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=-14.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED 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 BA199C2D0A3 for ; Thu, 29 Oct 2020 10:52:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 5A6DB20731 for ; Thu, 29 Oct 2020 10:52:35 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="PenbXQBW"; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="/06rTWY1" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727342AbgJ2Kwd (ORCPT ); Thu, 29 Oct 2020 06:52:33 -0400 Received: from Galois.linutronix.de ([193.142.43.55]:60776 "EHLO galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727020AbgJ2Kvu (ORCPT ); Thu, 29 Oct 2020 06:51:50 -0400 Date: Thu, 29 Oct 2020 10:51:47 -0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1603968708; h=from:from:sender:sender:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=GKKfJyCsfdpgMfNm5Cc4Iq9qOqaTJCPnr9cIZVoOgfg=; b=PenbXQBW/H14Dh831KDeqsg5GtfyvCsKeDEuUdDvFCrMAri0ZbuEOPi4lH51B74+8rR71f X6h1LiQr+2mhtXNLSr22miPtMUHfLI5Ly/Jk4xebSht/cvOUD+5+/ykoIQ63RZC+b9oWgA 0nVFczlz4kujCCOeB2ZhIkY1HXPp2gDIYQLdK3IhHQ6NZ9/ax+Nj8n0b9csk4RngnbR6wV knPrgd6UXMaT6o1jGIzs/o7oGjOEKbhkvvIkNuzHlYKKyaPTIj1ZODGq0Fd6ZTKET9eT3d 02NH49uBaTOfCuirPIxAcjesvjWDrhYhAxn1gWvAJo4WP6iyiN0FJUyT/j8yIA== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1603968708; h=from:from:sender:sender:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=GKKfJyCsfdpgMfNm5Cc4Iq9qOqaTJCPnr9cIZVoOgfg=; b=/06rTWY1O81lm8iFRdreTlARk5matF3rM3XTHHVVEJU/801CEAjYEuk0kGx31ED7mufhfh IM1MNC2tITNbN3Cw== From: "tip-bot2 for Mathieu Desnoyers" Sender: tip-bot2@linutronix.de Reply-to: linux-kernel@vger.kernel.org To: linux-tip-commits@vger.kernel.org Subject: [tip: sched/core] sched: fix exit_mm vs membarrier (v4) Cc: Mathieu Desnoyers , "Peter Zijlstra (Intel)" , x86 , LKML In-Reply-To: <20201020134715.13909-2-mathieu.desnoyers@efficios.com> References: <20201020134715.13909-2-mathieu.desnoyers@efficios.com> MIME-Version: 1.0 Message-ID: <160396870742.397.11884092890027190780.tip-bot2@tip-bot2> Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The following commit has been merged into the sched/core branch of tip: Commit-ID: 5bc78502322a5e4eef3f1b2a2813751dc6434143 Gitweb: https://git.kernel.org/tip/5bc78502322a5e4eef3f1b2a2813751dc6434143 Author: Mathieu Desnoyers AuthorDate: Tue, 20 Oct 2020 09:47:13 -04:00 Committer: Peter Zijlstra CommitterDate: Thu, 29 Oct 2020 11:00:30 +01:00 sched: fix exit_mm vs membarrier (v4) exit_mm should issue memory barriers after user-space memory accesses, before clearing current->mm, to order user-space memory accesses performed prior to exit_mm before clearing tsk->mm, which has the effect of skipping the membarrier private expedited IPIs. exit_mm should also update the runqueue's membarrier_state so membarrier global expedited IPIs are not sent when they are not needed. The membarrier system call can be issued concurrently with do_exit if we have thread groups created with CLONE_VM but not CLONE_THREAD. Here is the scenario I have in mind: Two thread groups are created, A and B. Thread group B is created by issuing clone from group A with flag CLONE_VM set, but not CLONE_THREAD. Let's assume we have a single thread within each thread group (Thread A and Thread B). The AFAIU we can have: Userspace variables: int x = 0, y = 0; CPU 0 CPU 1 Thread A Thread B (in thread group A) (in thread group B) x = 1 barrier() y = 1 exit() exit_mm() current->mm = NULL; r1 = load y membarrier() skips CPU 0 (no IPI) because its current mm is NULL r2 = load x BUG_ON(r1 == 1 && r2 == 0) Signed-off-by: Mathieu Desnoyers Signed-off-by: Peter Zijlstra (Intel) Link: https://lkml.kernel.org/r/20201020134715.13909-2-mathieu.desnoyers@efficios.com --- include/linux/sched/mm.h | 5 +++++ kernel/exit.c | 16 +++++++++++++++- kernel/sched/membarrier.c | 12 ++++++++++++ 3 files changed, 32 insertions(+), 1 deletion(-) diff --git a/include/linux/sched/mm.h b/include/linux/sched/mm.h index d5ece7a..a91fb3a 100644 --- a/include/linux/sched/mm.h +++ b/include/linux/sched/mm.h @@ -347,6 +347,8 @@ static inline void membarrier_mm_sync_core_before_usermode(struct mm_struct *mm) extern void membarrier_exec_mmap(struct mm_struct *mm); +extern void membarrier_update_current_mm(struct mm_struct *next_mm); + #else #ifdef CONFIG_ARCH_HAS_MEMBARRIER_CALLBACKS static inline void membarrier_arch_switch_mm(struct mm_struct *prev, @@ -361,6 +363,9 @@ static inline void membarrier_exec_mmap(struct mm_struct *mm) static inline void membarrier_mm_sync_core_before_usermode(struct mm_struct *mm) { } +static inline void membarrier_update_current_mm(struct mm_struct *next_mm) +{ +} #endif #endif /* _LINUX_SCHED_MM_H */ diff --git a/kernel/exit.c b/kernel/exit.c index 87a2d51..a3dd6b3 100644 --- a/kernel/exit.c +++ b/kernel/exit.c @@ -475,10 +475,24 @@ static void exit_mm(void) BUG_ON(mm != current->active_mm); /* more a memory barrier than a real lock */ task_lock(current); + /* + * When a thread stops operating on an address space, the loop + * in membarrier_private_expedited() may not observe that + * tsk->mm, and the loop in membarrier_global_expedited() may + * not observe a MEMBARRIER_STATE_GLOBAL_EXPEDITED + * rq->membarrier_state, so those would not issue an IPI. + * Membarrier requires a memory barrier after accessing + * user-space memory, before clearing tsk->mm or the + * rq->membarrier_state. + */ + smp_mb__after_spinlock(); + local_irq_disable(); current->mm = NULL; - mmap_read_unlock(mm); + membarrier_update_current_mm(NULL); enter_lazy_tlb(mm, current); + local_irq_enable(); task_unlock(current); + mmap_read_unlock(mm); mm_update_next_owner(mm); mmput(mm); if (test_thread_flag(TIF_MEMDIE)) diff --git a/kernel/sched/membarrier.c b/kernel/sched/membarrier.c index e23e74d..aac3292 100644 --- a/kernel/sched/membarrier.c +++ b/kernel/sched/membarrier.c @@ -76,6 +76,18 @@ void membarrier_exec_mmap(struct mm_struct *mm) this_cpu_write(runqueues.membarrier_state, 0); } +void membarrier_update_current_mm(struct mm_struct *next_mm) +{ + struct rq *rq = this_rq(); + int membarrier_state = 0; + + if (next_mm) + membarrier_state = atomic_read(&next_mm->membarrier_state); + if (READ_ONCE(rq->membarrier_state) == membarrier_state) + return; + WRITE_ONCE(rq->membarrier_state, membarrier_state); +} + static int membarrier_global_expedited(void) { int cpu;