BTRFS info (device loop4): enabling ssd optimizations
BTRFS info (device loop4): creating free space tree
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BUG: KCSAN: data-race in caching_thread / find_free_extent

write to 0xffff88809309b8a4 of 4 bytes by task 7 on cpu 1:
 caching_thread+0x6ac/0x7e0 fs/btrfs/block-group.c:649
 btrfs_work_helper+0x1e2/0x3c0 fs/btrfs/async-thread.c:318
 process_one_work+0x3e1/0x9a0 kernel/workqueue.c:2269
 worker_thread+0x665/0xbe0 kernel/workqueue.c:2415
 kthread+0x20d/0x230 kernel/kthread.c:292
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294

read to 0xffff88809309b8a4 of 4 bytes by task 20669 on cpu 0:
 find_free_extent+0xf21/0x1a70 fs/btrfs/extent-tree.c:4072
 btrfs_reserve_extent+0x118/0x2c0 fs/btrfs/extent-tree.c:4206
 btrfs_alloc_tree_block+0x101/0x800 fs/btrfs/extent-tree.c:4603
 btrfs_create_tree+0x110/0x4a0 fs/btrfs/disk-io.c:1212
 btrfs_create_free_space_tree+0x66/0x7b0 fs/btrfs/free-space-tree.c:1155
 open_ctree+0x23f8/0x259c fs/btrfs/disk-io.c:3330
 btrfs_fill_super fs/btrfs/super.c:1316 [inline]
 btrfs_mount_root+0x742/0x830 fs/btrfs/super.c:1672
 legacy_get_tree+0x70/0xc0 fs/fs_context.c:592
 vfs_get_tree+0x4d/0x1a0 fs/super.c:1547
 fc_mount fs/namespace.c:978 [inline]
 vfs_kern_mount+0xc6/0x130 fs/namespace.c:1008
 btrfs_mount+0x27b/0x790 fs/btrfs/super.c:1732
 legacy_get_tree+0x70/0xc0 fs/fs_context.c:592
 vfs_get_tree+0x4d/0x1a0 fs/super.c:1547
 do_new_mount fs/namespace.c:2875 [inline]
 path_mount+0x118d/0x1c70 fs/namespace.c:3192
 do_mount fs/namespace.c:3205 [inline]
 __do_sys_mount fs/namespace.c:3413 [inline]
 __se_sys_mount+0x126/0x180 fs/namespace.c:3390
 __x64_sys_mount+0x63/0x70 fs/namespace.c:3390
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 20669 Comm: syz-executor.4 Not tainted 5.9.0-rc5-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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