGH7dgWA5/UzEBhdTRfWXVQ7a96mt+JHJx2d+d6I3f g3qo8JyXhNjji+2SyYe3ZG/eX1C0eauWLE3NLwTrZKyIGoxBjWGmE26hsX2/t2pA4pA1m4N4qDUZH XKulMbVtS1ZhtyL4zCAQ==; Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.90_1 #2 (Red Hat Linux)) id 1gts7c-0001Ra-9E; Wed, 13 Feb 2019 10:50:32 +0000 Received: from usa-sjc-mx-foss1.foss.arm.com ([217.140.101.70] helo=foss.arm.com) by bombadil.infradead.org with esmtp (Exim 4.90_1 #2 (Red Hat Linux)) id 1gts7Y-0001RE-OT for linux-arm-kernel@lists.infradead.org; Wed, 13 Feb 2019 10:50:30 +0000 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 8F295A78; Wed, 13 Feb 2019 02:50:27 -0800 (PST) Received: from [10.1.197.45] (e112298-lin.cambridge.arm.com [10.1.197.45]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 45F683F575; Wed, 13 Feb 2019 02:50:24 -0800 (PST) Subject: Re: [PATCH v3 3/4] uaccess: Check no rescheduling function is called in unsafe region To: Peter Zijlstra References: <1547560709-56207-1-git-send-email-julien.thierry@arm.com> <1547560709-56207-4-git-send-email-julien.thierry@arm.com> <20190211134527.GA121589@gmail.com> <20190211135159.GC32511@hirez.programming.kicks-ass.net> <20190213103553.GO32494@hirez.programming.kicks-ass.net> From: Julien Thierry Message-ID: <1c2429a4-9df9-40a3-98e0-51577de4bd6a@arm.com> Date: Wed, 13 Feb 2019 10:50:21 +0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.2.1 MIME-Version: 1.0 In-Reply-To: <20190213103553.GO32494@hirez.programming.kicks-ass.net> Content-Language: en-US X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20190213_025028_801480_DAF738C5 X-CRM114-Status: GOOD ( 16.51 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: catalin.marinas@arm.com, will.deacon@arm.com, linux-kernel@vger.kernel.org, valentin.schneider@arm.com, mingo@redhat.com, james.morse@arm.com, hpa@zytor.com, Ingo Molnar , linux-arm-kernel@lists.infradead.org Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 13/02/2019 10:35, Peter Zijlstra wrote: > On Tue, Feb 12, 2019 at 09:15:13AM +0000, Julien Thierry wrote: > >>>>> diff --git a/kernel/sched/core.c b/kernel/sched/core.c >>>>> index a674c7db..b1bb7e9 100644 >>>>> --- a/kernel/sched/core.c >>>>> +++ b/kernel/sched/core.c >>>>> @@ -3289,6 +3289,14 @@ static inline void schedule_debug(struct task_struct *prev) >>>>> __schedule_bug(prev); >>>>> preempt_count_set(PREEMPT_DISABLED); >>>>> } >>>>> + >>>>> + if (IS_ENABLED(CONFIG_DEBUG_UACCESS_SLEEP) && >>>>> + unlikely(unsafe_user_region_active())) { >>>>> + printk(KERN_ERR "BUG: scheduling while user_access enabled: %s/%d/0x%08x\n", >>>>> + prev->comm, prev->pid, preempt_count()); >>>>> + dump_stack(); >>>>> + } >>>>> + >>>>> rcu_sleep_check(); >>>>> >>>>> profile_hit(SCHED_PROFILING, __builtin_return_address(0)); > >> I guess I'll drop the might_resched() part of this patch if that sounds >> alright. > > I'm still confused by the schedule_debug() part. How is that not broken? Hmmm, I am not exactly sure which part you expect to be broken, I guess it's because of the nature of the uaccess unsafe accessor usage. Basically, the following is a definite no: if (user_access_begin(ptr, size)) { [...] //something that calls schedule [...] user_access_end(); } However the following is fine: - user_access_begin(ptr, size) - taking irq/exception - get preempted - get resumed at some point in time - restore state + eret - user_access_end() That's because exceptions/irq implicitly "suspend" the user access region. (That's what I'm trying to clarify with the comment) So, unsafe_user_region_active() should return false in a irq/exception context. Is this what you were concerned about? Or there still something that might be broken? Thanks, -- Julien Thierry _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel