Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751189AbWCKQAp (ORCPT ); Sat, 11 Mar 2006 11:00:45 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751192AbWCKQAp (ORCPT ); Sat, 11 Mar 2006 11:00:45 -0500 Received: from mail.parknet.jp ([210.171.160.80]:27151 "EHLO parknet.jp") by vger.kernel.org with ESMTP id S1751189AbWCKQAp (ORCPT ); Sat, 11 Mar 2006 11:00:45 -0500 X-AuthUser: hirofumi@parknet.jp To: linux-kernel@vger.kernel.org Cc: Andrew Morton Subject: [PATCH] Fix a race condition between ->i_mapping and iput() From: OGAWA Hirofumi Date: Sun, 12 Mar 2006 01:00:22 +0900 Message-ID: <87hd65geeh.fsf@duaron.myhome.or.jp> User-Agent: Gnus/5.11 (Gnus v5.11) Emacs/22.0.50 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3611 Lines: 112 This race became a cause of oops, and can reproduce by the following. while true; do dd if=/dev/zero of=/dev/.static/dev/hdg1 bs=512 count=1000 & sync done This race condition was between __sync_single_inode() and iput(). cpu0 (fs's inode) cpu1 (bdev's inode) ------------------------------------------------------------------------ close("/dev/hda2") [...] __sync_single_inode() /* copy the bdev's ->i_mapping */ mapping = inode->i_mapping; generic_forget_inode() bdev_clear_inode() /* restre the fs's ->i_mapping */ inode->i_mapping = &inode->i_data; /* bdev's inode was freed */ destroy_inode(inode); if (wait) { /* dereference a freed bdev's mapping->host */ filemap_fdatawait(mapping); /* Oops */ Since __sync_signle_inode() is only taking a ref-count of fs's inode, the another process can be close() and freeing the bdev's inode while writing fs's inode. So, __sync_signle_inode() accesses the freed ->i_mapping, oops. This patch takes ref-count of bdev's inode for fs's inode before setting a ->i_mapping, and the clear_inode() of fs's inode does iput(). So, if fs's inode is still living, bdev's inode shouldn't be freed. This lifetime rule may be a poor, but very simple. Signed-off-by: OGAWA Hirofumi --- fs/block_dev.c | 32 +++++++++++++++++++++++++------- 1 file changed, 25 insertions(+), 7 deletions(-) diff -puN fs/block_dev.c~i_mapping-race-fix-2 fs/block_dev.c --- linux-2.6/fs/block_dev.c~i_mapping-race-fix-2 2006-03-11 16:19:07.000000000 +0900 +++ linux-2.6-hirofumi/fs/block_dev.c 2006-03-11 17:52:11.000000000 +0900 @@ -418,21 +418,31 @@ EXPORT_SYMBOL(bdput); static struct block_device *bd_acquire(struct inode *inode) { struct block_device *bdev; + spin_lock(&bdev_lock); bdev = inode->i_bdev; - if (bdev && igrab(bdev->bd_inode)) { + if (bdev) { + atomic_inc(&bdev->bd_inode->i_count); spin_unlock(&bdev_lock); return bdev; } spin_unlock(&bdev_lock); + bdev = bdget(inode->i_rdev); if (bdev) { spin_lock(&bdev_lock); - if (inode->i_bdev) - __bd_forget(inode); - inode->i_bdev = bdev; - inode->i_mapping = bdev->bd_inode->i_mapping; - list_add(&inode->i_devices, &bdev->bd_inodes); + if (!inode->i_bdev) { + /* + * We take an additional bd_inode->i_count for inode, + * and it's released in clear_inode() of inode. + * So, we can access it via ->i_mapping always + * without igrab(). + */ + atomic_inc(&bdev->bd_inode->i_count); + inode->i_bdev = bdev; + inode->i_mapping = bdev->bd_inode->i_mapping; + list_add(&inode->i_devices, &bdev->bd_inodes); + } spin_unlock(&bdev_lock); } return bdev; @@ -442,10 +452,18 @@ static struct block_device *bd_acquire(s void bd_forget(struct inode *inode) { + struct block_device *bdev = NULL; + spin_lock(&bdev_lock); - if (inode->i_bdev) + if (inode->i_bdev) { + if (inode->i_sb != blockdev_superblock) + bdev = inode->i_bdev; __bd_forget(inode); + } spin_unlock(&bdev_lock); + + if (bdev) + iput(bdev->bd_inode); } int bd_claim(struct block_device *bdev, void *holder) _ - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/