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BUG: KCSAN: data-race in ext4_has_free_clusters / percpu_counter_add_batch

write to 0xffff88812a641158 of 8 bytes by task 26728 on cpu 1:
 percpu_counter_add_batch+0xca/0x150 lib/percpu_counter.c:91
 percpu_counter_add include/linux/percpu_counter.h:55 [inline]
 ext4_claim_free_clusters+0x68/0x90 fs/ext4/balloc.c:602
 ext4_da_reserve_space+0x102/0x280 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+0x87f/0xa60 fs/ext4/inode.c:1811
 ext4_block_write_begin+0x33e/0xba0 fs/ext4/inode.c:1054
 ext4_da_write_begin+0x208/0x840 fs/ext4/inode.c:2997
 generic_perform_write+0x136/0x320 mm/filemap.c:3287
 ext4_buffered_write_iter+0x143/0x290 fs/ext4/file.c:270
 ext4_file_write_iter+0xfa/0xd70 fs/ext4/file.c:642
 call_write_iter include/linux/fs.h:1901 [inline]
 new_sync_write+0x388/0x4a0 fs/read_write.c:483
 __vfs_write+0xb1/0xc0 fs/read_write.c:496
 vfs_write fs/read_write.c:558 [inline]
 vfs_write+0x18a/0x390 fs/read_write.c:542
 ksys_write+0xd5/0x1b0 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+0x4c/0x60 fs/read_write.c:620
 do_syscall_64+0xcc/0x3a0 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff88812a641158 of 8 bytes by task 27143 on cpu 0:
 ext4_has_free_clusters+0x61/0x320 fs/ext4/balloc.c:558
 ext4_claim_free_clusters+0x2e/0x90 fs/ext4/balloc.c:601
 ext4_da_reserve_space+0x102/0x280 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+0x87f/0xa60 fs/ext4/inode.c:1811
 ext4_block_write_begin+0x33e/0xba0 fs/ext4/inode.c:1054
 ext4_da_write_begin+0x208/0x840 fs/ext4/inode.c:2997
 generic_perform_write+0x136/0x320 mm/filemap.c:3287
 ext4_buffered_write_iter+0x143/0x290 fs/ext4/file.c:270
 ext4_file_write_iter+0xfa/0xd70 fs/ext4/file.c:642
 call_write_iter include/linux/fs.h:1901 [inline]
 new_sync_write+0x388/0x4a0 fs/read_write.c:483
 __vfs_write+0xb1/0xc0 fs/read_write.c:496
 vfs_write fs/read_write.c:558 [inline]
 vfs_write+0x18a/0x390 fs/read_write.c:542
 ksys_write+0xd5/0x1b0 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+0x4c/0x60 fs/read_write.c:620
 do_syscall_64+0xcc/0x3a0 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 27143 Comm: syz-executor.4 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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