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BUG: KCSAN: data-race in copy_page_to_iter / ext4_free_blocks

write to 0xffff888132adc000 of 8 bytes by task 7469 on cpu 1:
 instrument_write include/linux/instrumented.h:42 [inline]
 __clear_bit include/asm-generic/bitops/instrumented-non-atomic.h:42 [inline]
 __clear_bit_le include/asm-generic/bitops/le.h:105 [inline]
 mb_clear_bit fs/ext4/mballoc.c:473 [inline]
 mb_clear_bits fs/ext4/mballoc.c:1656 [inline]
 ext4_free_blocks+0x13b6/0x1b50 fs/ext4/mballoc.c:5987
 ext4_remove_blocks+0x529/0x800 fs/ext4/extents.c:2480
 ext4_ext_rm_leaf+0x670/0xd20 fs/ext4/extents.c:2664
 ext4_ext_remove_space+0x901/0x1300 fs/ext4/extents.c:2912
 ext4_ext_truncate+0xfe/0x170 fs/ext4/extents.c:4373
 ext4_truncate+0x76e/0xa80 fs/ext4/inode.c:4262
 ext4_setattr+0xacc/0xec0 fs/ext4/inode.c:5504
 notify_change+0x8a3/0xa80 fs/attr.c:398
 do_truncate fs/open.c:64 [inline]
 do_sys_ftruncate+0x405/0x4c0 fs/open.c:196
 __do_sys_ftruncate fs/open.c:207 [inline]
 __se_sys_ftruncate fs/open.c:205 [inline]
 __x64_sys_ftruncate+0x2f/0x40 fs/open.c:205
 do_syscall_64+0x4a/0x90 arch/x86/entry/common.c:47
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff888132adc000 of 1024 bytes by task 7483 on cpu 0:
 instrument_copy_to_user include/linux/instrumented.h:119 [inline]
 copyout lib/iov_iter.c:189 [inline]
 copy_page_to_iter_iovec lib/iov_iter.c:261 [inline]
 copy_page_to_iter+0x320/0x860 lib/iov_iter.c:973
 filemap_read+0xf06/0x1230 mm/filemap.c:2605
 generic_file_read_iter+0x75/0x2c0 mm/filemap.c:2701
 blkdev_read_iter+0xb9/0xf0 fs/block_dev.c:1730
 call_read_iter include/linux/fs.h:2108 [inline]
 new_sync_read fs/read_write.c:415 [inline]
 vfs_read+0x565/0x5d0 fs/read_write.c:496
 ksys_read+0xce/0x180 fs/read_write.c:634
 __do_sys_read fs/read_write.c:644 [inline]
 __se_sys_read fs/read_write.c:642 [inline]
 __x64_sys_read+0x3e/0x50 fs/read_write.c:642
 do_syscall_64+0x4a/0x90 arch/x86/entry/common.c:47
 entry_SYSCALL_64_after_hwframe+0x44/0xae

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 7483 Comm: systemd-udevd Not tainted 5.13.0-rc7-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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