From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from aserp1040.oracle.com ([141.146.126.69]:18661 "EHLO aserp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750971AbbJZJWv (ORCPT ); Mon, 26 Oct 2015 05:22:51 -0400 Subject: Re: [PATCH 1/2 v2] Btrfs: fix regression when running delayed references To: fdmanana@kernel.org, linux-btrfs@vger.kernel.org References: <1445767453-16233-1-git-send-email-fdmanana@kernel.org> Cc: stephane_btrfs@lesimple.fr, Filipe Manana From: Liu Bo Message-ID: <562DF0D8.20502@oracle.com> Date: Mon, 26 Oct 2015 17:22:32 +0800 MIME-Version: 1.0 In-Reply-To: <1445767453-16233-1-git-send-email-fdmanana@kernel.org> Content-Type: text/plain; charset=utf-8; format=flowed Sender: linux-btrfs-owner@vger.kernel.org List-ID: On 10/25/2015 06:04 PM, fdmanana@kernel.org wrote: > From: Filipe Manana > > In the kernel 4.2 merge window we had a refactoring/rework of the delayed > references implementation in order to fix certain problems with qgroups. > However that rework introduced one more regression that leads to the > following trace when running delayed references for metadata: > > [35908.064664] kernel BUG at fs/btrfs/extent-tree.c:1832! > [35908.065201] invalid opcode: 0000 [#1] PREEMPT SMP DEBUG_PAGEALLOC > [35908.065201] Modules linked in: dm_flakey dm_mod btrfs crc32c_generic xor raid6_pq nfsd auth_rpcgss oid_registry nfs_acl nfs lockd grace fscache sunrpc loop fuse parport_pc psmouse i2 > [35908.065201] CPU: 14 PID: 15014 Comm: kworker/u32:9 Tainted: G W 4.3.0-rc5-btrfs-next-17+ #1 > [35908.065201] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.8.1-0-g4adadbd-20150316_085822-nilsson.home.kraxel.org 04/01/2014 > [35908.065201] Workqueue: btrfs-extent-refs btrfs_extent_refs_helper [btrfs] > [35908.065201] task: ffff880114b7d780 ti: ffff88010c4c8000 task.ti: ffff88010c4c8000 > [35908.065201] RIP: 0010:[] [] insert_inline_extent_backref+0x52/0xb1 [btrfs] > [35908.065201] RSP: 0018:ffff88010c4cbb08 EFLAGS: 00010293 > [35908.065201] RAX: 0000000000000000 RBX: ffff88008a661000 RCX: 0000000000000000 > [35908.065201] RDX: ffffffffa04dd58f RSI: 0000000000000001 RDI: 0000000000000000 > [35908.065201] RBP: ffff88010c4cbb40 R08: 0000000000001000 R09: ffff88010c4cb9f8 > [35908.065201] R10: 0000000000000000 R11: 000000000000002c R12: 0000000000000000 > [35908.065201] R13: ffff88020a74c578 R14: 0000000000000000 R15: 0000000000000000 > [35908.065201] FS: 0000000000000000(0000) GS:ffff88023edc0000(0000) knlGS:0000000000000000 > [35908.065201] CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b > [35908.065201] CR2: 00000000015e8708 CR3: 0000000102185000 CR4: 00000000000006e0 > [35908.065201] Stack: > [35908.065201] ffff88010c4cbb18 0000000000000f37 ffff88020a74c578 ffff88015a408000 > [35908.065201] ffff880154a44000 0000000000000000 0000000000000005 ffff88010c4cbbd8 > [35908.065201] ffffffffa0492b9a 0000000000000005 0000000000000000 0000000000000000 > [35908.065201] Call Trace: > [35908.065201] [] __btrfs_inc_extent_ref+0x8b/0x208 [btrfs] > [35908.065201] [] ? __btrfs_run_delayed_refs+0x4d4/0xd33 [btrfs] > [35908.065201] [] __btrfs_run_delayed_refs+0xafa/0xd33 [btrfs] > [35908.065201] [] ? join_transaction.isra.10+0x25/0x41f [btrfs] > [35908.065201] [] ? join_transaction.isra.10+0xa8/0x41f [btrfs] > [35908.065201] [] btrfs_run_delayed_refs+0x75/0x1dd [btrfs] > [35908.065201] [] delayed_ref_async_start+0x3c/0x7b [btrfs] > [35908.065201] [] normal_work_helper+0x14c/0x32a [btrfs] > [35908.065201] [] btrfs_extent_refs_helper+0x12/0x14 [btrfs] > [35908.065201] [] process_one_work+0x24a/0x4ac > [35908.065201] [] worker_thread+0x206/0x2c2 > [35908.065201] [] ? rescuer_thread+0x2cb/0x2cb > [35908.065201] [] ? rescuer_thread+0x2cb/0x2cb > [35908.065201] [] kthread+0xef/0xf7 > [35908.065201] [] ? kthread_parkme+0x24/0x24 > [35908.065201] [] ret_from_fork+0x3f/0x70 > [35908.065201] [] ? kthread_parkme+0x24/0x24 > [35908.065201] Code: 6a 01 41 56 41 54 ff 75 10 41 51 4d 89 c1 49 89 c8 48 8d 4d d0 e8 f6 f1 ff ff 48 83 c4 28 85 c0 75 2c 49 81 fc ff 00 00 00 77 02 <0f> 0b 4c 8b 45 30 8b 4d 28 45 31 > [35908.065201] RIP [] insert_inline_extent_backref+0x52/0xb1 [btrfs] > [35908.065201] RSP > [35908.310885] ---[ end trace fe4299baf0666457 ]--- > > This happens because the new delayed references code no longer merges > delayed references that have different sequence