@@ -115,10 +115,14 @@ static int compression_compress_pages(int type, struct list_head *ws,
case BTRFS_COMPRESS_NONE:
default:
/*
- * This can't happen, the type is validated several times
- * before we get here. As a sane fallback, return what the
- * callers will understand as 'no compression happened'.
+ * This happens when compression races with remount to no
+ * compress, while caller doesn't call inode_need_compress()
+ * to check if we really need to compress.
+ *
+ * Not a big deal, just need to inform caller that we
+ * haven't allocated any pages yet.
*/
+ *out_pages = 0;
return -E2BIG;
}
}
[BUG] With next-20200731 tag (079ad2fb4bf9eba8a0aaab014b49705cd7f07c66), unmounting a btrfs with quota disabled will cause the following NULL pointer dereference: BTRFS info (device dm-5): has skinny extents BUG: kernel NULL pointer dereference, address: 0000000000000018 #PF: supervisor read access in kernel mode #PF: error_code(0x0000) - not-present page CPU: 7 PID: 637 Comm: umount Not tainted 5.8.0-rc7-next-20200731-custom #76 RIP: 0010:kobject_del+0x6/0x20 Call Trace: btrfs_sysfs_del_qgroups+0xac/0xf0 [btrfs] btrfs_free_qgroup_config+0x63/0x70 [btrfs] close_ctree+0x1f5/0x323 [btrfs] btrfs_put_super+0x15/0x17 [btrfs] generic_shutdown_super+0x72/0x110 kill_anon_super+0x18/0x30 btrfs_kill_super+0x17/0x30 [btrfs] deactivate_locked_super+0x3b/0xa0 deactivate_super+0x40/0x50 cleanup_mnt+0x135/0x190 __cleanup_mnt+0x12/0x20 task_work_run+0x64/0xb0 exit_to_user_mode_prepare+0x18a/0x190 syscall_exit_to_user_mode+0x4f/0x270 do_syscall_64+0x45/0x50 entry_SYSCALL_64_after_hwframe+0x44/0xa9 ---[ end trace 37b7adca5c1d5c5d ]--- [CAUSE] Commit 079ad2fb4bf9 ("kobject: Avoid premature parent object freeing in kobject_cleanup()") changed kobject_del() that it no longer accepts NULL pointer. Before that commit, kobject_del() and kobject_put() all accept NULL pointers and just ignore such NULL pointers. But that mentioned commit needs to access the parent node, killing the old NULL pointer behavior. Unfortunately btrfs is relying on that hidden feature thus we will trigger such NULL pointer dereference. [FIX] Instead of just saving several lines, do proper fs_info->qgroups_kobj check before calling kobject_del() and kobject_put(). Signed-off-by: Qu Wenruo <wqu@suse.com> --- fs/btrfs/compression.c | 10 +++++++--- 1 file changed, 7 insertions(+), 3 deletions(-)