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BUG: KCSAN: data-race in find_group_orlov / percpu_counter_add_batch

read to 0xffff888126bfc8e0 of 8 bytes by task 19748 on cpu 0:
 find_group_orlov+0x15c/0x8d0 fs/ext4/ialloc.c:443
 __ext4_new_inode+0xab5/0x2ec0 fs/ext4/ialloc.c:871
 ext4_mkdir+0x289/0x820 fs/ext4/namei.c:2763
 vfs_mkdir+0x283/0x390 fs/namei.c:3807
 do_mkdirat+0x1ac/0x1f0 fs/namei.c:3830
 __do_sys_mkdir fs/namei.c:3846 [inline]
 __se_sys_mkdir fs/namei.c:3844 [inline]
 __x64_sys_mkdir+0x40/0x50 fs/namei.c:3844
 do_syscall_64+0xcc/0x370 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

write to 0xffff888126bfc8e0 of 8 bytes by task 19747 on cpu 1:
 percpu_counter_add_batch+0xca/0x150 lib/percpu_counter.c:91
 percpu_counter_add include/linux/percpu_counter.h:55 [inline]
 percpu_counter_sub include/linux/percpu_counter.h:189 [inline]
 ext4_mb_mark_diskspace_used+0x525/0x9d0 fs/ext4/mballoc.c:3010
 ext4_mb_new_blocks+0x6fc/0x1de0 fs/ext4/mballoc.c:4556
 ext4_ext_map_blocks+0x1c1e/0x2330 fs/ext4/extents.c:4460
 ext4_map_blocks+0x23a/0xfa0 fs/ext4/inode.c:640
 ext4_alloc_file_blocks+0x1bd/0x6c0 fs/ext4/extents.c:4649
 ext4_fallocate+0x507/0x13d0 fs/ext4/extents.c:4934
 vfs_fallocate+0x3be/0x650 fs/open.c:309
 ioctl_preallocate+0x126/0x180 fs/ioctl.c:490
 file_ioctl fs/ioctl.c:506 [inline]
 do_vfs_ioctl+0xbd2/0xc60 fs/ioctl.c:696
 ksys_ioctl+0xbd/0xe0 fs/ioctl.c:713
 __do_sys_ioctl fs/ioctl.c:720 [inline]
 __se_sys_ioctl fs/ioctl.c:718 [inline]
 __x64_sys_ioctl+0x4c/0x60 fs/ioctl.c:718
 do_syscall_64+0xcc/0x370 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 19747 Comm: syz-executor.5 Not tainted 5.4.0-rc6+ #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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