From: Qu Wenruo wqu@suse.com
commit 51415b6c1b117e223bc083e30af675cb5c5498f3 upstream.
[BUG] When balance is canceled, there is a pretty high chance that unmounting the fs can lead to lead the NULL pointer dereference:
BTRFS warning (device dm-3): page private not zero on page 223158272 ... BTRFS warning (device dm-3): page private not zero on page 223162368 BTRFS error (device dm-3): leaked root 18446744073709551608-304 refcount 1 BUG: kernel NULL pointer dereference, address: 0000000000000168 #PF: supervisor read access in kernel mode #PF: error_code(0x0000) - not-present page PGD 0 P4D 0 Oops: 0000 [#1] PREEMPT SMP NOPTI CPU: 2 PID: 5793 Comm: umount Tainted: G O 5.7.0-rc5-custom+ #53 Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015 RIP: 0010:__lock_acquire+0x5dc/0x24c0 Call Trace: lock_acquire+0xab/0x390 _raw_spin_lock+0x39/0x80 btrfs_release_extent_buffer_pages+0xd7/0x200 [btrfs] release_extent_buffer+0xb2/0x170 [btrfs] free_extent_buffer+0x66/0xb0 [btrfs] btrfs_put_root+0x8e/0x130 [btrfs] btrfs_check_leaked_roots.cold+0x5/0x5d [btrfs] btrfs_free_fs_info+0xe5/0x120 [btrfs] btrfs_kill_super+0x1f/0x30 [btrfs] deactivate_locked_super+0x3b/0x80 deactivate_super+0x3e/0x50 cleanup_mnt+0x109/0x160 __cleanup_mnt+0x12/0x20 task_work_run+0x67/0xa0 exit_to_usermode_loop+0xc5/0xd0 syscall_return_slowpath+0x205/0x360 do_syscall_64+0x6e/0xb0 entry_SYSCALL_64_after_hwframe+0x49/0xb3 RIP: 0033:0x7fd028ef740b
[CAUSE] When balance is canceled, all reloc roots are marked as orphan, and orphan reloc roots are going to be cleaned up.
However for orphan reloc roots and merged reloc roots, their lifespan are quite different:
Merged reloc roots | Orphan reloc roots by cancel -------------------------------------------------------------------- create_reloc_root() | create_reloc_root() |- refs == 1 | |- refs == 1 | btrfs_grab_root(reloc_root); | btrfs_grab_root(reloc_root); |- refs == 2 | |- refs == 2 | root->reloc_root = reloc_root; | root->reloc_root = reloc_root; >>> No difference so far <<< | prepare_to_merge() | prepare_to_merge() |- btrfs_set_root_refs(item, 1);| |- if (!err) (err == -EINTR) | merge_reloc_roots() | merge_reloc_roots() |- merge_reloc_root() | |- Doing nothing to put reloc root |- insert_dirty_subvol() | |- refs == 2 |- __del_reloc_root() | |- btrfs_put_root() | |- refs == 1 | >>> Now orphan reloc roots still have refs 2 <<< | clean_dirty_subvols() | clean_dirty_subvols() |- btrfs_drop_snapshot() | |- btrfS_drop_snapshot() |- reloc_root get freed | |- reloc_root still has refs 2 | related ebs get freed, but | reloc_root still recorded in | allocated_roots btrfs_check_leaked_roots() | btrfs_check_leaked_roots() |- No leaked roots | |- Leaked reloc_roots detected | |- btrfs_put_root() | |- free_extent_buffer(root->node); | |- eb already freed, caused NULL | pointer dereference
[FIX] The fix is to clear fs_root->reloc_root and put it at merge_reloc_roots() time, so that we won't leak reloc roots.
Fixes: d2311e698578 ("btrfs: relocation: Delay reloc tree deletion after merge_reloc_roots") CC: stable@vger.kernel.org # 5.1+ Tested-by: Johannes Thumshirn johannes.thumshirn@wdc.com Signed-off-by: Qu Wenruo wqu@suse.com Signed-off-by: David Sterba dsterba@suse.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- fs/btrfs/relocation.c | 12 +++++++++--- 1 file changed, 9 insertions(+), 3 deletions(-)
--- a/fs/btrfs/relocation.c +++ b/fs/btrfs/relocation.c @@ -2624,12 +2624,10 @@ again: reloc_root = list_entry(reloc_roots.next, struct btrfs_root, root_list);
+ root = read_fs_root(fs_info, reloc_root->root_key.offset); if (btrfs_root_refs(&reloc_root->root_item) > 0) { - root = read_fs_root(fs_info, - reloc_root->root_key.offset); BUG_ON(IS_ERR(root)); BUG_ON(root->reloc_root != reloc_root); - ret = merge_reloc_root(rc, root); btrfs_put_root(root); if (ret) { @@ -2639,6 +2637,14 @@ again: goto out; } } else { + if (!IS_ERR(root)) { + if (root->reloc_root == reloc_root) { + root->reloc_root = NULL; + btrfs_put_root(reloc_root); + } + btrfs_put_root(root); + } + list_del_init(&reloc_root->root_list); /* Don't forget to queue this reloc root for cleanup */ list_add_tail(&reloc_root->reloc_dirty_list,