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BUG: KCSAN: data-race in ext4_ext_try_to_merge_right / ext4_mark_iloc_dirty

write to 0xffff8880bb41d9a0 of 2 bytes by task 302 on cpu 0:
 ext4_ext_try_to_merge_right+0x285/0x4c0 fs/ext4/extents.c:1767
 ext4_ext_try_to_merge+0x6b/0x310 fs/ext4/extents.c:1851
 ext4_convert_unwritten_extents_endio fs/ext4/extents.c:3720 [inline]
 ext4_ext_handle_unwritten_extents+0x625/0xaa0 fs/ext4/extents.c:3848
 ext4_ext_map_blocks+0x758/0x20c0 fs/ext4/extents.c:4118
 ext4_map_blocks+0x6bf/0xf40 fs/ext4/inode.c:625
 ext4_convert_unwritten_extents+0x16a/0x2d0 fs/ext4/extents.c:4749
 ext4_convert_unwritten_io_end_vec+0xa4/0x130 fs/ext4/extents.c:4788
 ext4_end_io_end fs/ext4/page-io.c:187 [inline]
 ext4_do_flush_completed_IO fs/ext4/page-io.c:260 [inline]
 ext4_end_io_rsv_work+0x198/0x360 fs/ext4/page-io.c:274
 process_one_work+0x3e1/0x9a0 kernel/workqueue.c:2269
 worker_thread+0x665/0xbe0 kernel/workqueue.c:2415
 kthread+0x20d/0x230 kernel/kthread.c:292
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294

read to 0xffff8880bb41d9a0 of 4 bytes by task 15294 on cpu 1:
 ext4_do_update_inode fs/ext4/inode.c:5042 [inline]
 ext4_mark_iloc_dirty+0xd09/0x1660 fs/ext4/inode.c:5624
 __ext4_mark_inode_dirty+0x448/0x630 fs/ext4/inode.c:5818
 ext4_dirty_inode+0xa6/0xc0 fs/ext4/inode.c:5854
 __mark_inode_dirty+0x72/0x7f0 fs/fs-writeback.c:2260
 mark_inode_dirty include/linux/fs.h:2169 [inline]
 generic_write_end+0x166/0x250 fs/buffer.c:2202
 ext4_da_write_end+0x57e/0x760 fs/ext4/inode.c:3091
 generic_perform_write+0x23b/0x390 mm/filemap.c:3512
 ext4_buffered_write_iter+0x2cc/0x3b0 fs/ext4/file.c:269
 ext4_file_write_iter+0x768/0x1060 include/linux/fs.h:784
 call_write_iter include/linux/fs.h:1882 [inline]
 do_iter_readv_writev+0x32e/0x3d0 fs/read_write.c:713
 do_iter_write+0x112/0x4b0 fs/read_write.c:1018
 vfs_iter_write+0x4c/0x70 fs/read_write.c:1059
 iter_file_splice_write+0x41a/0x770 fs/splice.c:750
 do_splice_from fs/splice.c:846 [inline]
 direct_splice_actor+0x95/0x160 fs/splice.c:1016
 splice_direct_to_actor+0x365/0x660 fs/splice.c:971
 do_splice_direct+0xf2/0x170 fs/splice.c:1059
 do_sendfile+0x56a/0xba0 fs/read_write.c:1540
 __do_sys_sendfile64 fs/read_write.c:1601 [inline]
 __se_sys_sendfile64 fs/read_write.c:1587 [inline]
 __x64_sys_sendfile64+0xf2/0x130 fs/read_write.c:1587
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 15294 Comm: syz-executor.1 Not tainted 5.9.0-rc6-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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