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=-9.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, 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 603F3C4BA10 for ; Wed, 26 Feb 2020 11:11:54 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 36F1C24691 for ; Wed, 26 Feb 2020 11:11:54 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728087AbgBZLLx (ORCPT ); Wed, 26 Feb 2020 06:11:53 -0500 Received: from szxga07-in.huawei.com ([45.249.212.35]:38476 "EHLO huawei.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1728047AbgBZLLw (ORCPT ); Wed, 26 Feb 2020 06:11:52 -0500 Received: from DGGEMS402-HUB.china.huawei.com (unknown [172.30.72.58]) by Forcepoint Email with ESMTP id 870352894852E0BADC16; Wed, 26 Feb 2020 19:11:45 +0800 (CST) Received: from huawei.com (10.90.53.225) by DGGEMS402-HUB.china.huawei.com (10.3.19.202) with Microsoft SMTP Server id 14.3.439.0; Wed, 26 Feb 2020 19:11:40 +0800 From: Yufen Yu To: , , CC: , , , Subject: [PATCH v2 3/7] bdi: protect device lifetime with RCU Date: Wed, 26 Feb 2020 19:18:47 +0800 Message-ID: <20200226111851.55348-4-yuyufen@huawei.com> X-Mailer: git-send-email 2.16.2.dirty In-Reply-To: <20200226111851.55348-1-yuyufen@huawei.com> References: <20200226111851.55348-1-yuyufen@huawei.com> MIME-Version: 1.0 Content-Type: text/plain X-Originating-IP: [10.90.53.225] X-CFilter-Loop: Reflected Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org We reported a kernel crash: [201962.639350] Call trace: [201962.644403] string+0x28/0xa0 [201962.650501] vsnprintf+0x5f0/0x748 [201962.657472] seq_vprintf+0x70/0x98 [201962.664442] seq_printf+0x7c/0xa0 [201962.671238] __blkg_prfill_rwstat+0x84/0x128 [201962.679949] blkg_prfill_rwstat_field+0x94/0xc0 [201962.689182] blkcg_print_blkgs+0xcc/0x140 [201962.697370] blkg_print_stat_bytes+0x4c/0x60 [201962.706083] cgroup_seqfile_show+0x58/0xc0 [201962.714446] kernfs_seq_show+0x44/0x50 [201962.722112] seq_read+0xd4/0x4a8 [201962.728732] kernfs_fop_read+0x16c/0x218 [201962.736748] __vfs_read+0x60/0x188 [201962.743717] vfs_read+0x94/0x150 [201962.750338] ksys_read+0x6c/0xd8 [201962.756958] __arm64_sys_read+0x24/0x30 [201962.764800] el0_svc_common+0x78/0x130 [201962.772466] el0_svc_handler+0x38/0x78 [201962.780131] el0_svc+0x8/0xc __blkg_prfill_rwstat() tries to get the device name by 'bdi->dev', while the device and kobj->name has been freed by bdi_unregister(). Then, blkg_dev_name() will return an invalid name pointer, resulting in crash on string(). The race as following: CPU1 CPU2 blkg_print_stat_bytes __scsi_remove_device del_gendisk bdi_unregister put_device(bdi->dev) kfree(bdi->dev) __blkg_prfill_rwstat blkg_dev_name //use the freed bdi->dev dev_name(blkg->q->backing_dev_info->dev) bdi->dev = NULL We fix the bug by protecting the device lifetime with RCU. call_rcu() will free the device until all of the readers complete. Since both of blkg_dev_name() and device name have been protected by rcu_read_lock/unlock(). Thus, we don't need to do it again. Just use rcu_dereference() to fetch rcu_dev here. Signed-off-by: Yufen Yu --- block/bfq-iosched.c | 2 +- block/blk-cgroup.c | 8 ++++-- block/genhd.c | 4 +-- fs/ext4/super.c | 2 +- include/linux/backing-dev-defs.h | 8 +++++- include/linux/backing-dev.h | 4 +-- mm/backing-dev.c | 59 +++++++++++++++++++++++++++++++++------- 7 files changed, 68 insertions(+), 19 deletions(-) diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c index 8c436abfaf14..00904611b8e4 100644 --- a/block/bfq-iosched.c +++ b/block/bfq-iosched.c @@ -4978,7 +4978,7 @@ bfq_set_next_ioprio_data(struct bfq_queue *bfqq, struct bfq_io_cq *bic) ioprio_class = IOPRIO_PRIO_CLASS(bic->ioprio); switch (ioprio_class) { default: - dev_err(bfqq->bfqd->queue->backing_dev_info->dev, + dev_err(&bfqq->bfqd->queue->backing_dev_info->rcu_dev->dev, "bfq: bad prio class %d\n", ioprio_class); /* fall through */ case IOPRIO_CLASS_NONE: diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c index a229b94d5390..7ab1af3925c5 100644 --- a/block/blk-cgroup.c +++ b/block/blk-cgroup.c @@ -494,9 +494,13 @@ static int blkcg_reset_stats(struct cgroup_subsys_state *css, const char *blkg_dev_name(struct blkcg_gq *blkg) { + struct bdi_rcu_device *rcu_dev; + + rcu_dev = rcu_dereference(blkg->q->backing_dev_info->rcu_dev); + /* some drivers (floppy) instantiate a queue w/o disk registered */ - if (blkg->q->backing_dev_info->dev) - return dev_name(blkg->q->backing_dev_info->dev); + if (rcu_dev) + return dev_name(&rcu_dev->dev); return NULL; } diff --git a/block/genhd.c b/block/genhd.c index ff6268970ddc..bd406b0fb471 100644 --- a/block/genhd.c +++ b/block/genhd.c @@ -668,9 +668,9 @@ static void register_disk(struct device *parent, struct gendisk *disk, kobject_uevent(&part_to_dev(part)->kobj, KOBJ_ADD); disk_part_iter_exit(&piter); - if (disk->queue->backing_dev_info->dev) { + if (disk->queue->backing_dev_info->rcu_dev) { err = sysfs_create_link(&ddev->kobj, - &disk->queue->backing_dev_info->dev->kobj, + &disk->queue->backing_dev_info->rcu_dev->dev.kobj, "bdi"); WARN_ON(err); } diff --git a/fs/ext4/super.c b/fs/ext4/super.c index ff1b764b0c0e..7781773f9f77 100644 --- a/fs/ext4/super.c +++ b/fs/ext4/super.c @@ -388,7 +388,7 @@ static int block_device_ejected(struct super_block *sb) struct inode *bd_inode = sb->s_bdev->bd_inode; struct backing_dev_info *bdi = inode_to_bdi(bd_inode); - return bdi->dev == NULL; + return bdi->rcu_dev == NULL; } static void ext4_journal_commit_callback(journal_t *journal, transaction_t *txn) diff --git a/include/linux/backing-dev-defs.h b/include/linux/backing-dev-defs.h index 4fc87dee005a..3d2294c428c1 100644 --- a/include/linux/backing-dev-defs.h +++ b/include/linux/backing-dev-defs.h @@ -13,6 +13,7 @@ #include #include #include +#include struct page; struct device; @@ -185,6 +186,11 @@ struct bdi_writeback { #endif }; +struct bdi_rcu_device { + struct device dev; + struct rcu_head rcu_head; +}; + struct backing_dev_info { u64 id; struct rb_node rb_node; /* keyed by ->id */ @@ -219,7 +225,7 @@ struct backing_dev_info { #endif wait_queue_head_t wb_waitq; - struct device *dev; + struct bdi_rcu_device *rcu_dev; struct device *owner; struct timer_list laptop_mode_wb_timer; diff --git a/include/linux/backing-dev.h b/include/linux/backing-dev.h index f88197c1ffc2..67e429b203a1 100644 --- a/include/linux/backing-dev.h +++ b/include/linux/backing-dev.h @@ -509,9 +509,9 @@ extern const char *bdi_unknown_name; static inline const char *bdi_dev_name(struct backing_dev_info *bdi) { - if (!bdi || !bdi->dev) + if (!bdi || !bdi->rcu_dev) return bdi_unknown_name; - return dev_name(bdi->dev); + return dev_name(&bdi->rcu_dev->dev); } #endif /* _LINUX_BACKING_DEV_H */ diff --git a/mm/backing-dev.c b/mm/backing-dev.c index 62f05f605fb5..b29c0ad43477 100644 --- a/mm/backing-dev.c +++ b/mm/backing-dev.c @@ -850,7 +850,7 @@ static int bdi_init(struct backing_dev_info *bdi) { int ret; - bdi->dev = NULL; + bdi->rcu_dev = NULL; kref_init(&bdi->refcnt); bdi->min_ratio = 0; @@ -930,20 +930,44 @@ struct backing_dev_info *bdi_get_by_id(u64 id) return bdi; } +static void bdi_device_release(struct device *dev) +{ + struct bdi_rcu_device *rcu_dev = container_of(dev, + struct bdi_rcu_device, dev); + kfree(rcu_dev); +} + int bdi_register_va(struct backing_dev_info *bdi, const char *fmt, va_list args) { struct device *dev; struct rb_node *parent, **p; + struct bdi_rcu_device *rcu_dev; + int retval = -ENODEV; - if (bdi->dev) /* The driver needs to use separate queues per device */ + /* The driver needs to use separate queues per device */ + if (bdi->rcu_dev) return 0; - dev = device_create_vargs(bdi_class, NULL, MKDEV(0, 0), bdi, fmt, args); - if (IS_ERR(dev)) - return PTR_ERR(dev); + rcu_dev = kzalloc(sizeof(struct bdi_rcu_device), GFP_KERNEL); + if (!rcu_dev) + return -ENOMEM; + + /* initialize device */ + dev = &rcu_dev->dev; + device_initialize(dev); + dev->class = bdi_class; + dev->release = bdi_device_release; + dev_set_drvdata(dev, (void *)bdi); + retval = kobject_set_name_vargs(&dev->kobj, fmt, args); + if (retval) + goto error; + + retval = device_add(dev); + if (retval) + goto error; cgwb_bdi_register(bdi); - bdi->dev = dev; + bdi->rcu_dev = rcu_dev; bdi_debug_register(bdi, dev_name(dev)); set_bit(WB_registered, &bdi->wb.state); @@ -962,6 +986,10 @@ int bdi_register_va(struct backing_dev_info *bdi, const char *fmt, va_list args) trace_writeback_bdi_register(bdi); return 0; + +error: + put_device(&rcu_dev->dev); + return retval; } EXPORT_SYMBOL(bdi_register_va); @@ -1005,17 +1033,28 @@ static void bdi_remove_from_list(struct backing_dev_info *bdi) synchronize_rcu_expedited(); } +static void bdi_put_device_rcu(struct rcu_head *rcu) +{ + struct bdi_rcu_device *rcu_dev = container_of(rcu, + struct bdi_rcu_device, rcu_head); + put_device(&rcu_dev->dev); +} + void bdi_unregister(struct backing_dev_info *bdi) { + struct bdi_rcu_device *rcu_dev = bdi->rcu_dev; + /* make sure nobody finds us on the bdi_list anymore */ bdi_remove_from_list(bdi); wb_shutdown(&bdi->wb); cgwb_bdi_unregister(bdi); - if (bdi->dev) { + if (rcu_dev) { bdi_debug_unregister(bdi); - device_unregister(bdi->dev); - bdi->dev = NULL; + get_device(&rcu_dev->dev); + device_unregister(&rcu_dev->dev); + rcu_assign_pointer(bdi->rcu_dev, NULL); + call_rcu(&rcu_dev->rcu_head, bdi_put_device_rcu); } if (bdi->owner) { @@ -1031,7 +1070,7 @@ static void release_bdi(struct kref *ref) if (test_bit(WB_registered, &bdi->wb.state)) bdi_unregister(bdi); - WARN_ON_ONCE(bdi->dev); + WARN_ON_ONCE(bdi->rcu_dev); wb_exit(&bdi->wb); cgwb_bdi_exit(bdi); kfree(bdi); -- 2.16.2.dirty