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BUG: KCSAN: data-race in ext4_handle_inode_extension / mpage_process_page_bufs

write to 0xffff88800b6396b0 of 8 bytes by task 10139 on cpu 1:
 i_size_write include/linux/fs.h:872 [inline]
 ext4_update_inode_size fs/ext4/ext4.h:3289 [inline]
 ext4_handle_inode_extension+0x226/0x550 fs/ext4/file.c:331
 ext4_dio_write_iter fs/ext4/file.c:557 [inline]
 ext4_file_write_iter+0xef4/0x10b0 fs/ext4/file.c:661
 call_write_iter include/linux/fs.h:1977 [inline]
 do_iter_readv_writev+0x2cb/0x360 fs/read_write.c:740
 do_iter_write+0x112/0x4c0 fs/read_write.c:866
 vfs_iter_write+0x4c/0x70 fs/read_write.c:907
 iter_file_splice_write+0x40a/0x750 fs/splice.c:689
 do_splice_from fs/splice.c:767 [inline]
 direct_splice_actor+0x80/0xa0 fs/splice.c:936
 splice_direct_to_actor+0x345/0x650 fs/splice.c:891
 do_splice_direct+0xf5/0x170 fs/splice.c:979
 do_sendfile+0x7a6/0xe20 fs/read_write.c:1260
 __do_sys_sendfile64 fs/read_write.c:1325 [inline]
 __se_sys_sendfile64 fs/read_write.c:1311 [inline]
 __x64_sys_sendfile64+0xf2/0x130 fs/read_write.c:1311
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff88800b6396b0 of 8 bytes by task 10136 on cpu 0:
 i_size_read include/linux/fs.h:850 [inline]
 mpage_process_page_bufs+0x34/0x5f0 fs/ext4/inode.c:2194
 mpage_prepare_extent_to_map+0x4e6/0x640 fs/ext4/inode.c:2628
 ext4_writepages+0x674/0x1e70 fs/ext4/inode.c:2756
 do_writepages+0x7b/0x150 mm/page-writeback.c:2352
 __filemap_fdatawrite_range+0x19d/0x1d0 mm/filemap.c:424
 __filemap_fdatawrite mm/filemap.c:432 [inline]
 filemap_flush+0x1f/0x30 mm/filemap.c:459
 ext4_alloc_da_blocks+0x4a/0x100 fs/ext4/inode.c:3166
 ext4_release_file+0x5b/0x1d0 fs/ext4/file.c:141
 __fput+0x263/0x4f0 fs/file_table.c:280
 ____fput+0x11/0x20 fs/file_table.c:313
 task_work_run+0x8e/0x110 kernel/task_work.c:140
 tracehook_notify_resume include/linux/tracehook.h:189 [inline]
 exit_to_user_mode_loop kernel/entry/common.c:174 [inline]
 exit_to_user_mode_prepare+0x17c/0x1b0 kernel/entry/common.c:208
 __syscall_exit_to_user_mode_work kernel/entry/common.c:290 [inline]
 syscall_exit_to_user_mode+0x20/0x40 kernel/entry/common.c:301
 do_syscall_64+0x45/0x80 arch/x86/entry/common.c:56
 entry_SYSCALL_64_after_hwframe+0x44/0xae

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 10136 Comm: syz-executor.5 Not tainted 5.12.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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