4.16-stable review patch. If anyone has any objections, please let me know.
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From: Nikolay Borisov nborisov@suse.com
commit fe816d0f1d4c31c4c31d42ca78a87660565fc800 upstream.
When a transaction is aborted btrfs_cleanup_transaction is called to cleanup all the various in-flight bits and pieces which migth be active. One of those is delalloc inodes - inodes which have dirty pages which haven't been persisted yet. Currently the process of freeing such delalloc inodes in exceptional circumstances such as transaction abort boiled down to calling btrfs_invalidate_inodes whose sole job is to invalidate the dentries for all inodes related to a root. This is in fact wrong and insufficient since such delalloc inodes will likely have pending pages or ordered-extents and will be linked to the sb->s_inode_list. This means that unmounting a btrfs instance with an aborted transaction could potentially lead inodes/their pages visible to the system long after their superblock has been freed. This in turn leads to a "use-after-free" situation once page shrink is triggered. This situation could be simulated by running generic/019 which would cause such inodes to be left hanging, followed by generic/176 which causes memory pressure and page eviction which lead to touching the freed super block instance. This situation is additionally detected by the unmount code of VFS with the following message:
"VFS: Busy inodes after unmount of Self-destruct in 5 seconds. Have a nice day..."
Additionally btrfs hits WARN_ON(!RB_EMPTY_ROOT(&root->inode_tree)); in free_fs_root for the same reason.
This patch aims to rectify the sitaution by doing the following:
1. Change btrfs_destroy_delalloc_inodes so that it calls invalidate_inode_pages2 for every inode on the delalloc list, this ensures that all the pages of the inode are released. This function boils down to calling btrfs_releasepage. During test I observed cases where inodes on the delalloc list were having an i_count of 0, so this necessitates using igrab to be sure we are working on a non-freed inode.
2. Since calling btrfs_releasepage might queue delayed iputs move the call out to btrfs_cleanup_transaction in btrfs_error_commit_super before calling run_delayed_iputs for the last time. This is necessary to ensure that delayed iputs are run.
Note: this patch is tagged for 4.14 stable but the fix applies to older versions too but needs to be backported manually due to conflicts.
CC: stable@vger.kernel.org # 4.14.x: 2b8773313494: btrfs: Split btrfs_del_delalloc_inode into 2 functions CC: stable@vger.kernel.org # 4.14.x Signed-off-by: Nikolay Borisov nborisov@suse.com Reviewed-by: David Sterba dsterba@suse.com [ add comment to igrab ] Signed-off-by: David Sterba dsterba@suse.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- fs/btrfs/disk-io.c | 26 +++++++++++++++----------- 1 file changed, 15 insertions(+), 11 deletions(-)
--- a/fs/btrfs/disk-io.c +++ b/fs/btrfs/disk-io.c @@ -3744,6 +3744,7 @@ void close_ctree(struct btrfs_fs_info *f set_bit(BTRFS_FS_CLOSING_DONE, &fs_info->flags);
btrfs_free_qgroup_config(fs_info); + ASSERT(list_empty(&fs_info->delalloc_roots));
if (percpu_counter_sum(&fs_info->delalloc_bytes)) { btrfs_info(fs_info, "at unmount delalloc count %lld", @@ -4049,15 +4050,15 @@ static int btrfs_check_super_valid(struc
static void btrfs_error_commit_super(struct btrfs_fs_info *fs_info) { + /* cleanup FS via transaction */ + btrfs_cleanup_transaction(fs_info); + mutex_lock(&fs_info->cleaner_mutex); btrfs_run_delayed_iputs(fs_info); mutex_unlock(&fs_info->cleaner_mutex);
down_write(&fs_info->cleanup_work_sem); up_write(&fs_info->cleanup_work_sem); - - /* cleanup FS via transaction */ - btrfs_cleanup_transaction(fs_info); }
static void btrfs_destroy_ordered_extents(struct btrfs_root *root) @@ -4182,19 +4183,23 @@ static void btrfs_destroy_delalloc_inode list_splice_init(&root->delalloc_inodes, &splice);
while (!list_empty(&splice)) { + struct inode *inode = NULL; btrfs_inode = list_first_entry(&splice, struct btrfs_inode, delalloc_inodes); - - list_del_init(&btrfs_inode->delalloc_inodes); - clear_bit(BTRFS_INODE_IN_DELALLOC_LIST, - &btrfs_inode->runtime_flags); + __btrfs_del_delalloc_inode(root, btrfs_inode); spin_unlock(&root->delalloc_lock);
- btrfs_invalidate_inodes(btrfs_inode->root); - + /* + * Make sure we get a live inode and that it'll not disappear + * meanwhile. + */ + inode = igrab(&btrfs_inode->vfs_inode); + if (inode) { + invalidate_inode_pages2(inode->i_mapping); + iput(inode); + } spin_lock(&root->delalloc_lock); } - spin_unlock(&root->delalloc_lock); }
@@ -4210,7 +4215,6 @@ static void btrfs_destroy_all_delalloc_i while (!list_empty(&splice)) { root = list_first_entry(&splice, struct btrfs_root, delalloc_root); - list_del_init(&root->delalloc_root); root = btrfs_grab_fs_root(root); BUG_ON(!root); spin_unlock(&fs_info->delalloc_root_lock);