| From bfc61c36260ca990937539cd648ede3cd749bc10 Mon Sep 17 00:00:00 2001 |
| From: Filipe Manana <fdmanana@suse.com> |
| Date: Wed, 17 Apr 2019 11:30:30 +0100 |
| Subject: Btrfs: do not start a transaction at iterate_extent_inodes() |
| |
| From: Filipe Manana <fdmanana@suse.com> |
| |
| commit bfc61c36260ca990937539cd648ede3cd749bc10 upstream. |
| |
| When finding out which inodes have references on a particular extent, done |
| by backref.c:iterate_extent_inodes(), from the BTRFS_IOC_LOGICAL_INO (both |
| v1 and v2) ioctl and from scrub we use the transaction join API to grab a |
| reference on the currently running transaction, since in order to give |
| accurate results we need to inspect the delayed references of the currently |
| running transaction. |
| |
| However, if there is currently no running transaction, the join operation |
| will create a new transaction. This is inefficient as the transaction will |
| eventually be committed, doing unnecessary IO and introducing a potential |
| point of failure that will lead to a transaction abort due to -ENOSPC, as |
| recently reported [1]. |
| |
| That's because the join, creates the transaction but does not reserve any |
| space, so when attempting to update the root item of the root passed to |
| btrfs_join_transaction(), during the transaction commit, we can end up |
| failling with -ENOSPC. Users of a join operation are supposed to actually |
| do some filesystem changes and reserve space by some means, which is not |
| the case of iterate_extent_inodes(), it is a read-only operation for all |
| contextes from which it is called. |
| |
| The reported [1] -ENOSPC failure stack trace is the following: |
| |
| heisenberg kernel: ------------[ cut here ]------------ |
| heisenberg kernel: BTRFS: Transaction aborted (error -28) |
| heisenberg kernel: WARNING: CPU: 0 PID: 7137 at fs/btrfs/root-tree.c:136 btrfs_update_root+0x22b/0x320 [btrfs] |
| (...) |
| heisenberg kernel: CPU: 0 PID: 7137 Comm: btrfs-transacti Not tainted 4.19.0-4-amd64 #1 Debian 4.19.28-2 |
| heisenberg kernel: Hardware name: FUJITSU LIFEBOOK U757/FJNB2A5, BIOS Version 1.21 03/19/2018 |
| heisenberg kernel: RIP: 0010:btrfs_update_root+0x22b/0x320 [btrfs] |
| (...) |
| heisenberg kernel: RSP: 0018:ffffb5448828bd40 EFLAGS: 00010286 |
| heisenberg kernel: RAX: 0000000000000000 RBX: ffff8ed56bccef50 RCX: 0000000000000006 |
| heisenberg kernel: RDX: 0000000000000007 RSI: 0000000000000092 RDI: ffff8ed6bda166a0 |
| heisenberg kernel: RBP: 00000000ffffffe4 R08: 00000000000003df R09: 0000000000000007 |
| heisenberg kernel: R10: 0000000000000000 R11: 0000000000000001 R12: ffff8ed63396a078 |
| heisenberg kernel: R13: ffff8ed092d7c800 R14: ffff8ed64f5db028 R15: ffff8ed6bd03d068 |
| heisenberg kernel: FS: 0000000000000000(0000) GS:ffff8ed6bda00000(0000) knlGS:0000000000000000 |
| heisenberg kernel: CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 |
| heisenberg kernel: CR2: 00007f46f75f8000 CR3: 0000000310a0a002 CR4: 00000000003606f0 |
| heisenberg kernel: DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 |
| heisenberg kernel: DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 |
| heisenberg kernel: Call Trace: |
| heisenberg kernel: commit_fs_roots+0x166/0x1d0 [btrfs] |
| heisenberg kernel: ? _cond_resched+0x15/0x30 |
| heisenberg kernel: ? btrfs_run_delayed_refs+0xac/0x180 [btrfs] |
| heisenberg kernel: btrfs_commit_transaction+0x2bd/0x870 [btrfs] |
| heisenberg kernel: ? start_transaction+0x9d/0x3f0 [btrfs] |
| heisenberg kernel: transaction_kthread+0x147/0x180 [btrfs] |
| heisenberg kernel: ? btrfs_cleanup_transaction+0x530/0x530 [btrfs] |
| heisenberg kernel: kthread+0x112/0x130 |
| heisenberg kernel: ? kthread_bind+0x30/0x30 |
| heisenberg kernel: ret_from_fork+0x35/0x40 |
| heisenberg kernel: ---[ end trace 05de912e30e012d9 ]--- |
| |
| So fix that by using the attach API, which does not create a transaction |
| when there is currently no running transaction. |
| |
| [1] https://lore.kernel.org/linux-btrfs/b2a668d7124f1d3e410367f587926f622b3f03a4.camel@scientia.net/ |
| |
| Reported-by: Zygo Blaxell <ce3g8jdj@umail.furryterror.org> |
| CC: stable@vger.kernel.org # 4.4+ |
| Signed-off-by: Filipe Manana <fdmanana@suse.com> |
| Reviewed-by: David Sterba <dsterba@suse.com> |
| Signed-off-by: David Sterba <dsterba@suse.com> |
| Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
| |
| --- |
| fs/btrfs/backref.c | 18 ++++++++++++------ |
| 1 file changed, 12 insertions(+), 6 deletions(-) |
| |
| --- a/fs/btrfs/backref.c |
| +++ b/fs/btrfs/backref.c |
| @@ -1685,13 +1685,19 @@ int iterate_extent_inodes(struct btrfs_f |
| extent_item_objectid); |
| |
| if (!search_commit_root) { |
| - trans = btrfs_join_transaction(fs_info->extent_root); |
| - if (IS_ERR(trans)) |
| - return PTR_ERR(trans); |
| + trans = btrfs_attach_transaction(fs_info->extent_root); |
| + if (IS_ERR(trans)) { |
| + if (PTR_ERR(trans) != -ENOENT && |
| + PTR_ERR(trans) != -EROFS) |
| + return PTR_ERR(trans); |
| + trans = NULL; |
| + } |
| + } |
| + |
| + if (trans) |
| btrfs_get_tree_mod_seq(fs_info, &tree_mod_seq_elem); |
| - } else { |
| + else |
| down_read(&fs_info->commit_root_sem); |
| - } |
| |
| ret = btrfs_find_all_leafs(trans, fs_info, extent_item_objectid, |
| tree_mod_seq_elem.seq, &refs, |
| @@ -1721,7 +1727,7 @@ int iterate_extent_inodes(struct btrfs_f |
| |
| free_leaf_list(refs); |
| out: |
| - if (!search_commit_root) { |
| + if (trans) { |
| btrfs_put_tree_mod_seq(fs_info, &tree_mod_seq_elem); |
| btrfs_end_transaction(trans, fs_info->extent_root); |
| } else { |