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5417ad6e GKH |
1 | From bfc61c36260ca990937539cd648ede3cd749bc10 Mon Sep 17 00:00:00 2001 |
2 | From: Filipe Manana <fdmanana@suse.com> | |
3 | Date: Wed, 17 Apr 2019 11:30:30 +0100 | |
4 | Subject: Btrfs: do not start a transaction at iterate_extent_inodes() | |
5 | ||
6 | From: Filipe Manana <fdmanana@suse.com> | |
7 | ||
8 | commit bfc61c36260ca990937539cd648ede3cd749bc10 upstream. | |
9 | ||
10 | When finding out which inodes have references on a particular extent, done | |
11 | by backref.c:iterate_extent_inodes(), from the BTRFS_IOC_LOGICAL_INO (both | |
12 | v1 and v2) ioctl and from scrub we use the transaction join API to grab a | |
13 | reference on the currently running transaction, since in order to give | |
14 | accurate results we need to inspect the delayed references of the currently | |
15 | running transaction. | |
16 | ||
17 | However, if there is currently no running transaction, the join operation | |
18 | will create a new transaction. This is inefficient as the transaction will | |
19 | eventually be committed, doing unnecessary IO and introducing a potential | |
20 | point of failure that will lead to a transaction abort due to -ENOSPC, as | |
21 | recently reported [1]. | |
22 | ||
23 | That's because the join, creates the transaction but does not reserve any | |
24 | space, so when attempting to update the root item of the root passed to | |
25 | btrfs_join_transaction(), during the transaction commit, we can end up | |
26 | failling with -ENOSPC. Users of a join operation are supposed to actually | |
27 | do some filesystem changes and reserve space by some means, which is not | |
28 | the case of iterate_extent_inodes(), it is a read-only operation for all | |
29 | contextes from which it is called. | |
30 | ||
31 | The reported [1] -ENOSPC failure stack trace is the following: | |
32 | ||
33 | heisenberg kernel: ------------[ cut here ]------------ | |
34 | heisenberg kernel: BTRFS: Transaction aborted (error -28) | |
35 | heisenberg kernel: WARNING: CPU: 0 PID: 7137 at fs/btrfs/root-tree.c:136 btrfs_update_root+0x22b/0x320 [btrfs] | |
36 | (...) | |
37 | heisenberg kernel: CPU: 0 PID: 7137 Comm: btrfs-transacti Not tainted 4.19.0-4-amd64 #1 Debian 4.19.28-2 | |
38 | heisenberg kernel: Hardware name: FUJITSU LIFEBOOK U757/FJNB2A5, BIOS Version 1.21 03/19/2018 | |
39 | heisenberg kernel: RIP: 0010:btrfs_update_root+0x22b/0x320 [btrfs] | |
40 | (...) | |
41 | heisenberg kernel: RSP: 0018:ffffb5448828bd40 EFLAGS: 00010286 | |
42 | heisenberg kernel: RAX: 0000000000000000 RBX: ffff8ed56bccef50 RCX: 0000000000000006 | |
43 | heisenberg kernel: RDX: 0000000000000007 RSI: 0000000000000092 RDI: ffff8ed6bda166a0 | |
44 | heisenberg kernel: RBP: 00000000ffffffe4 R08: 00000000000003df R09: 0000000000000007 | |
45 | heisenberg kernel: R10: 0000000000000000 R11: 0000000000000001 R12: ffff8ed63396a078 | |
46 | heisenberg kernel: R13: ffff8ed092d7c800 R14: ffff8ed64f5db028 R15: ffff8ed6bd03d068 | |
47 | heisenberg kernel: FS: 0000000000000000(0000) GS:ffff8ed6bda00000(0000) knlGS:0000000000000000 | |
