From patchwork Wed Jun 3 14:49:48 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Ahmed S. Darwish" X-Patchwork-Id: 11585793 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 6402592A for ; Wed, 3 Jun 2020 14:50:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 5558620772 for ; Wed, 3 Jun 2020 14:50:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726385AbgFCOup (ORCPT ); Wed, 3 Jun 2020 10:50:45 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59720 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726462AbgFCOuX (ORCPT ); Wed, 3 Jun 2020 10:50:23 -0400 Received: from Galois.linutronix.de (Galois.linutronix.de [IPv6:2a0a:51c0:0:12e:550::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id F0772C08C5C1; Wed, 3 Jun 2020 07:50:22 -0700 (PDT) Received: from [5.158.153.53] (helo=debian-buster-darwi.lab.linutronix.de.) by Galois.linutronix.de with esmtpsa (TLS1.2:DHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.80) (envelope-from ) id 1jgUie-0001zr-3o; Wed, 03 Jun 2020 16:50:16 +0200 From: "Ahmed S. Darwish" To: Peter Zijlstra , Ingo Molnar , Will Deacon Cc: Thomas Gleixner , "Paul E. McKenney" , "Sebastian A. Siewior" , Steven Rostedt , LKML , "Ahmed S. Darwish" , Jens Axboe , Vivek Goyal , linux-block@vger.kernel.org Subject: [PATCH v2 5/6] block: nr_sects_write(): Disable preemption on seqcount write Date: Wed, 3 Jun 2020 16:49:48 +0200 Message-Id: <20200603144949.1122421-6-a.darwish@linutronix.de> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20200603144949.1122421-1-a.darwish@linutronix.de> References: <20200603144949.1122421-1-a.darwish@linutronix.de> MIME-Version: 1.0 X-Linutronix-Spam-Score: -1.0 X-Linutronix-Spam-Level: - X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required, ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001 Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org For optimized block readers not holding a mutex, the "number of sectors" 64-bit value is protected from tearing on 32-bit architectures by a sequence counter. Disable preemption before entering that sequence counter's write side critical section. Otherwise, the read side can preempt the write side section and spin for the entire scheduler tick. If the reader belongs to a real-time scheduling class, it can spin forever and the kernel will livelock. Fixes: c83f6bf98dc1 ("block: add partition resize function to blkpg ioctl") Cc: Signed-off-by: Ahmed S. Darwish Reviewed-by: Sebastian Andrzej Siewior --- block/blk.h | 2 ++ 1 file changed, 2 insertions(+) diff --git a/block/blk.h b/block/blk.h index 0a94ec68af32..151f86932547 100644 --- a/block/blk.h +++ b/block/blk.h @@ -470,9 +470,11 @@ static inline sector_t part_nr_sects_read(struct hd_struct *part) static inline void part_nr_sects_write(struct hd_struct *part, sector_t size) { #if BITS_PER_LONG==32 && defined(CONFIG_SMP) + preempt_disable(); write_seqcount_begin(&part->nr_sects_seq); part->nr_sects = size; write_seqcount_end(&part->nr_sects_seq); + preempt_enable(); #elif BITS_PER_LONG==32 && defined(CONFIG_PREEMPTION) preempt_disable(); part->nr_sects = size;