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BUG: KCSAN: data-race in ext4_has_free_clusters / percpu_counter_add_batch

write to 0xffff88821867d158 of 8 bytes by task 15532 on cpu 0:
 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]
 do_iter_readv_writev+0x4a7/0x5d0 fs/read_write.c:693
 do_iter_write fs/read_write.c:998 [inline]
 do_iter_write+0x137/0x3a0 fs/read_write.c:979
 vfs_writev+0x118/0x1c0 fs/read_write.c:1071
 do_writev+0xd9/0x240 fs/read_write.c:1114
 __do_sys_writev fs/read_write.c:1187 [inline]
 __se_sys_writev fs/read_write.c:1184 [inline]
 __x64_sys_writev+0x4b/0x60 fs/read_write.c:1184
 do_syscall_64+0xc7/0x390 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff88821867d158 of 8 bytes by task 15535 on cpu 1:
 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]
 do_iter_readv_writev+0x4a7/0x5d0 fs/read_write.c:693
 do_iter_write fs/read_write.c:998 [inline]
 do_iter_write+0x137/0x3a0 fs/read_write.c:979
 vfs_writev+0x118/0x1c0 fs/read_write.c:1071
 do_writev+0xd9/0x240 fs/read_write.c:1114
 __do_sys_writev fs/read_write.c:1187 [inline]
 __se_sys_writev fs/read_write.c:1184 [inline]
 __x64_sys_writev+0x4b/0x60 fs/read_write.c:1184
 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: 1 PID: 15535 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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