From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mout.gmx.net ([212.227.17.20]:50037 "EHLO mout.gmx.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752693AbeDLLtM (ORCPT ); Thu, 12 Apr 2018 07:49:12 -0400 Subject: Re: [PATCH 2/2] btrfs: Do first key check under proper lock context To: Nikolay Borisov , Qu Wenruo , linux-btrfs@vger.kernel.org References: <20180412100003.31907-1-wqu@suse.com> <20180412100003.31907-2-wqu@suse.com> From: Qu Wenruo Message-ID: Date: Thu, 12 Apr 2018 19:48:59 +0800 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Sender: linux-btrfs-owner@vger.kernel.org List-ID: On 2018年04月12日 18:59, Nikolay Borisov wrote: > > > On 12.04.2018 13:00, Qu Wenruo wrote: >> The original first key check is handled in >> btree_read_extent_buffer_pages(), which is good enough for level check, >> but to verify first key, we need at least read lock on the extent >> buffer, or we can hit some race and cause false alert. >> >> Fix it by adding new verifcation function: btrfs_verify_first_key(), >> which will first check lock context of both parent and child extent >> buffer, and only when we have proper lock hold (write or read lock if > So if the extent buffer is not in commit root, i.e it's active buffer in > current transaction (am I right?) That's right. > then we need write lock? It's not entirely clearly from that sentence. Not really write lock. Either read or write (both spinning and blocking) is OK here. > >> extent buffer is not in commit root) we will verify the first key. >> >> Most of the verification happens in ctree.c after function call like >> read_tree_block(), read_node_slot() and read_block_for_search(), and >> only call btrfs_verify_first_key() after we acquire read/write lock. >> >> Also, since first_key check is not as good as level and could easily >> trigger false alerts due to lock context, put it under >> CONFIG_BTRFS_FS_CHECK_INTEGRITY to avoid damage to end user. > > Why is first_key check not as good as level Several reasons. 1) Level tree check can prevent loop/nodes underflow caused by level mismatch, but first_key can't One problem we're trying to solve is, when level 1 node points to another level 1 tree, we can still try to read next level tree block. Which could underflow level. first_key check can't really handle it. 2) first_key needs extra lock to read out needed info, while level check doesn't (hence easier and harder to cause false alert) For a given tree block, its level won't change either for active eb (modified in current trans) or committed eb. But for first_key, we need proper lock to avoid race. For short, first key check needs a lot of carefully reviewed check timing and error handlers, while most problem could be exposed by level check far before it hits first_key check. > and why could it trigger > false alert, given this patch allegedly implements it under proper lock > context, thus eliminating false positives. I mean the old and merged first_key check patch. Thanks, Qu > >> >> Signed-off-by: Qu Wenruo >> --- >> fs/btrfs/ctree.c | 69 ++++++++++++++++++++++++++++++++++++++++++ >> fs/btrfs/ctree.h | 58 +++++++++++++++++++++++++++++++++++ >> fs/btrfs/extent-tree.c | 6 ++++ >> fs/btrfs/qgroup.c | 5 +++ >> fs/btrfs/ref-verify.c | 6 ++++ >> fs/btrfs/relocation.c | 13 ++++++++ >> 6 files changed, 157 insertions(+) >> >> diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c >> index e044b51a2789..57721aead371 100644 >> --- a/fs/btrfs/ctree.c >> +++ b/fs/btrfs/ctree.c >> @@ -1649,6 +1649,11 @@ int btrfs_realloc_node(struct