From patchwork Tue Jan 31 12:54:29 2017 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Jan Kara X-Patchwork-Id: 9547197 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork.web.codeaurora.org (Postfix) with ESMTP id 45415604DF for ; Tue, 31 Jan 2017 13:14:38 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 37D1D27F9E for ; Tue, 31 Jan 2017 13:14:38 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 2CB702832B; Tue, 31 Jan 2017 13:14:38 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.9 required=2.0 tests=BAYES_00,RCVD_IN_DNSWL_HI autolearn=ham version=3.3.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 9D09827F9E for ; Tue, 31 Jan 2017 13:14:37 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752159AbdAaNOV (ORCPT ); Tue, 31 Jan 2017 08:14:21 -0500 Received: from mx2.suse.de ([195.135.220.15]:58102 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752012AbdAaNNw (ORCPT ); Tue, 31 Jan 2017 08:13:52 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (charybdis-ext.suse.de [195.135.220.254]) by mx2.suse.de (Postfix) with ESMTP id 9EDA3ABEA; Tue, 31 Jan 2017 12:54:38 +0000 (UTC) Received: by quack2.suse.cz (Postfix, from userid 1000) id 26C301E1126; Tue, 31 Jan 2017 13:54:37 +0100 (CET) From: Jan Kara To: Jens Axboe Cc: linux-block@vger.kernel.org, Christoph Hellwig , Dan Williams , Thiago Jung Bauermann , Laurent Dufour , Jan Kara Subject: [PATCH 4/4] block: Make blk_get_backing_dev_info() safe without open bdev Date: Tue, 31 Jan 2017 13:54:29 +0100 Message-Id: <20170131125429.14303-5-jack@suse.cz> X-Mailer: git-send-email 2.10.2 In-Reply-To: <20170131125429.14303-1-jack@suse.cz> References: <20170131125429.14303-1-jack@suse.cz> Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP Currenly blk_get_backing_dev_info() is not safe to be called when the block device is not open as bdev->bd_disk is NULL in that case. However inode_to_bdi() uses this function and may be call called from flusher worker or other writeback related functions without bdev being open which leads to crashes such as: [113031.075540] Unable to handle kernel paging request for data at address 0x00000000 [113031.075614] Faulting instruction address: 0xc0000000003692e0 0:mon> t [c0000000fb65f900] c00000000036cb6c writeback_sb_inodes+0x30c/0x590 [c0000000fb65fa10] c00000000036ced4 __writeback_inodes_wb+0xe4/0x150 [c0000000fb65fa70] c00000000036d33c wb_writeback+0x30c/0x450 [c0000000fb65fb40] c00000000036e198 wb_workfn+0x268/0x580 [c0000000fb65fc50] c0000000000f3470 process_one_work+0x1e0/0x590 [c0000000fb65fce0] c0000000000f38c8 worker_thread+0xa8/0x660 [c0000000fb65fd80] c0000000000fc4b0 kthread+0x110/0x130 [c0000000fb65fe30] c0000000000098f0 ret_from_kernel_thread+0x5c/0x6c --- Exception: 0 at 0000000000000000 0:mon> e cpu 0x0: Vector: 300 (Data Access) at [c0000000fb65f620] pc: c0000000003692e0: locked_inode_to_wb_and_lock_list+0x50/0x290 lr: c00000000036cb6c: writeback_sb_inodes+0x30c/0x590 sp: c0000000fb65f8a0 msr: 800000010280b033 dar: 0 dsisr: 40000000 current = 0xc0000001d69be400 paca = 0xc000000003480000 softe: 0 irq_happened: 0x01 pid = 18689, comm = kworker/u16:10 Fix the problem by grabbing reference to bdi on first open of the block device and drop the reference only once the inode is evicted from memory. This pins struct backing_dev_info in memory and thus fixes the crashes. Reported-by: Dan Williams Reported-by: Laurent Dufour Signed-off-by: Jan Kara Reviewed-by: Christoph Hellwig Tested-by: Dan Williams --- block/blk-core.c | 8 +++----- fs/block_dev.c | 7 +++++++ include/linux/fs.h | 1 + 3 files changed, 11 insertions(+), 5 deletions(-) diff --git a/block/blk-core.c b/block/blk-core.c index 545ccb4b96f3..84fabb51714a 100644 --- a/block/blk-core.c +++ b/block/blk-core.c @@ -109,14 +109,12 @@ void blk_queue_congestion_threshold(struct request_queue *q) * @bdev: device * * Locates the passed device's request queue and returns the address of its - * backing_dev_info. This function can only be called if @bdev is opened - * and the return value is never NULL. + * backing_dev_info. The return value is never NULL however we may return + * &noop_backing_dev_info if the bdev is not currently open. */ struct backing_dev_info *blk_get_backing_dev_info(struct block_device *bdev) { - struct request_queue *q = bdev_get_queue(bdev); - - return q->backing_dev_info; + return bdev->bd_bdi; } EXPORT_SYMBOL(blk_get_backing_dev_info); diff --git a/fs/block_dev.c b/fs/block_dev.c index ed6a34be7a1e..601b71b76d7f 100644 --- a/fs/block_dev.c +++ b/fs/block_dev.c @@ -884,6 +884,8 @@ static void bdev_evict_inode(struct inode *inode) spin_lock(&bdev_lock); list_del_init(&bdev->bd_list); spin_unlock(&bdev_lock); + if (bdev->bd_bdi != &noop_backing_dev_info) + bdi_put(bdev->bd_bdi); } static const struct super_operations bdev_sops = { @@ -986,6 +988,7 @@ struct block_device *bdget(dev_t dev) bdev->bd_contains = NULL; bdev->bd_super = NULL; bdev->bd_inode = inode; + bdev->bd_bdi = &noop_backing_dev_info; bdev->bd_block_size = (1 << inode->i_blkbits); bdev->bd_part_count = 0; bdev->bd_invalidated = 0; @@ -1542,6 +1545,8 @@ static int __blkdev_get(struct block_device *bdev, fmode_t mode, int for_part) bdev->bd_disk = disk; bdev->bd_queue = disk->queue; bdev->bd_contains = bdev; + if (bdev->bd_bdi == &noop_backing_dev_info) + bdev->bd_bdi = bdi_get(disk->queue->backing_dev_info); if (!partno) { ret = -ENXIO; @@ -1637,6 +1642,8 @@ static int __blkdev_get(struct block_device *bdev, fmode_t mode, int for_part) bdev->bd_disk = NULL; bdev->bd_part = NULL; bdev->bd_queue = NULL; + bdi_put(bdev->bd_bdi); + bdev->bd_bdi = &noop_backing_dev_info; if (bdev != bdev->bd_contains) __blkdev_put(bdev->bd_contains, mode, 1); bdev->bd_contains = NULL; diff --git a/include/linux/fs.h b/include/linux/fs.h index 702cb6c50194..c930cbc19342 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -423,6 +423,7 @@ struct block_device { int bd_invalidated; struct gendisk * bd_disk; struct request_queue * bd_queue; + struct backing_dev_info *bd_bdi; struct list_head bd_list; /* * Private data. You must have bd_claim'ed the block_device