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BUG: KCSAN: data-race in mm_update_next_owner / page_cache_readahead_unbounded

write to 0xffff888085bb7064 of 4 bytes by task 22002 on cpu 1:
 memalloc_nofs_restore include/linux/sched/mm.h:273 [inline]
 page_cache_readahead_unbounded+0x409/0x440 mm/readahead.c:245
 __do_page_cache_readahead mm/readahead.c:273 [inline]
 force_page_cache_readahead+0x1ec/0x220 mm/readahead.c:303
 page_cache_sync_readahead+0x191/0x1a0 mm/readahead.c:580
 generic_file_buffered_read+0x2ae/0x1800 mm/filemap.c:2033
 generic_file_read_iter+0x7d/0x3e0 mm/filemap.c:2307
 blkdev_read_iter+0xb3/0xc0 fs/block_dev.c:2044
 call_read_iter include/linux/fs.h:1901 [inline]
 new_sync_read fs/read_write.c:415 [inline]
 __vfs_read+0x2d5/0x330 fs/read_write.c:428
 vfs_read+0x131/0x2a0 fs/read_write.c:462
 ksys_read+0xce/0x180 fs/read_write.c:588
 __do_sys_read fs/read_write.c:598 [inline]
 __se_sys_read fs/read_write.c:596 [inline]
 __x64_sys_read+0x3e/0x50 fs/read_write.c:596
 do_syscall_64+0x51/0xb0 arch/x86/entry/common.c:384
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff888085bb7064 of 4 bytes by task 22005 on cpu 0:
 mm_update_next_owner+0x1d9/0x4a0 kernel/exit.c:386
 exit_mm+0x2c0/0x330 kernel/exit.c:481
 do_exit+0x415/0x16e0 kernel/exit.c:792
 do_group_exit+0x17a/0x180 kernel/exit.c:903
 __do_sys_exit_group+0xb/0x10 kernel/exit.c:914
 __se_sys_exit_group+0x5/0x10 kernel/exit.c:912
 __x64_sys_exit_group+0x16/0x20 kernel/exit.c:912
 do_syscall_64+0x51/0xb0 arch/x86/entry/common.c:384
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 22005 Comm: syz-executor.1 Not tainted 5.8.0-rc4-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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