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BUG: KCSAN: data-race in mm_update_next_owner / page_cache_readahead_unbounded

write to 0xffff88807ab49064 of 4 bytes by task 2012 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+0x2c5/0x19e0 mm/filemap.c:2033
 generic_file_read_iter+0x7d/0x3e0 mm/filemap.c:2326
 blkdev_read_iter+0xb3/0xc0 fs/block_dev.c:2044
 call_read_iter include/linux/fs.h:1902 [inline]
 new_sync_read fs/read_write.c:415 [inline]
 vfs_read+0x523/0x590 fs/read_write.c:481
 ksys_read+0xce/0x180 fs/read_write.c:607
 __do_sys_read fs/read_write.c:617 [inline]
 __se_sys_read fs/read_write.c:615 [inline]
 __x64_sys_read+0x3e/0x50 fs/read_write.c:615
 do_syscall_64+0x51/0xb0 arch/x86/entry/common.c:384
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff88807ab49064 of 4 bytes by task 12579 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+0xcb/0x180 kernel/exit.c:903
 get_signal+0x106d/0x1650 kernel/signal.c:2743
 do_signal+0x25/0x270 arch/x86/kernel/signal.c:810
 exit_to_usermode_loop arch/x86/entry/common.c:235 [inline]
 __prepare_exit_to_usermode+0x127/0x230 arch/x86/entry/common.c:269
 __syscall_return_slowpath+0x47/0x60 arch/x86/entry/common.c:352
 do_syscall_64+0x5d/0xb0 arch/x86/entry/common.c:393
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 12579 Comm: syz-executor.2 Not tainted 5.8.0-rc7-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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