btrfs_trans_handle *trans, >> >> btrfs_tree_lock(cur); >> btrfs_set_lock_blocking(cur); >> + if (btrfs_verify_first_key(cur, parent, i)) { >> + err = -EUCLEAN; >> + btrfs_tree_unlock(cur); >> + free_extent_buffer(cur); >> + } >> err = __btrfs_cow_block(trans, root, cur, parent, i, >> &cur, search_start, >> min(16 * blocksize, >> @@ -1863,6 +1868,12 @@ static noinline int balance_level(struct btrfs_trans_handle *trans, >> >> btrfs_tree_lock(child); >> btrfs_set_lock_blocking(child); >> + if (btrfs_verify_first_key(child, mid, 0)) { >> + ret = -EUCLEAN; >> + btrfs_tree_unlock(child); >> + free_extent_buffer(child); >> + goto enospc; >> + } >> ret = btrfs_cow_block(trans, root, child, mid, 0, &child); >> if (ret) { >> btrfs_tree_unlock(child); >> @@ -1901,6 +1912,10 @@ static noinline int balance_level(struct btrfs_trans_handle *trans, >> if (left) { >> btrfs_tree_lock(left); >> btrfs_set_lock_blocking(left); >> + if (btrfs_verify_first_key(left, parent, pslot - 1)) { >> + ret = -EUCLEAN; >> + goto enospc; >> + } >> wret = btrfs_cow_block(trans, root, left, >> parent, pslot - 1, &left); >> if (wret) { >> @@ -1916,6 +1931,10 @@ static noinline int balance_level(struct btrfs_trans_handle *trans, >> if (right) { >> btrfs_tree_lock(right); >> btrfs_set_lock_blocking(right); >> + if (btrfs_verify_first_key(right, parent, pslot + 1)) { >> + ret = -EUCLEAN; >> + goto enospc; >> + } >> wret = btrfs_cow_block(trans, root, right, >> parent, pslot + 1, &right); >> if (wret) { >> @@ -2079,6 +2098,8 @@ static noinline int push_nodes_for_insert(struct btrfs_trans_handle *trans, >> >> btrfs_tree_lock(left); >> btrfs_set_lock_blocking(left); >> + if (btrfs_verify_first_key(left, parent, pslot - 1)) >> + goto left_out; >> >> left_nr = btrfs_header_nritems(left); >> if (left_nr >= BTRFS_NODEPTRS_PER_BLOCK(fs_info) - 1) { >> @@ -2119,6 +2140,7 @@ static noinline int push_nodes_for_insert(struct btrfs_trans_handle *trans, >> } >> return 0; >> } >> +left_out: >> btrfs_tree_unlock(left); >> free_extent_buffer(left); >> } >> @@ -2134,6 +2156,8 @@ static noinline int push_nodes_for_insert(struct btrfs_trans_handle *trans, >> >> btrfs_tree_lock(right); >> btrfs_set_lock_blocking(right); >> + if (btrfs_verify_first_key(right, parent, pslot + 1)) >> + goto right_out; >> >> right_nr = btrfs_header_nritems(right); >> if (right_nr >= BTRFS_NODEPTRS_PER_BLOCK(fs_info) - 1) { >> @@ -2174,6 +2198,7 @@ static noinline int push_nodes_for_insert(struct btrfs_trans_handle *trans, >> } >> return 0; >> } >> +right_out: >> btrfs_tree_unlock(right); >> free_extent_buffer(right); >> } >> @@ -2868,6 +2893,11 @@ int btrfs_search_slot(struct btrfs_trans_handle *trans, struct btrfs_root *root, >> p->locks[level] = BTRFS_READ_LOCK; >> } >> p->nodes[level] = b; >> + if (btrfs_verify_first_key(b, p->nodes[level + 1], >> + slot)) { >> + ret = -EUCLEAN; >> + goto done; >> + } >> } >> } else { >> p->slots[level] = slot; >> @@ -2981,6 +3011,12 @@ int btrfs_search_old_slot(struct btrfs_root *root, const struct btrfs_key *key, >> goto done; >> } >> >> + /* >> + * NOTE: both parent and child go through >> + * tree_mod_log_rewind(), first key check is no >> + * longer consistent. So no btrfs_verify_first_key() >> + * for this read_block_for_search(). >> + */ >> err = read_block_for_search(root, p, &b, level, >> slot, key); >> if (err == -EAGAIN) >> @@ -3753,6 +3789,8 @@ static int push_leaf_right(struct btrfs_trans_handle *trans, struct btrfs_root >> >> btrfs_tree_lock(right); >> btrfs_set_lock_blocking(right); >> + if (btrfs_verify_first_key(right, upper, slot + 1)) >> + goto out_unlock; >> >> free_space = btrfs_leaf_free_space(fs_info, right); >> if (free_space < data_size) >> @@ -3987,6 +4025,10 @@ static int push_leaf_left(struct btrfs_trans_handle *trans, struct btrfs_root >> >> btrfs_tree_lock(left); >> btrfs_set_lock_blocking(left); >> + if (btrfs_verify_first_key(left, path->nodes[1], slot - 1)) { >> + ret = 1; >> + goto out; >> + } >> >> free_space = btrfs_leaf_free_space(fs_info, left); >> if (free_space < data_size) { >> @@ -5205,6 +5247,12 @@ int btrfs_search_forward(struct btrfs_root *root, struct btrfs_key *min_key, >> } >> >> btrfs_tree_read_lock(cur); >> + if (btrfs_verify_first_key(cur, path->nodes[level], slot)) { >> + btrfs_tree_read_unlock(cur); >> + free_extent_buffer(cur); >> + ret = -EUCLEAN; >> + goto out; >> + } >> >> path->locks[level - 1] = BTRFS_READ_LOCK; >> path->nodes[level - 1] = cur; >> @@ -5232,6 +5280,11 @@ static int tree_move_down(struct btrfs_fs_info *fs_info, >> if (IS_ERR(eb)) >> return PTR_ERR(eb); >> >> + if (btrfs_verify_first_key(eb, path->nodes[*level], >> + path->slots[*level])) { >> + free_extent_buffer(eb); >> + return -EUCLEAN; >> + } >> path->nodes[*level - 1] = eb; >> path->slots[*level - 1] = 0; >> (*level)--; >> @@ -5786,6 +5839,14 @@ int btrfs_next_old_leaf(struct btrfs_root *root, struct btrfs_path *path, >> BTRFS_READ_LOCK); >> } >> next_rw_lock = BTRFS_READ_LOCK; >> + if (btrfs_verify_first_key(next, path->nodes[level], >> + slot)) { >> + ret = -EUCLEAN; >> + btrfs_tree_read_unlock(next); >> + free_extent_buffer(next); >> + btrfs_release_path(path); >> + goto done; >> + } >> } >> break; >> } >> @@ -5823,6 +5884,14 @@ int btrfs_next_old_leaf(struct btrfs_root *root, struct btrfs_path *path, >> BTRFS_READ_LOCK); >> } >> next_rw_lock = BTRFS_READ_LOCK; >> + if (btrfs_verify_first_key(next, path->nodes[level], >> + 0)) { >> + ret = -EUCLEAN; >> + btrfs_tree_read_unlock(next); >> + free_extent_buffer(next); >> + btrfs_release_path(path); >> + goto done; >> + } >> } >> } >> ret = 0; >> diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h >> index 0eb55825862a..033d8ae027c3 100644 >> --- a/fs/btrfs/ctree.h >> +++ b/fs/btrfs/ctree.h >> @@ -44,6 +44,7 @@ >> #include "extent_io.h" >> #include "extent_map.h" >> #include "async-thread.h" >> +#include "print-tree.h" >> >> struct btrfs_trans_handle; >> struct btrfs_transaction; >> @@ -3752,4 +3753,61 @@ static inline int btrfs_is_testing(struct btrfs_fs_info *fs_info) >> #endif >> return 0; >> } >> + >> +/* >> + * Verify the first key of an extent buffer matches with its parent pointer. >> + * >> + * For tree blocks in current transaction, caller should hold at least read lock >> + * for both @eb and @parent to avoid race. >> + * While for tree blocks in commit root, no such requirement. >> + */ >> +static inline int btrfs_verify_first_key(struct extent_buffer *eb, >> + struct extent_buffer *parent, int slot) >> +{ >> +#ifdef CONFIG_BTRFS_FS_CHECK_INTEGRITY >> + struct btrfs_key parent_key; >> + struct btrfs_key found_key; >> + struct btrfs_fs_info *fs_info; >> + u64 transid = 0; >> + int ret; >> + >> + if (!parent || !eb) >> + return 0; >> + fs_info = parent->fs_info; >> + transid = fs_info->last_trans_committed; >> + /* >> + * For first_key check, we need to ensure we have proper lock hold, >> + * or the content may change and cause false alert. >> + */ >> + if (btrfs_header_generation(eb) > transid && >> + !atomic_read(&eb->read_locks) && !atomic_read(&eb->write_locks)) { >> + WARN_ON(1); >> + return 