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BUG: KCSAN: data-race in ext4_nonda_switch / percpu_counter_add_batch

write to 0xffff88812655f0e0 of 8 bytes by task 8555 on cpu 0:
 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
 mpage_map_one_extent fs/ext4/inode.c:2468 [inline]
 mpage_map_and_submit_extent fs/ext4/inode.c:2517 [inline]
 ext4_writepages+0x136e/0x2300 fs/ext4/inode.c:2869
 do_writepages+0x6b/0x170 mm/page-writeback.c:2344
 __filemap_fdatawrite_range+0x1c5/0x230 mm/filemap.c:420
 file_write_and_wait_range+0xfd/0x160 mm/filemap.c:781
 __generic_file_fsync+0x59/0x190 fs/libfs.c:1000
 ext4_sync_file+0x48e/0xb00 fs/ext4/fsync.c:120
 vfs_fsync_range+0x82/0x150 fs/sync.c:197
 generic_write_sync include/linux/fs.h:2853 [inline]
 ext4_file_write_iter+0x45b/0xa00 fs/ext4/file.c:279
 call_write_iter include/linux/fs.h:1895 [inline]
 do_iter_readv_writev+0x487/0x5b0 fs/read_write.c:693

read to 0xffff88812655f0e0 of 8 bytes by task 8564 on cpu 1:
 ext4_nonda_switch+0x3d/0x140 fs/ext4/inode.c:2988
 ext4_da_write_begin+0xc5/0x7e0 fs/ext4/inode.c:3036
 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]
 do_iter_readv_writev+0x487/0x5b0 fs/read_write.c:693
 do_iter_write fs/read_write.c:970 [inline]
 do_iter_write+0x13b/0x3c0 fs/read_write.c:951
 vfs_iter_write+0x5c/0x80 fs/read_write.c:983
 iter_file_splice_write+0x4c0/0x7f0 fs/splice.c:746
 do_splice_from fs/splice.c:848 [inline]
 direct_splice_actor+0xa0/0xc0 fs/splice.c:1020
 splice_direct_to_actor+0x215/0x510 fs/splice.c:975
 do_splice_direct+0x161/0x1e0 fs/splice.c:1063
 do_sendfile+0x384/0x7f0 fs/read_write.c:1464

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 8564 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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