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BUG: KCSAN: data-race in ext4_nonda_switch / percpu_counter_add_batch

read to 0xffff888218707958 of 8 bytes by task 27391 on cpu 1:
 ext4_nonda_switch+0x5a/0x140 fs/ext4/inode.c:2990
 ext4_page_mkwrite+0x748/0xce0 fs/ext4/inode.c:6215
 do_page_mkwrite+0x100/0x210 mm/memory.c:2208
 do_shared_fault mm/memory.c:3554 [inline]
 do_fault mm/memory.c:3622 [inline]
 handle_pte_fault mm/memory.c:3849 [inline]
 __handle_mm_fault+0x2099/0x2cb0 mm/memory.c:3973
 handle_mm_fault+0x21b/0x530 mm/memory.c:4010
 do_user_addr_fault arch/x86/mm/fault.c:1441 [inline]
 __do_page_fault+0x3fb/0x9e0 arch/x86/mm/fault.c:1506
 do_page_fault+0x54/0x233 arch/x86/mm/fault.c:1530
 page_fault+0x34/0x40 arch/x86/entry/entry_64.S:1202

write to 0xffff888218707958 of 8 bytes by task 27389 on cpu 0:
 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:599
 ext4_da_reserve_space+0x102/0x280 fs/ext4/inode.c:1612
 ext4_insert_delayed_block fs/ext4/inode.c:1780 [inline]
 ext4_da_map_blocks fs/ext4/inode.c:1895 [inline]
 ext4_da_get_block_prep+0x87f/0xa60 fs/ext4/inode.c:1959
 ext4_block_write_begin+0x33e/0xba0 fs/ext4/inode.c:1202
 ext4_da_write_begin+0x1da/0x7e0 fs/ext4/inode.c:3094
 generic_perform_write+0x136/0x320 mm/filemap.c:3304
 __generic_file_write_iter+0x251/0x380 mm/filemap.c:3433
 ext4_file_write_iter+0x1bd/0xa00 fs/ext4/file.c:268
 call_write_iter include/linux/fs.h:1895 [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

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 27389 Comm: syz-executor.2 Not tainted 5.4.0-rc3+ #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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