[PATCH] Btrfs: do not release delalloc space until after we end the transaction

[Josef Bacik <josef@redhat.com>]

There have been many sporadic reports of the following panic

------------[ cut here ]------------
kernel BUG at fs/btrfs/extent-tree.c:5498!
invalid opcode: 0000 [#1] PREEMPT SMP
last sysfs file: /sys/devices/system/cpu/cpu7/cache/index2/shared_cpu_map
CPU 7
Modules linked in: btrfs zlib_deflate libcrc32c netconsole configfs ipt_MASQUERADE iptable_nat nf_nat bridge stp llc sunrpc cpufreq_ondemand acpi_cpufreq freq_table mperf xt_physdev ip6t_REJECT nf_conntrack_ipv6 nf_defrag_ipv6 ip6table_filter ip6_tables ipv6 dm_multipath kvm uinput snd_hda_codec_realtek snd_hda_intel snd_hda_codec snd_hwdep snd_seq snd_seq_device snd_pcm snd_timer snd hp_wmi i5400_edac sparse_keymap iTCO_wdt rfkill edac_core tg3 shpchp iTCO_vendor_support soundcore wmi floppy snd_page_alloc pcspkr i5k_amb [last unloaded: btrfs]

Pid: 28504, comm: btrfs-endio-wri Tainted: G        W   2.6.39-rc2+ #35 Hewlett-Packard HP xw6600 Workstation/0A9Ch
RIP: 0010:[<ffffffffa044ec34>]  [<ffffffffa044ec34>] alloc_reserved_file_extent+0x9a/0x1e5 [btrfs]
RSP: 0018:ffff88000b4319f0  EFLAGS: 00010286
RAX: 00000000ffffffe4 RBX: ffff880009fdc438 RCX: ffff880020c216d0
RDX: ffff88000b4318c0 RSI: 00000000000000d5 RDI: 0000000000000000
RBP: ffff88000b431a70 R08: 00000000ffffffe4 R09: ffff880020c216d0
R10: 0000000000000001 R11: ffff88000b431b10 R12: ffff88000b431b10
R13: 00000000000000b2 R14: 0000000000000000 R15: ffff88002225f2f8
FS:  0000000000000000(0000) GS:ffff88003e400000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
CR2: 0000003738ca6940 CR3: 000000002a39a000 CR4: 00000000000006e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
Process btrfs-endio-wri (pid: 28504, threadinfo ffff88000b430000, task ffff880032278000)
Stack:
 0000000000000001 ffff88002a920000 ffff88000000001d 000000000000038d
 0000000000000000 0000000000000005 ffff88003aa38000 ffffffff81481012
 ffff88000c3bb480 ffff8800241d01c8 ffff88000b431a60 ffff880031a040a8
Call Trace:
 [<ffffffff81481012>] ? sub_preempt_count+0x97/0xaa
 [<ffffffffa044f92e>] run_clustered_refs+0x61b/0x700 [btrfs]
 [<ffffffff81480f89>] ? sub_preempt_count+0xe/0xaa
 [<ffffffffa0446ee9>] ? spin_lock+0xe/0x10 [btrfs]
 [<ffffffffa044fae4>] btrfs_run_delayed_refs+0xd1/0x1ab [btrfs]
 [<ffffffff8147dc1c>] ? _raw_spin_unlock+0x4a/0x57
 [<ffffffffa045af1b>] __btrfs_end_transaction+0x89/0x1ed [btrfs]
 [<ffffffffa045b0c2>] btrfs_end_transaction+0x15/0x17 [btrfs]
 [<ffffffffa0466932>] btrfs_finish_ordered_io+0x29c/0x2bf [btrfs]
 [<ffffffffa04669d6>] btrfs_writepage_end_io_hook+0x81/0x8d [btrfs]
 [<ffffffffa0477fd5>] end_bio_extent_writepage+0xae/0x159 [btrfs]
 [<ffffffff811457e3>] bio_endio+0x2d/0x2f
 [<ffffffffa0456c44>] end_workqueue_fn+0x111/0x120 [btrfs]
 [<ffffffffa0480a0e>] worker_loop+0x192/0x4d1 [btrfs]
 [<ffffffffa048087c>] ? btrfs_queue_worker+0x22c/0x22c [btrfs]
 [<ffffffff81068a69>] kthread+0xa0/0xa8
 [<ffffffff8107a847>] ? trace_hardirqs_on_caller+0x111/0x135
 [<ffffffff81485364>] kernel_thread_helper+0x4/0x10
 [<ffffffff8147e398>] ? retint_restore_args+0x13/0x13
 [<ffffffff810689c9>] ? __init_kthread_worker+0x5b/0x5b
 [<ffffffff81485360>] ? gs_change+0x13/0x13
Code: 44 8b 45 90 0f 84 58 01 00 00 80 88 88 00 00 00 08 41 83 c0 18 4c 89 e1 48 8b 72 20 4c 89 ff 48 89 c2 e8 1f b4 ff ff 85 c0 74 04 <0f> 0b eb fe 48 8b 03 48 89 45 c8 8b 73 40 48 89 c7 e8 bc 98 ff
RIP  [<ffffffffa044ec34>] alloc_reserved_file_extent+0x9a/0x1e5 [btrfs]
 RSP <ffff88000b4319f0>
---[ end trace 81d1c68cb00af83e ]---

This is because we have been releasing the delalloc bytes before ending the
transaction.  However the way we make allocations, any updates to the
extent_tree are delayed and then run when the transaction runs, so we still have
plenty of space that we need to use.  So instead release the delalloc bytes
_after_ we end the transaction so that we don't get this false ENOSPC.  Thanks,

Signed-off-by: Josef Bacik <josef@redhat.com>
---
 fs/btrfs/inode.c |    8 ++++++--
 1 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index ade00e7..b1e5b11 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -1783,9 +1783,13 @@ out:
 		if (trans)
 			btrfs_end_transaction_nolock(trans, root);
 	} else {
-		btrfs_delalloc_release_metadata(inode, ordered_extent->len);
 		if (trans)
 			btrfs_end_transaction(trans, root);
+		/*
+		 * Release after the transaction ends so it covers the delayed
+		 * ref updates
+		 */
+		btrfs_delalloc_release_metadata(inode, ordered_extent->len);
 	}
 
 	/* once for us */
@@ -5897,8 +5901,8 @@ out_unlock:
 			     ordered->file_offset + ordered->len - 1,
 			     &cached_state, GFP_NOFS);
 out:
-	btrfs_delalloc_release_metadata(inode, ordered->len);
 	btrfs_end_transaction(trans, root);
+	btrfs_delalloc_release_metadata(inode, ordered->len);
 	ordered_offset = ordered->file_offset + ordered->len;
 	btrfs_put_ordered_extent(ordered);
 	btrfs_put_ordered_extent(ordered);
-- 
1.7.2.3