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BUG: KCSAN: data-race in __send_signal / page_cache_ra_unbounded

write to 0xffff888100f7402c of 4 bytes by task 8418 on cpu 0:
 memalloc_nofs_restore include/linux/sched/mm.h:258 [inline]
 page_cache_ra_unbounded+0x484/0x4c0 mm/readahead.c:239
 do_page_cache_ra+0xa7/0xc0 mm/readahead.c:267
 do_sync_mmap_readahead+0x32a/0x360 mm/filemap.c:2733
 filemap_fault+0x1ba/0xbf0 mm/filemap.c:2821
 ext4_filemap_fault+0x4b/0x60 fs/ext4/inode.c:6205
 __do_fault mm/memory.c:3625 [inline]
 do_shared_fault+0xc3/0x7a0 mm/memory.c:4073
 do_fault mm/memory.c:4151 [inline]
 handle_pte_fault mm/memory.c:4387 [inline]
 __handle_mm_fault mm/memory.c:4522 [inline]
 handle_mm_fault+0x1285/0x17b0 mm/memory.c:4620
 do_user_addr_fault+0x433/0x830 arch/x86/mm/fault.c:1393
 handle_page_fault arch/x86/mm/fault.c:1450 [inline]
 exc_page_fault+0x94/0x2a0 arch/x86/mm/fault.c:1506
 asm_exc_page_fault+0x1e/0x30 arch/x86/include/asm/idtentry.h:580

read to 0xffff888100f7402c of 4 bytes by task 8419 on cpu 1:
 __send_signal+0x276/0x780 kernel/signal.c:1099
 send_signal+0x39f/0x3d0 kernel/signal.c:1242
 do_send_sig_info+0x9b/0xe0 kernel/signal.c:1291
 do_send_specific+0xc7/0x100 kernel/signal.c:3819
 do_tkill kernel/signal.c:3845 [inline]
 __do_sys_tgkill kernel/signal.c:3864 [inline]
 __se_sys_tgkill kernel/signal.c:3858 [inline]
 __x64_sys_tgkill+0x108/0x140 kernel/signal.c:3858
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 8419 Comm: syz-fuzzer Not tainted 5.11.0-rc5-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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