3.15 btrfs free space cache oops

[Daniel J Blueman]

When running MonetDB against a BTRFS RAID-0 set over 4 SSDs [1] on
3.15.5, we see io_ctl have a bad address of 0x200000, causing a fatal
pagefault in memcpy():

(gdb) list *(__btrfs_write_out_cache+0x3e4)
0xffffffff81365984 is in __btrfs_write_out_cache
(fs/btrfs/free-space-cache.c:521).
516            if (io_ctl->index >= io_ctl->num_pages)
517                return -ENOSPC;
518            io_ctl_map_page(io_ctl, 0);
519        }
520
521        memcpy(io_ctl->cur, bitmap, PAGE_CACHE_SIZE);
522        io_ctl_set_crc(io_ctl, io_ctl->index - 1);
523        if (io_ctl->index < io_ctl->num_pages)
524            io_ctl_map_page(io_ctl, 0);
525        return 0;

I can try to reproduce it if more data is useful?

Thanks,
  Daniel

-- [1]

mkfs.btrfs -f -m raid0 -d raid0 -n 16k -l 16k -O skinny-metadata
/dev/sda2 /dev/sdc2 /dev/sdb2 /dev/sdd2
mount /dev/sda2 /scratch -o noatime,discard,nodatasum,nobarrier,ssd_spread

-- [2]

BUG: unable to handle kernel paging request at 0000000000200000
IP: [<ffffffff8135a374>] __btrfs_write_out_cache+0x3e4/0x8e0
PGD 3bca02c067 PUD 3bcf5fb067 PMD 0
Oops: 0000 [#1] SMP
Modules linked in:
CPU: 34 PID: 46645 Comm: mserver5 Not tainted 3.15.5-server #7
Hardware name: Dell Inc. PowerEdge R815/0W13NR, BIOS 3.1.1 [1.1.54] 10/16/2013
task: ffff880a8c7234f0 ti: ffff8809aefcc000 task.ti: ffff8809aefcc000
RIP: 0010:[<ffffffff8135a374>] [<ffffffff8135a374>]
__btrfs_write_out_cache+0x3e4/0x8e0
RSP: 0018:ffff8809aefcfc40 EFLAGS: 00010246
RAX: 0000004fb9321000 RBX: ffff8809aefcfca8 RCX: 0000000000000200
RDX: 0000000000001000 RSI: 0000000000200000 RDI: ffff884fb9321000
RBP: ffff8809aefcfd48 R08: 0000000000000200 R09: 0000000000000000
R10: 0000000000000000 R11: ffff884fb9320ffc R12: ffff8831e3303740
R13: ffff880100579970 R14: ffff880bb38061c0 R15: 0000000000200000
FS: 00007fb9447ed700(0000) GS:ffff884bbfc80000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000200000 CR3: 000000329b71c000 CR4: 00000000000407e0
Stack:
 ffff8809aefcfc90 0000000000000011 0000000e00000000 ffff884fbbc2c870
 ffff880bb38061c0 ffff8809aefcfc90 ffff880bb3806058 ffff880b000002ec
 ffff883bcd523800 ffff8833d338f2c0 ffff88476b1eb4e0 000000b890cde000
Call Trace:
 [<ffffffff81a75b4b>] ? _raw_spin_lock+0xb/0x20
 [<ffffffff8135c0e1>] btrfs_write_out_cache+0xb1/0xf0
 [<ffffffff8130be0b>] btrfs_write_dirty_block_groups+0x58b/0x670
 [<ffffffff813199c5>] commit_cowonly_roots+0x195/0x250
 [<ffffffff8131b92f>] btrfs_commit_transaction+0x41f/0x9b0
 [<ffffffff81358e85>] ? btrfs_log_dentry_safe+0x55/0x70
 [<ffffffff8132b6b2>] btrfs_sync_file+0x182/0x2a0
 [<ffffffff8114a450>] do_fsync+0x50/0x80
 [<ffffffff8114a6de>] SyS_fdatasync+0xe/0x20
 [<ffffffff81a766e6>] system_call_fastpath+0x1a/0x1f
Code: ff 4d 89 fc 49 89 c7 e9 ab 00 00 00 0f 1f 00 40 f6 c7 02 0f 85
fe 00 00 00 40 f6 c7 04 0f 85 14 01 00 00 89 d1 c1 e9 03 f6 c2 04 <f3>
48 a5 74 09 8b 0e 89 0f b9 04 00 00 00 f6 c2 02 74 0e 44 0f
RIP [<ffffffff8135a374>] __btrfs_write_out_cache+0x3e4/0x8e0
 RSP <ffff8809aefcfc40>
CR2: 0000000000200000
-- 
Daniel J Blueman
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