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BUG: KCSAN: data-race in ext4_mark_iloc_dirty / generic_update_time

read to 0xffff888128d17b00 of 8 bytes by task 29 on cpu 1:
 ext4_do_update_inode fs/ext4/inode.c:4958 [inline]
 ext4_mark_iloc_dirty+0x426/0x1500 fs/ext4/inode.c:5578
 ext4_mark_inode_dirty+0xe6/0x420 fs/ext4/inode.c:5771
 mpage_map_and_submit_extent fs/ext4/inode.c:2479 [inline]
 ext4_writepages+0x12e4/0x1d40 fs/ext4/inode.c:2772
 do_writepages+0x6b/0x170 mm/page-writeback.c:2344
 __writeback_single_inode+0xaa/0x910 fs/fs-writeback.c:1452
 writeback_sb_inodes+0x4c8/0xa10 fs/fs-writeback.c:1716
 wb_writeback+0x1f9/0x6a0 fs/fs-writeback.c:1892
 wb_do_writeback fs/fs-writeback.c:2037 [inline]
 wb_workfn+0x215/0x970 fs/fs-writeback.c:2078
 process_one_work+0x424/0x930 kernel/workqueue.c:2264
 worker_thread+0x9a/0x7e0 kernel/workqueue.c:2410
 kthread+0x1cb/0x1f0 kernel/kthread.c:255
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:352

write to 0xffff888128d17b00 of 16 bytes by task 25966 on cpu 0:
 generic_update_time+0x109/0x270 fs/inode.c:1674
 update_time+0x7d/0x90 fs/inode.c:1694
 file_update_time+0x205/0x2d0 fs/inode.c:1909
 file_modified fs/inode.c:1932 [inline]
 file_modified+0x60/0x80 fs/inode.c:1917
 ext4_write_checks+0x4a/0x70 fs/ext4/file.c:249
 ext4_buffered_write_iter+0x87/0x280 fs/ext4/file.c:265
 ext4_file_write_iter+0xf4/0xd30 fs/ext4/file.c:642
 call_write_iter include/linux/fs.h:1901 [inline]
 do_iter_readv_writev+0x4a7/0x5d0 fs/read_write.c:693
 do_iter_write fs/read_write.c:998 [inline]
 do_iter_write+0x137/0x3a0 fs/read_write.c:979
 vfs_iter_write+0x56/0x80 fs/read_write.c:1039
 iter_file_splice_write+0x530/0x830 fs/splice.c:760
 ovl_splice_write+0xd7/0x140 fs/overlayfs/file.c:402
 do_splice_from fs/splice.c:863 [inline]
 direct_splice_actor+0x97/0xb0 fs/splice.c:1037
 splice_direct_to_actor+0x22f/0x540 fs/splice.c:992
 do_splice_direct+0x152/0x1d0 fs/splice.c:1080
 do_sendfile+0x396/0x810 fs/read_write.c:1520
 __do_sys_sendfile64 fs/read_write.c:1581 [inline]
 __se_sys_sendfile64 fs/read_write.c:1567 [inline]
 __x64_sys_sendfile64+0x121/0x140 fs/read_write.c:1567
 do_syscall_64+0xc7/0x390 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 25966 Comm: syz-executor.0 Not tainted 5.6.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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