This is a note to let you know that I've just added the patch titled btrfs: do not cleanup upper nodes in btrfs_backref_cleanup_node to the 5.10-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: btrfs-do-not-cleanup-upper-nodes-in-btrfs_backref_cleanup_node.patch and it can be found in the queue-5.10 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From 7e2a870a599d4699a626ec26430c7a1ab14a2a49 Mon Sep 17 00:00:00 2001 From: Josef Bacik <josef@xxxxxxxxxxxxxx> Date: Wed, 16 Dec 2020 11:22:16 -0500 Subject: btrfs: do not cleanup upper nodes in btrfs_backref_cleanup_node From: Josef Bacik <josef@xxxxxxxxxxxxxx> commit 7e2a870a599d4699a626ec26430c7a1ab14a2a49 upstream. Zygo reported the following panic when testing my error handling patches for relocation: kernel BUG at fs/btrfs/backref.c:2545! invalid opcode: 0000 [#1] SMP KASAN PTI CPU: 3 PID: 8472 Comm: btrfs Tainted: G W 14 Hardware name: QEMU Standard PC (i440FX + PIIX, Call Trace: btrfs_backref_error_cleanup+0x4df/0x530 build_backref_tree+0x1a5/0x700 ? _raw_spin_unlock+0x22/0x30 ? release_extent_buffer+0x225/0x280 ? free_extent_buffer.part.52+0xd7/0x140 relocate_tree_blocks+0x2a6/0xb60 ? kasan_unpoison_shadow+0x35/0x50 ? do_relocation+0xc10/0xc10 ? kasan_kmalloc+0x9/0x10 ? kmem_cache_alloc_trace+0x6a3/0xcb0 ? free_extent_buffer.part.52+0xd7/0x140 ? rb_insert_color+0x342/0x360 ? add_tree_block.isra.36+0x236/0x2b0 relocate_block_group+0x2eb/0x780 ? merge_reloc_roots+0x470/0x470 btrfs_relocate_block_group+0x26e/0x4c0 btrfs_relocate_chunk+0x52/0x120 btrfs_balance+0xe2e/0x18f0 ? pvclock_clocksource_read+0xeb/0x190 ? btrfs_relocate_chunk+0x120/0x120 ? lock_contended+0x620/0x6e0 ? do_raw_spin_lock+0x1e0/0x1e0 ? do_raw_spin_unlock+0xa8/0x140 btrfs_ioctl_balance+0x1f9/0x460 btrfs_ioctl+0x24c8/0x4380 ? __kasan_check_read+0x11/0x20 ? check_chain_key+0x1f4/0x2f0 ? __asan_loadN+0xf/0x20 ? btrfs_ioctl_get_supported_features+0x30/0x30 ? kvm_sched_clock_read+0x18/0x30 ? check_chain_key+0x1f4/0x2f0 ? lock_downgrade+0x3f0/0x3f0 ? handle_mm_fault+0xad6/0x2150 ? do_vfs_ioctl+0xfc/0x9d0 ? ioctl_file_clone+0xe0/0xe0 ? check_flags.part.50+0x6c/0x1e0 ? check_flags.part.50+0x6c/0x1e0 ? check_flags+0x26/0x30 ? lock_is_held_type+0xc3/0xf0 ? syscall_enter_from_user_mode+0x1b/0x60 ? do_syscall_64+0x13/0x80 ? rcu_read_lock_sched_held+0xa1/0xd0 ? __kasan_check_read+0x11/0x20 ? __fget_light+0xae/0x110 __x64_sys_ioctl+0xc3/0x100 do_syscall_64+0x37/0x80 entry_SYSCALL_64_after_hwframe+0x44/0xa9 This occurs because of this check if (RB_EMPTY_NODE(&upper->rb_node)) BUG_ON(!list_empty(&node->upper)); As we are dropping the backref node, if we discover that our upper node in the edge we just cleaned up isn't linked into the cache that we are now done with this node, thus the BUG_ON(). However this is an erroneous assumption, as we will look up all the references for a node first, and then process the pending edges. All of the 'upper' nodes in our pending edges won't be in the cache's rb_tree yet, because they haven't been processed. We could very well have many edges still left to cleanup on this node. The fact is we simply do not need this check, we can just process all of the edges only for this node, because below this check we do the following if (list_empty(&upper->lower)) { list_add_tail(&upper->lower, &cache->leaves); upper->lowest = 1; } If the upper node truly isn't used yet, then we add it to the cache->leaves list to be cleaned up later. If it is still used then the last child node that has it linked into its node will add it to the leaves list and then it will be cleaned up. Fix this problem by dropping this logic altogether. With this fix I no longer see the panic when testing with error injection in the backref code. CC: stable@xxxxxxxxxxxxxxx # 4.4+ Reviewed-by: Qu Wenruo <wqu@xxxxxxxx> Signed-off-by: Josef Bacik <josef@xxxxxxxxxxxxxx> Signed-off-by: David Sterba <dsterba@xxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- fs/btrfs/backref.c | 7 ------- 1 file changed, 7 deletions(-) --- a/fs/btrfs/backref.c +++ b/fs/btrfs/backref.c @@ -2548,13 +2548,6 @@ void btrfs_backref_cleanup_node(struct b list_del(&edge->list[UPPER]); btrfs_backref_free_edge(cache, edge); - if (RB_EMPTY_NODE(&upper->rb_node)) { - BUG_ON(!list_empty(&node->upper)); - btrfs_backref_drop_node(cache, node); - node = upper; - node->lowest = 1; - continue; - } /* * Add the node to leaf node list if no other child block * cached. Patches currently in stable-queue which might be from josef@xxxxxxxxxxxxxx are queue-5.10/btrfs-abort-the-transaction-if-we-fail-to-inc-ref-in-btrfs_copy_root.patch queue-5.10/btrfs-handle-space_info-total_bytes_pinned-inside-the-delayed-ref-itself.patch queue-5.10/btrfs-splice-remaining-dirty_bg-s-onto-the-transaction-dirty-bg-list.patch queue-5.10/btrfs-do-not-warn-if-we-can-t-find-the-reloc-root-when-looking-up-backref.patch queue-5.10/btrfs-fix-reloc-root-leak-with-0-ref-reloc-roots-on-recovery.patch queue-5.10/btrfs-do-not-cleanup-upper-nodes-in-btrfs_backref_cleanup_node.patch queue-5.10/btrfs-account-for-new-extents-being-deleted-in-total_bytes_pinned.patch queue-5.10/proc-use-kvzalloc-for-our-kernel-buffer.patch queue-5.10/btrfs-add-asserts-for-deleting-backref-cache-nodes.patch