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BUG: KCSAN: data-race in mm_update_next_owner / page_cache_ra_unbounded

write to 0xffff88812d8b50ac of 4 bytes by task 1905 on cpu 1:
 memalloc_nofs_save include/linux/sched/mm.h:245 [inline]
 page_cache_ra_unbounded+0xa8/0x410 mm/readahead.c:193
 do_page_cache_ra mm/readahead.c:267 [inline]
 force_page_cache_ra+0x246/0x280 mm/readahead.c:299
 page_cache_sync_ra+0xcc/0xe0 mm/readahead.c:573
 page_cache_sync_readahead include/linux/pagemap.h:864 [inline]
 filemap_get_pages mm/filemap.c:2442 [inline]
 filemap_read+0x388/0x1230 mm/filemap.c:2525
 generic_file_read_iter+0x84/0x3e0 mm/filemap.c:2676
 blkdev_read_iter+0xb3/0xc0 fs/block_dev.c:1727
 call_read_iter include/linux/fs.h:2110 [inline]
 new_sync_read fs/read_write.c:415 [inline]
 vfs_read+0x565/0x5d0 fs/read_write.c:496
 ksys_read+0xce/0x180 fs/read_write.c:634
 __do_sys_read fs/read_write.c:644 [inline]
 __se_sys_read fs/read_write.c:642 [inline]
 __x64_sys_read+0x3e/0x50 fs/read_write.c:642
 do_syscall_64+0x4a/0x90 arch/x86/entry/common.c:47
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff88812d8b50ac of 4 bytes by task 1992 on cpu 0:
 mm_update_next_owner+0x1d9/0x520 kernel/exit.c:388
 exit_mm+0x358/0x450 kernel/exit.c:500
 do_exit+0x3ff/0x1560 kernel/exit.c:812
 do_group_exit+0xce/0x1a0 kernel/exit.c:922
 get_signal+0xf83/0x15d0 kernel/signal.c:2781
 arch_do_signal_or_restart+0x2a/0x220 arch/x86/kernel/signal.c:789
 handle_signal_work kernel/entry/common.c:147 [inline]
 exit_to_user_mode_loop kernel/entry/common.c:171 [inline]
 exit_to_user_mode_prepare+0x109/0x190 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+0x56/0x90 arch/x86/entry/common.c:57
 entry_SYSCALL_64_after_hwframe+0x44/0xae

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 1992 Comm: syz-executor.5 Not tainted 5.12.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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