0; >> + } >> + if (btrfs_header_generation(parent) > transid && >> + !atomic_read(&parent->read_locks) && >> + !atomic_read(&parent->write_locks)) { >> + WARN_ON(1); >> + return 0; >> + } >> + btrfs_node_key_to_cpu(parent, &parent_key, slot); >> + if (btrfs_header_level(eb)) >> + btrfs_node_key_to_cpu(eb, &found_key, 0); >> + else >> + btrfs_item_key_to_cpu(eb, &found_key, 0); >> + ret = btrfs_comp_cpu_keys(&found_key, &parent_key); >> + if (ret) { >> + WARN_ON(ret); >> + btrfs_err(fs_info, >> +"tree first key mismatch detected, bytenr=%llu key expected=(%llu, %u, %llu) has=(%llu, %u, %llu)", >> + eb->start, parent_key.objectid, parent_key.type, >> + parent_key.offset, found_key.objectid, >> + found_key.type, found_key.offset); >> + } >> + return ret; >> +#else >> + return 0; >> +#endif /* CONFIG_BTRFS_FS_CHECK_INTEGRITY */ >> +} >> + >> #endif >> diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c >> index f080834e4dd0..17bd22a54281 100644 >> --- a/fs/btrfs/extent-tree.c >> +++ b/fs/btrfs/extent-tree.c >> @@ -8807,6 +8807,12 @@ static noinline int do_walk_down(struct btrfs_trans_handle *trans, >> } >> btrfs_tree_lock(next); >> btrfs_set_lock_blocking(next); >> + if (btrfs_verify_first_key(next, path->nodes[level], >> + path->slots[level])) { >> + btrfs_tree_unlock(next); >> + free_extent_buffer(next); >> + goto out_unlock; >> + } >> } >> >> level--; >> diff --git a/fs/btrfs/qgroup.c b/fs/btrfs/qgroup.c >> index c7f129356966..4c53954297d8 100644 >> --- a/fs/btrfs/qgroup.c >> +++ b/fs/btrfs/qgroup.c >> @@ -1744,6 +1744,11 @@ int btrfs_qgroup_trace_subtree(struct btrfs_trans_handle *trans, >> >> btrfs_tree_read_lock(eb); >> btrfs_set_lock_blocking_rw(eb, BTRFS_READ_LOCK); >> + if (btrfs_verify_first_key(eb, path->nodes[level + 1], >> + parent_slot)) { >> + ret = -EUCLEAN; >> + goto out; >> + } >> path->locks[level] = BTRFS_READ_LOCK_BLOCKING; >> >> ret = btrfs_qgroup_trace_extent(trans, fs_info, >> diff --git a/fs/btrfs/ref-verify.c b/fs/btrfs/ref-verify.c >> index 6d856eabf34a..b996ca1fd9dc 100644 >> --- a/fs/btrfs/ref-verify.c >> +++ b/fs/btrfs/ref-verify.c >> @@ -593,6 +593,12 @@ static int walk_down_tree(struct btrfs_root *root, struct btrfs_path *path, >> } >> btrfs_tree_read_lock(eb); >> btrfs_set_lock_blocking_rw(eb, BTRFS_READ_LOCK); >> + if (btrfs_verify_first_key(eb, path->nodes[level], >> + path->slots[level])) { >> + btrfs_tree_read_unlock_blocking(eb); >> + free_extent_buffer(eb); >> + return -EUCLEAN; >> + } >> path->nodes[level-1] = eb; >> path->slots[level-1] = 0; >> path->locks[level-1] = BTRFS_READ_LOCK_BLOCKING; >> diff --git a/fs/btrfs/relocation.c b/fs/btrfs/relocation.c >> index 74db4694d776..74a088fbdac4 100644 >> --- a/fs/btrfs/relocation.c >> +++ b/fs/btrfs/relocation.c >> @@ -1888,6 +1888,13 @@ int replace_path(struct btrfs_trans_handle *trans, >> break; >> } >> btrfs_tree_lock(eb); >> + if (btrfs_verify_first_key(eb, parent, slot)) { >> + btrfs_tree_unlock(eb); >> + free_extent_buffer(eb); >> + ret = -EUCLEAN; >> + break; >> + } >> + >> if (cow) { >> ret = btrfs_cow_block(trans, dest, eb, parent, >> slot, &eb); >> @@ -2793,6 +2800,12 @@ static int do_relocation(struct btrfs_trans_handle *trans, >> } >> btrfs_tree_lock(eb); >> btrfs_set_lock_blocking(eb); >> + if (btrfs_verify_first_key(eb, upper->eb, slot)) { >> + btrfs_tree_unlock(eb); >> + free_extent_buffer(eb); >> + err = -EUCLEAN; >> + goto next; >> + } >> >> if (!node->eb) { >> ret = btrfs_cow_block(trans, root, eb, upper->eb, >> > -- > To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html >