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BUG: KCSAN: data-race in ext4_has_free_clusters / percpu_counter_add_batch

write to 0xffff8881290ca958 of 8 bytes by task 9519 on cpu 1:
 percpu_counter_add_batch+0xbc/0x140 lib/percpu_counter.c:91
 percpu_counter_add include/linux/percpu_counter.h:55 [inline]
 ext4_claim_free_clusters+0x64/0x80 fs/ext4/balloc.c:602
 ext4_da_reserve_space+0xf8/0x270 fs/ext4/inode.c:1464
 ext4_insert_delayed_block fs/ext4/inode.c:1632 [inline]
 ext4_da_map_blocks fs/ext4/inode.c:1747 [inline]
 ext4_da_get_block_prep+0x87e/0xa50 fs/ext4/inode.c:1811
 ext4_block_write_begin+0x336/0xbd0 fs/ext4/inode.c:1054
 ext4_da_write_begin+0x220/0x860 fs/ext4/inode.c:2997
 generic_perform_write+0x13a/0x320 mm/filemap.c:3287
 ext4_buffered_write_iter+0x14e/0x280 fs/ext4/file.c:270
 ext4_file_write_iter+0xf4/0xd30 fs/ext4/file.c:642
 call_write_iter include/linux/fs.h:1901 [inline]
 new_sync_write+0x303/0x400 fs/read_write.c:483
 __vfs_write+0x9e/0xb0 fs/read_write.c:496
 vfs_write fs/read_write.c:558 [inline]
 vfs_write+0x189/0x380 fs/read_write.c:542
 ksys_write+0xc5/0x1a0 fs/read_write.c:611
 __do_sys_write fs/read_write.c:623 [inline]
 __se_sys_write fs/read_write.c:620 [inline]
 __x64_sys_write+0x49/0x60 fs/read_write.c:620
 do_syscall_64+0xc7/0x390 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff8881290ca958 of 8 bytes by task 9511 on cpu 0:
 ext4_has_free_clusters+0x61/0x310 fs/ext4/balloc.c:558
 ext4_claim_free_clusters+0x2c/0x80 fs/ext4/balloc.c:601
 ext4_da_reserve_space+0xf8/0x270 fs/ext4/inode.c:1464
 ext4_insert_delayed_block fs/ext4/inode.c:1632 [inline]
 ext4_da_map_blocks fs/ext4/inode.c:1747 [inline]
 ext4_da_get_block_prep+0x87e/0xa50 fs/ext4/inode.c:1811
 ext4_block_write_begin+0x336/0xbd0 fs/ext4/inode.c:1054
 ext4_da_write_begin+0x220/0x860 fs/ext4/inode.c:2997
 generic_perform_write+0x13a/0x320 mm/filemap.c:3287
 ext4_buffered_write_iter+0x14e/0x280 fs/ext4/file.c:270
 ext4_file_write_iter+0xf4/0xd30 fs/ext4/file.c:642
 call_write_iter include/linux/fs.h:1901 [inline]
 new_sync_write+0x303/0x400 fs/read_write.c:483
 __vfs_write+0x9e/0xb0 fs/read_write.c:496
 vfs_write fs/read_write.c:558 [inline]
 vfs_write+0x189/0x380 fs/read_write.c:542
 ksys_write+0xc5/0x1a0 fs/read_write.c:611
 __do_sys_write fs/read_write.c:623 [inline]
 __se_sys_write fs/read_write.c:620 [inline]
 __x64_sys_write+0x49/0x60 fs/read_write.c:620
 do_syscall_64+0xc7/0x390 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 9511 Comm: syz-executor.3 Not tainted 5.6.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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