values. The following > steps are an example sequence leading to this issue: > > 1) Transaction N starts, fs_info->tree_mod_seq has value 0; > > 2) Extent buffer (btree node) A is allocated, delayed reference Ref1 for > bytenr A is created, with a value of 1 and a seq value of 0; > > 3) fs_info->tree_mod_seq is incremented to 1; > > 4) Extent buffer A is deleted through btrfs_del_items(), which calls > btrfs_del_leaf(), which in turn calls btrfs_free_tree_block(). The > later returns the metadata extent associated to extent buffer A to > the free space cache (the range is not pinned), because the extent > buffer was created in the current transaction (N) and writeback never > happened for the extent buffer (flag BTRFS_HEADER_FLAG_WRITTEN not set > in the extent buffer). > This creates the delayed reference Ref2 for bytenr A, with a value > of -1 and a seq value of 1; > > 5) Delayed reference Ref2 is not merged with Ref1 when we create it, > because they have different sequence numbers (decided at > add_delayed_ref_tail_merge()); > > 6) fs_info->tree_mod_seq is incremented to 2; > > 7) Some task attempts to allocate a new extent buffer (done at > extent-tree.c:find_free_extent()), but due to heavy fragmentation > and running low on metadata space the clustered allocation fails > and we fall back to unclustered allocation, which finds the > extent at offset A, so a new extent buffer at offset A is allocated. > This creates delayed reference Ref3 for bytenr A, with a value of -1 The value is 1 if we create an eb. Others look good. Reviewed-by: Liu Bo thanks, -liubo > and a seq value of 2; > > 8) Ref3 is not merged neither with Ref2 nor Ref1, again because they > all have different seq values; > > 9) We start running the delayed references (__btrfs_run_delayed_refs()); > > 10) The delayed Ref1 is the first one being applied, which ends up > creating an inline extent backref in the extent tree; > > 10) Next the delayed reference Ref3 is selected for execution, and not > Ref2, because select_delayed_ref() always gives a preference for > positive references (that have an action of BTRFS_ADD_DELAYED_REF); > > 11) When running Ref3 we encounter alreay the inline extent backref > in the extent tree at insert_inline_extent_backref(), which makes > us hit the following BUG_ON: > > BUG_ON(owner < BTRFS_FIRST_FREE_OBJECTID); > > This is always true because owner corresponds to the level of the > extent buffer/btree node in the btree. > > For the scenario described above we hit the BUG_ON because we never merge > references that have different seq values. > > We used to do the merging before the 4.2 kernel, more specifically, before > the commmits: > > c6fc24549960 ("btrfs: delayed-ref: Use list to replace the ref_root in ref_head.") > c43d160fcd5e ("btrfs: delayed-ref: Cleanup the unneeded functions.") > > This issue became more exposed after the following change that was added > to 4.2 as well: > > cffc3374e567 ("Btrfs: fix order by which delayed references are run") > > Which in turn fixed another regression by the two commits previously > mentioned. > > So fix this by bringing back the delayed reference merge code, with the > proper adaptations so that it operates against the new data structure > (linked list vs old red black tree implementation). > > This issue was hit running fstest btrfs/063 in a loop. Several people have > reported this issue in the mailing list when running on kernels 4.2+. > > Very special thanks to Stéphane Lesimple for helping debugging this issue > and testing this fix on his multi terabyte filesystem (which took more > than one day to balance alone, plus fsck, etc). > > Fixes: c6fc24549960 ("btrfs: delayed-ref: Use list to replace the ref_root in ref_head.") > Reported-by: Peter Becker > Reported-by: Stéphane Lesimple > Tested-by: Stéphane Lesimple > Reported-by: Malte Schröder > Reported-by: Derek Dongray > Reported-by: Erkki Seppala > Cc: stable@vger.kernel.org # 4.2+ > Signed-off-by: Filipe Manana > --- > > V2: No code changes. Added Stéphane's Tested-by tag and made patch > part of a 2 fixes series, to reflect the other remaining fix > depends on this one. > > fs/btrfs/delayed-ref.c | 113 +++++++++++++++++++++++++++++++++++++++++++++++++ > fs/btrfs/extent-tree.c | 14 ++++++ > 2 files changed, 127 insertions(+) > > diff --git a/fs/btrfs/delayed-ref.c