Btrfs: fix qgroups sanity test crash or hang

Often when running the qgroups sanity test, a crash or a hang happened.
This is because the extent buffer the test uses for the root node doe

Btrfs: fix qgroups sanity test crash or hang

Often when running the qgroups sanity test, a crash or a hang happened.
This is because the extent buffer the test uses for the root node doesn't
have an header level explicitly set, making it have a random level value.
This is a problem when it's not zero for the btrfs_search_slot() calls
the test ends up doing, resulting in crashes or hangs such as the following:

[ 6454.127192] Btrfs loaded, debug=on, assert=on, integrity-checker=on
(...)
[ 6454.127760] BTRFS: selftest: Running qgroup tests
[ 6454.127964] BTRFS: selftest: Running test_test_no_shared_qgroup
[ 6454.127966] BTRFS: selftest: Qgroup basic add
[ 6480.152005] BUG: soft lockup - CPU#0 stuck for 23s! [modprobe:5383]
[ 6480.152005] Modules linked in: btrfs(+) xor raid6_pq binfmt_misc nfsd auth_rpcgss oid_registry nfs_acl nfs lockd fscache sunrpc i2c_piix4 i2c_core pcspkr evbug psmouse serio_raw e1000 [last unloaded: btrfs]
[ 6480.152005] irq event stamp: 188448
[ 6480.152005] hardirqs last enabled at (188447): [<ffffffff8168ef5c>] restore_args+0x0/0x30
[ 6480.152005] hardirqs last disabled at (188448): [<ffffffff81698e6a>] apic_timer_interrupt+0x6a/0x80
[ 6480.152005] softirqs last enabled at (188446): [<ffffffff810516cf>] __do_softirq+0x1cf/0x450
[ 6480.152005] softirqs last disabled at (188441): [<ffffffff81051c25>] irq_exit+0xb5/0xc0
[ 6480.152005] CPU: 0 PID: 5383 Comm: modprobe Not tainted 3.15.0-rc8-fdm-btrfs-next-33+ #4
[ 6480.152005] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
[ 6480.152005] task: ffff8802146125a0 ti: ffff8800d0d00000 task.ti: ffff8800d0d00000
[ 6480.152005] RIP: 0010:[<ffffffff81349a63>] [<ffffffff81349a63>] __write_lock_failed+0x13/0x20
[ 6480.152005] RSP: 0018:ffff8800d0d038e8 EFLAGS: 00000287
[ 6480.152005] RAX: 0000000000000000 RBX: ffffffff8168ef5c RCX: 000005deb8525852
[ 6480.152005] RDX: 0000000000000000 RSI: 0000000000001d45 RDI: ffff8802105000b8
[ 6480.152005] RBP: ffff8800d0d038e8 R08: fffffe12710f63db R09: ffffffffa03196fb
[ 6480.152005] R10: ffff8802146125a0 R11: ffff880214612e28 R12: ffff8800d0d03858
[ 6480.152005] R13: 0000000000000000 R14: ffff8800d0d00000 R15: ffff8802146125a0
[ 6480.152005] FS: 00007f14ff804700(0000) GS:ffff880215e00000(0000) knlGS:0000000000000000
[ 6480.152005] CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b
[ 6480.152005] CR2: 00007fff4df0dac8 CR3: 00000000d1796000 CR4: 00000000000006f0
[ 6480.152005] Stack:
[ 6480.152005] ffff8800d0d03908 ffffffff810ae967 0000000000000001 ffff8802105000b8
[ 6480.152005] ffff8800d0d03938 ffffffff8168e57e ffffffffa0319c16 0000000000000007
[ 6480.152005] ffff880210500000 ffff880210500100 ffff8800d0d039b8 ffffffffa0319c16
[ 6480.152005] Call Trace:
[ 6480.152005] [<ffffffff810ae967>] do_raw_write_lock+0x47/0xa0
[ 6480.152005] [<ffffffff8168e57e>] _raw_write_lock+0x5e/0x80
[ 6480.152005] [<ffffffffa0319c16>] ? btrfs_tree_lock+0x116/0x270 [btrfs]
[ 6480.152005] [<ffffffffa0319c16>] btrfs_tree_lock+0x116/0x270 [btrfs]
[ 6480.152005] [<ffffffffa02b2acb>] btrfs_lock_root_node+0x3b/0x50 [btrfs]
[ 6480.152005] [<ffffffffa02b81a6>] btrfs_search_slot+0x916/0xa20 [btrfs]
[ 6480.152005] [<ffffffff811a727f>] ? create_object+0x23f/0x300
[ 6480.152005] [<ffffffffa02b9958>] btrfs_insert_empty_items+0x78/0xd0 [btrfs]
[ 6480.152005] [<ffffffffa036041a>] insert_normal_tree_ref.constprop.4+0xa2/0x19a [btrfs]
[ 6480.152005] [<ffffffffa03605c3>] test_no_shared_qgroup+0xb1/0x1ca [btrfs]
[ 6480.152005] [<ffffffff8108cad6>] ? local_clock+0x16/0x30
[ 6480.152005] [<ffffffffa035ef8e>] btrfs_test_qgroups+0x1ae/0x1d7 [btrfs]
[ 6480.152005] [<ffffffffa03a69d2>] ? ftrace_define_fields_btrfs_space_reservation+0xfd/0xfd [btrfs]
[ 6480.152005] [<ffffffffa03a6a86>] init_btrfs_fs+0xb4/0x153 [btrfs]
[ 6480.152005] [<ffffffff81000352>] do_one_initcall+0x102/0x150
[ 6480.152005] [<ffffffff8103d223>] ? set_memory_nx+0x43/0x50
[ 6480.152005] [<ffffffff81682668>] ? set_section_ro_nx+0x6d/0x74
[ 6480.152005] [<ffffffff810d91cc>] load_module+0x1cdc/0x2630
(...)

Therefore initialize the extent buffer as an empty leaf (level 0).

Issue easy to reproduce when btrfs is built as a module via:

$ for ((i = 1; i <= 1000000; i++)); do rmmod btrfs; modprobe btrfs; done

Signed-off-by: Filipe David Borba Manana <fdmanana@gmail.com>
Signed-off-by: Chris Mason <clm@fb.com>

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Btrfs: add sanity tests for new qgroup accounting code

This exercises the various parts of the new qgroup accounting code. We do some
basic stuff and do some things with the shared refs

Btrfs: add sanity tests for new qgroup accounting code

This exercises the various parts of the new qgroup accounting code. We do some
basic stuff and do some things with the shared refs to make sure all that code
works. I had to add a bunch of infrastructure because I needed to be able to
insert items into a fake tree without having to do all the hard work myself,
hopefully this will be usefull in the future. Thanks,

Signed-off-by: Josef Bacik <jbacik@fb.com>
Signed-off-by: Chris Mason <clm@fb.com>

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