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BUG: KCSAN: data-race in kthread_is_per_cpu / page_cache_ra_unbounded

write to 0xffff88812f9660ac of 4 bytes by task 13897 on cpu 0:
 memalloc_nofs_save include/linux/sched/mm.h:249 [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:879 [inline]
 filemap_get_pages mm/filemap.c:2467 [inline]
 filemap_read+0x388/0x1230 mm/filemap.c:2550
 generic_file_read_iter+0x75/0x2c0 mm/filemap.c:2701
 blkdev_read_iter+0xb9/0xf0 fs/block_dev.c:1732
 call_read_iter include/linux/fs.h:2108 [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 0xffff88812f9660ac of 4 bytes by interrupt on cpu 1:
 __to_kthread kernel/kthread.c:101 [inline]
 kthread_is_per_cpu+0x2d/0x80 kernel/kthread.c:540
 can_migrate_task+0xf/0x180 kernel/sched/fair.c:7615
 detach_tasks+0xab/0x380 kernel/sched/fair.c:7779
 load_balance+0x768/0xcc0 kernel/sched/fair.c:9679
 rebalance_domains+0x1ae/0x2d0 kernel/sched/fair.c:10058
 __do_softirq+0x12c/0x275 kernel/softirq.c:559
 invoke_softirq kernel/softirq.c:433 [inline]
 __irq_exit_rcu+0xa5/0xb0 kernel/softirq.c:637
 sysvec_apic_timer_interrupt+0x69/0x80 arch/x86/kernel/apic/apic.c:1100
 asm_sysvec_apic_timer_interrupt+0x12/0x20 arch/x86/include/asm/idtentry.h:647
 smap_restore arch/x86/include/asm/smap.h:67 [inline]
 kcsan_setup_watchpoint+0x436/0x470 kernel/kcsan/core.c:595
 memcmp+0x33/0x60 lib/string.c:939
 memcmp_pages+0x89/0xe0
 pages_identical include/linux/mm.h:3196 [inline]
 uprobe_write_opcode+0x63f/0x1050 kernel/events/uprobes.c:533
 set_orig_insn+0x2c/0x40
 remove_breakpoint kernel/events/uprobes.c:926 [inline]
 register_for_each_vma+0x7ae/0x890 kernel/events/uprobes.c:1073
 uprobe_apply+0x8b/0x260 kernel/events/uprobes.c:1229
 uprobe_perf_close+0x2f8/0x370 kernel/trace/trace_uprobe.c:1292
 trace_uprobe_register+0x156/0x410 kernel/trace/trace_uprobe.c:1471
 perf_trace_event_close kernel/trace/trace_event_perf.c:192 [inline]
 perf_uprobe_destroy+0x58/0x90 kernel/trace/trace_event_perf.c:348
 _free_event+0x7db/0x9a0 kernel/events/core.c:4949
 put_event kernel/events/core.c:5043 [inline]
 perf_event_release_kernel+0x7bc/0x830 kernel/events/core.c:5158
 perf_release+0x21/0x30 kernel/events/core.c:5168
 __fput+0x25b/0x4e0 fs/file_table.c:280
 ____fput+0x11/0x20 fs/file_table.c:313
 task_work_run+0xae/0x130 kernel/task_work.c:164
 tracehook_notify_resume include/linux/tracehook.h:189 [inline]
 exit_to_user_mode_loop kernel/entry/common.c:174 [inline]
 exit_to_user_mode_prepare+0x156/0x190 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: 1 PID: 13880 Comm: syz-executor.2 Tainted: G        W         5.13.0-rc2-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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