b/fs/btrfs/delayed-ref.c > index ac3e81d..4832943 100644 > --- a/fs/btrfs/delayed-ref.c > +++ b/fs/btrfs/delayed-ref.c > @@ -197,6 +197,119 @@ static inline void drop_delayed_ref(struct btrfs_trans_handle *trans, > trans->delayed_ref_updates--; > } > > +static bool merge_ref(struct btrfs_trans_handle *trans, > + struct btrfs_delayed_ref_root *delayed_refs, > + struct btrfs_delayed_ref_head *head, > + struct btrfs_delayed_ref_node *ref, > + u64 seq) > +{ > + struct btrfs_delayed_ref_node *next; > + bool done = false; > + > + next = list_first_entry(&head->ref_list, struct btrfs_delayed_ref_node, > + list); > + while (!done && &next->list != &head->ref_list) { > + int mod; > + struct btrfs_delayed_ref_node *next2; > + > + next2 = list_next_entry(next, list); > + > + if (next == ref) > + goto next; > + > + if (seq && next->seq >= seq) > + goto next; > + > + if (next->type != ref->type || next->no_quota != ref->no_quota) > + goto next; > + > + if ((ref->type == BTRFS_TREE_BLOCK_REF_KEY || > + ref->type == BTRFS_SHARED_BLOCK_REF_KEY) && > + comp_tree_refs(btrfs_delayed_node_to_tree_ref(ref), > + btrfs_delayed_node_to_tree_ref(next), > + ref->type)) > + goto next; > + if ((ref->type == BTRFS_EXTENT_DATA_REF_KEY || > + ref->type == BTRFS_SHARED_DATA_REF_KEY) && > + comp_data_refs(btrfs_delayed_node_to_data_ref(ref), > + btrfs_delayed_node_to_data_ref(next))) > + goto next; > + > + if (ref->action == next->action) { > + mod = next->ref_mod; > + } else { > + if (ref->ref_mod < next->ref_mod) { > + swap(ref, next); > + done = true; > + } > + mod = -next->ref_mod; > + } > + > + drop_delayed_ref(trans, delayed_refs, head, next); > + ref->ref_mod += mod; > + if (ref->ref_mod == 0) { > + drop_delayed_ref(trans, delayed_refs, head, ref); > + done = true; > + } else { > + /* > + * Can't have multiples of the same ref on a tree block. > + */ > + WARN_ON(ref->type == BTRFS_TREE_BLOCK_REF_KEY || > + ref->type == BTRFS_SHARED_BLOCK_REF_KEY); > + } > +next: > + next = next2; > + } > + > + return done; > +} > + > +void btrfs_merge_delayed_refs(struct btrfs_trans_handle *trans, > + struct btrfs_fs_info *fs_info, > + struct btrfs_delayed_ref_root *delayed_refs, > + struct btrfs_delayed_ref_head *head) > +{ > + struct btrfs_delayed_ref_node *ref; > + u64 seq = 0; > + > + assert_spin_locked(&head->lock); > + > + if (list_empty(&head->ref_list)) > + return; > + > + /* We don't have too many refs to merge for data. */ > + if (head->is_data) > + return; > + > + spin_lock(&fs_info->tree_mod_seq_lock); > + if (!list_empty(&fs_info->tree_mod_seq_list)) { > + struct seq_list *elem; > + > + elem = list_first_entry(&fs_info->tree_mod_seq_list, > + struct seq_list, list); > + seq = elem->seq; > + } > + spin_unlock(&fs_info->tree_mod_seq_lock); > + > + ref = list_first_entry(&head->ref_list, struct btrfs_delayed_ref_node, > + list); > + while (&ref->list != &head->ref_list) { > + if (seq && ref->seq >= seq) > + goto next; > + > + if (merge_ref(trans, delayed_refs, head, ref, seq)) { > + if (list_empty(&head->ref_list)) > + break; > + ref = list_first_entry(&head->ref_list, > + struct btrfs_delayed_ref_node, > + list); > + continue; > + } > +next: > + ref = list_next_entry(ref, list); > + } > +} > + > int btrfs_check_delayed_seq(struct btrfs_fs_info *fs_info, > struct btrfs_delayed_ref_root *delayed_refs, > u64 seq) > diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c > index 2df4bc7..dd5756c 100644 > --- a/fs/btrfs/extent-tree.c > +++ b/fs/btrfs/extent-tree.c > @@ -2433,7 +2433,21 @@ static noinline int __btrfs_run_delayed_refs(struct btrfs_trans_handle *trans, > } > } > > + /* > + * We need to try and merge add/drops of the same ref since we > + * can run into issues with relocate dropping the implicit ref > + * and then it being added back again before the drop can > + * finish. If we merged anything we need to re-loop so we can > + * get a good ref. > + * Or we can get node references of the same type that weren't > + * merged when created due to bumps in the tree mod seq, and > + * we need to merge them to prevent adding an inline extent > + * backref before dropping it (triggering a BUG_ON at > + * insert_inline_extent_backref()). > + */ > spin_lock(&locked_ref->lock); > + btrfs_merge_delayed_refs(trans, fs_info, delayed_refs, > + locked_ref); > > /* > * locked_ref is the head node, so we have to go one >