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=-10.0 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT 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 B7B15C433E0 for ; Tue, 23 Jun 2020 20:33:48 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8A1F32098B for ; Tue, 23 Jun 2020 20:33:48 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1592944428; bh=sSWelBKzhntvZvh7CNi1kL0bBAXPsuvV7Ivr7aGUKTA=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=jHkXN/NGIprHsyIiO0h+aktKBA8aM7eh36xS+AonJQdLoLpxLFmiFzM/R7EeQI7u7 c6XdE2hZpeiUGTU7lkR8Z6GAslSdvmhldRuHgg5iABUAC1vRwKC2GfxusbzF+1p+pc PkTY9WXYEJK5F3xsnKCj3Q/vFc42js9+fgxhW9sc= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2391451AbgFWUdq (ORCPT ); Tue, 23 Jun 2020 16:33:46 -0400 Received: from mail.kernel.org ([198.145.29.99]:54846 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2391424AbgFWUd3 (ORCPT ); Tue, 23 Jun 2020 16:33:29 -0400 Received: from localhost (83-86-89-107.cable.dynamic.v4.ziggo.nl [83.86.89.107]) (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 A2BAE206C3; Tue, 23 Jun 2020 20:33:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1592944409; bh=sSWelBKzhntvZvh7CNi1kL0bBAXPsuvV7Ivr7aGUKTA=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=MpbSp/dRlwS7z/zmFFO96ETWGg8fZEQmWQzwhfYzwy6wkDhyYjQghYwIkLETmCqb8 KmDEBpLs6UG/6mHMKEzeqArcUknyLy6U3PcDhxx/4BsG9zJH1H6NT+zHvrI3VkY/a/ 8Qpchl8yh+zUGATz5KUl/QlkC3M88QNx268+MH+g= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, "Ahmed S. Darwish" , Sebastian Andrzej Siewior , Jens Axboe , Sasha Levin Subject: [PATCH 5.4 292/314] block: nr_sects_write(): Disable preemption on seqcount write Date: Tue, 23 Jun 2020 21:58:07 +0200 Message-Id: <20200623195352.902010609@linuxfoundation.org> X-Mailer: git-send-email 2.27.0 In-Reply-To: <20200623195338.770401005@linuxfoundation.org> References: <20200623195338.770401005@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Ahmed S. Darwish [ Upstream commit 15b81ce5abdc4b502aa31dff2d415b79d2349d2f ] 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 Signed-off-by: Jens Axboe Signed-off-by: Sasha Levin --- include/linux/genhd.h | 2 ++ 1 file changed, 2 insertions(+) diff --git a/include/linux/genhd.h b/include/linux/genhd.h index 8b5330dd5ac09..62a2ec9f17df8 100644 --- a/include/linux/genhd.h +++ b/include/linux/genhd.h @@ -750,9 +750,11 @@ 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_PREEMPT) preempt_disable(); part->nr_sects = size; -- 2.25.1