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=-10.1 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=unavailable 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 4F00DC433E5 for ; Mon, 20 Jul 2020 15:56:33 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 277F5206E9 for ; Mon, 20 Jul 2020 15:56:33 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="I7BgZSnv"; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="HPtNFSpY" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731305AbgGTP4a (ORCPT ); Mon, 20 Jul 2020 11:56:30 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41498 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731741AbgGTP4L (ORCPT ); Mon, 20 Jul 2020 11:56:11 -0400 Received: from galois.linutronix.de (Galois.linutronix.de [IPv6:2a0a:51c0:0:12e:550::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 96802C061794 for ; Mon, 20 Jul 2020 08:56:11 -0700 (PDT) From: "Ahmed S. Darwish" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1595260570; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=csm6qsmcvrkuC3wqo2RObLqWMOC0odk2hhFpp4R4S68=; b=I7BgZSnv43hlG/8MAWSzdbawh2+/ymgU6baklhFOO96spk58wM7RcSneVgAmuDUYHCtf2R QglGd9/4K4BqjrFBBtHBbXbBkOzlBaPp/CbTuk7IaSM+fQxyBsH/X4kEYAfY5DSh1iUhk2 ALJhBpO0xAkbnvoVMjGl9XhdRlBsnXhpJM2lfXDSwQ72WuCepYL2Cdi8rNtCaH5S63bOXG 5zR92mmXyVRxRY3a+ptoQ7W7lMWGnlFYxV5Mq2a2htP4Dl8FjnUPZtJ5hKu43qROnR/OsT l6NBZPfQ4QUDbPVy9EgWffLfNP24ixVctpSNKB/ToFBy1BykMSiKlstTWzP4NQ== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1595260570; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=csm6qsmcvrkuC3wqo2RObLqWMOC0odk2hhFpp4R4S68=; b=HPtNFSpYcYbtURCsvIqNiXS4p9eGFcLbf5SeYCeVrGmrS5umnwW7q/tvdGN3HFOPTaj2/b lLK5SsAsSMdRymCQ== To: Peter Zijlstra , Ingo Molnar , Will Deacon Cc: Thomas Gleixner , "Paul E. McKenney" , "Sebastian A. Siewior" , Steven Rostedt , LKML , "Ahmed S. Darwish" Subject: [PATCH v4 08/24] seqlock: lockdep assert non-preemptibility on seqcount_t write Date: Mon, 20 Jul 2020 17:55:14 +0200 Message-Id: <20200720155530.1173732-9-a.darwish@linutronix.de> In-Reply-To: <20200720155530.1173732-1-a.darwish@linutronix.de> References: <20200519214547.352050-1-a.darwish@linutronix.de> <20200720155530.1173732-1-a.darwish@linutronix.de> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Preemption must be disabled before entering a sequence count write side critical section. Failing to do so, the seqcount read side can preempt the write side section and spin for the entire scheduler tick. If that reader belongs to a real-time scheduling class, it can spin forever and the kernel will livelock. Assert through lockdep that preemption is disabled for seqcount writers. Signed-off-by: Ahmed S. Darwish --- include/linux/seqlock.h | 29 +++++++++++++++++++++++------ 1 file changed, 23 insertions(+), 6 deletions(-) diff --git a/include/linux/seqlock.h b/include/linux/seqlock.h index e885702d8b82..54bc20496392 100644 --- a/include/linux/seqlock.h +++ b/include/linux/seqlock.h @@ -266,6 +266,12 @@ static inline void raw_write_seqcount_end(seqcount_t *s) kcsan_nestable_atomic_end(); } +static inline void __write_seqcount_begin_nested(seqcount_t *s, int subclass) +{ + raw_write_seqcount_begin(s); + seqcount_acquire(&s->dep_map, subclass, 0, _RET_IP_); +} + /** * write_seqcount_begin_nested() - start a seqcount_t write section with * custom lockdep nesting level @@ -276,8 +282,19 @@ static inline void raw_write_seqcount_end(seqcount_t *s) */ static inline void write_seqcount_begin_nested(seqcount_t *s, int subclass) { - raw_write_seqcount_begin(s); - seqcount_acquire(&s->dep_map, subclass, 0, _RET_IP_); + lockdep_assert_preemption_disabled(); + __write_seqcount_begin_nested(s, subclass); +} + +/* + * A write_seqcount_begin() variant w/o lockdep non-preemptibility checks. + * + * Use for internal seqlock.h code where it's known that preemption is + * already disabled. For example, seqlock_t write side functions. + */ +static inline void __write_seqcount_begin(seqcount_t *s) +{ + __write_seqcount_begin_nested(s, 0); } /** @@ -575,7 +592,7 @@ static inline unsigned read_seqretry(const seqlock_t *sl, unsigned start) static inline void write_seqlock(seqlock_t *sl) { spin_lock(&sl->lock); - write_seqcount_begin(&sl->seqcount); + __write_seqcount_begin(&sl->seqcount); } /** @@ -601,7 +618,7 @@ static inline void write_sequnlock(seqlock_t *sl) static inline void write_seqlock_bh(seqlock_t *sl) { spin_lock_bh(&sl->lock); - write_seqcount_begin(&sl->seqcount); + __write_seqcount_begin(&sl->seqcount); } /** @@ -628,7 +645,7 @@ static inline void write_sequnlock_bh(seqlock_t *sl) static inline void write_seqlock_irq(seqlock_t *sl) { spin_lock_irq(&sl->lock); - write_seqcount_begin(&sl->seqcount); + __write_seqcount_begin(&sl->seqcount); } /** @@ -649,7 +666,7 @@ static inline unsigned long __write_seqlock_irqsave(seqlock_t *sl) unsigned long flags; spin_lock_irqsave(&sl->lock, flags); - write_seqcount_begin(&sl->seqcount); + __write_seqcount_begin(&sl->seqcount); return flags; } -- 2.20.1