48 | heisenberg kernel: CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 | |
49 | heisenberg kernel: CR2: 00007f46f75f8000 CR3: 0000000310a0a002 CR4: 00000000003606f0 | |
50 | heisenberg kernel: DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 | |
51 | heisenberg kernel: DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 | |
52 | heisenberg kernel: Call Trace: | |
53 | heisenberg kernel: commit_fs_roots+0x166/0x1d0 [btrfs] | |
54 | heisenberg kernel: ? _cond_resched+0x15/0x30 | |
55 | heisenberg kernel: ? btrfs_run_delayed_refs+0xac/0x180 [btrfs] | |
56 | heisenberg kernel: btrfs_commit_transaction+0x2bd/0x870 [btrfs] | |
57 | heisenberg kernel: ? start_transaction+0x9d/0x3f0 [btrfs] | |
58 | heisenberg kernel: transaction_kthread+0x147/0x180 [btrfs] | |
59 | heisenberg kernel: ? btrfs_cleanup_transaction+0x530/0x530 [btrfs] | |
60 | heisenberg kernel: kthread+0x112/0x130 | |
61 | heisenberg kernel: ? kthread_bind+0x30/0x30 | |
62 | heisenberg kernel: ret_from_fork+0x35/0x40 | |
63 | heisenberg kernel: ---[ end trace 05de912e30e012d9 ]--- | |
64 | ||
65 | So fix that by using the attach API, which does not create a transaction | |
66 | when there is currently no running transaction. | |
67 | ||
68 | [1] https://lore.kernel.org/linux-btrfs/b2a668d7124f1d3e410367f587926f622b3f03a4.camel@scientia.net/ | |
69 | ||
70 | Reported-by: Zygo Blaxell <ce3g8jdj@umail.furryterror.org> | |
71 | CC: stable@vger.kernel.org # 4.4+ | |
72 | Signed-off-by: Filipe Manana <fdmanana@suse.com> | |
73 | Reviewed-by: David Sterba <dsterba@suse.com> | |
74 | Signed-off-by: David Sterba <dsterba@suse.com> | |
75 | Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> | |
76 | ||
77 | --- | |
78 | fs/btrfs/backref.c | 18 ++++++++++++------ | |
79 | 1 file changed, 12 insertions(+), 6 deletions(-) | |
80 | ||
81 | --- a/fs/btrfs/backref.c | |
82 | +++ b/fs/btrfs/backref.c | |
83 | @@ -1685,13 +1685,19 @@ int iterate_extent_inodes(struct btrfs_f | |
84 | extent_item_objectid); | |
85 | ||
86 | if (!search_commit_root) { | |
87 | - trans = btrfs_join_transaction(fs_info->extent_root); | |
88 | - if (IS_ERR(trans)) | |
89 | - return PTR_ERR(trans); | |
90 | + trans = btrfs_attach_transaction(fs_info->extent_root); | |
91 | + if (IS_ERR(trans)) { | |
92 | + if (PTR_ERR(trans) != -ENOENT && | |
93 | + PTR_ERR(trans) != -EROFS) | |
94 | + return PTR_ERR(trans); | |
95 | + trans = NULL; | |
96 | + } | |
97 | + } | |
98 | + | |
99 | + if (trans) | |
100 | btrfs_get_tree_mod_seq(fs_info, &tree_mod_seq_elem); | |
101 | - } else { | |
102 | + else | |
103 | down_read(&fs_info->commit_root_sem); | |
104 | - } | |
105 | ||
106 | ret = btrfs_find_all_leafs(trans, fs_info, extent_item_objectid, | |
107 | tree_mod_seq_elem.seq, &refs, | |
108 | @@ -1721,7 +1727,7 @@ int iterate_extent_inodes(struct btrfs_f | |
109 | ||
110 | free_leaf_list(refs); | |
111 | out: | |
112 | - if (!search_commit_root) { | |
113 | + if (trans) { | |
114 | btrfs_put_tree_mod_seq(fs_info, &tree_mod_seq_elem); | |
115 | btrfs_end_transaction(trans, fs_info->extent_root); | |
116 | } else { |