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BUG: KCSAN: data-race in do_epoll_wait / ep_poll_callback

write to 0xffff8881245a6350 of 8 bytes by interrupt on cpu 0:
 list_add_tail_lockless fs/eventpoll.c:1158 [inline]
 ep_poll_callback+0x29c/0x510 fs/eventpoll.c:1248
 __wake_up_common+0xbc/0x130 kernel/sched/wait.c:93
 __wake_up_common_lock kernel/sched/wait.c:123 [inline]
 __wake_up_sync_key+0x83/0xc0 kernel/sched/wait.c:190
 sock_def_readable+0x61/0xd0 net/core/sock.c:2909
 tcp_data_ready net/ipv4/tcp_input.c:4794 [inline]
 tcp_rcv_established+0xfb4/0x1110 net/ipv4/tcp_input.c:5722
 tcp_v4_do_rcv+0x25e/0x480 net/ipv4/tcp_ipv4.c:1629
 tcp_v4_rcv+0x2159/0x23e0 net/ipv4/tcp_ipv4.c:2011
 ip_protocol_deliver_rcu+0x1f9/0x400 net/ipv4/ip_input.c:204
 ip_local_deliver_finish net/ipv4/ip_input.c:231 [inline]
 NF_HOOK include/linux/netfilter.h:307 [inline]
 ip_local_deliver+0x1d6/0x2a0 net/ipv4/ip_input.c:252
 dst_input include/net/dst.h:441 [inline]
 ip_sublist_rcv_finish net/ipv4/ip_input.c:550 [inline]
 ip_list_rcv_finish net/ipv4/ip_input.c:600 [inline]
 ip_sublist_rcv+0x4d4/0x5a0 net/ipv4/ip_input.c:608
 ip_list_rcv+0x262/0x290 net/ipv4/ip_input.c:643
 __netif_receive_skb_list_ptype net/core/dev.c:5324 [inline]
 __netif_receive_skb_list_core+0x34b/0x450 net/core/dev.c:5372
 __netif_receive_skb_list+0x298/0x310 net/core/dev.c:5424
 netif_receive_skb_list_internal+0xda/0x330 net/core/dev.c:5531
 gro_normal_list net/core/dev.c:5642 [inline]
 gro_normal_one net/core/dev.c:5654 [inline]
 napi_skb_finish net/core/dev.c:5982 [inline]
 napi_gro_receive+0x329/0x5a0 net/core/dev.c:6014
 receive_buf+0x7a4/0xcf0 drivers/net/virtio_net.c:1082
 virtnet_receive drivers/net/virtio_net.c:1346 [inline]
 virtnet_poll+0x2fa/0x780 drivers/net/virtio_net.c:1451
 napi_poll+0x154/0x480 net/core/dev.c:6684
 net_rx_action+0x1ba/0x530 net/core/dev.c:6752
 __do_softirq+0x198/0x360 kernel/softirq.c:292
 asm_call_on_stack+0xf/0x20 arch/x86/entry/entry_64.S:711
 __run_on_irqstack arch/x86/include/asm/irq_stack.h:22 [inline]
 run_on_irqstack_cond arch/x86/include/asm/irq_stack.h:48 [inline]
 do_softirq_own_stack+0x5d/0x80 arch/x86/kernel/irq_64.c:77
 invoke_softirq kernel/softirq.c:387 [inline]
 __irq_exit_rcu+0x115/0x120 kernel/softirq.c:417
 common_interrupt+0x14e/0x1e0 arch/x86/kernel/irq.c:239
 asm_common_interrupt+0x1e/0x40 arch/x86/include/asm/idtentry.h:587
 arch_local_irq_restore arch/x86/include/asm/paravirt.h:765 [inline]
 kcsan_setup_watchpoint+0x47c/0x4d0 kernel/kcsan/core.c:542
 arch_local_irq_disable arch/x86/include/asm/paravirt.h:770 [inline]
 arch_local_irq_save arch/x86/include/asm/paravirt.h:783 [inline]
 __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:108 [inline]
 _raw_spin_lock_irqsave+0x33/0x90 kernel/locking/spinlock.c:159
 __test_set_page_writeback+0x1e2/0x420 mm/page-writeback.c:2786
 ext4_bio_write_page+0xc7/0xcd0 fs/ext4/page-io.c:451
 mpage_submit_page+0xf4/0x170 fs/ext4/inode.c:2082
 mpage_map_and_submit_buffers fs/ext4/inode.c:2330 [inline]
 mpage_map_and_submit_extent fs/ext4/inode.c:2469 [inline]
 ext4_writepages+0x106b/0x1cb0 fs/ext4/inode.c:2782
 do_writepages+0x7b/0x150 mm/page-writeback.c:2354
 __filemap_fdatawrite_range+0x19b/0x1d0 mm/filemap.c:421
 __filemap_fdatawrite mm/filemap.c:429 [inline]
 filemap_flush+0x1f/0x30 mm/filemap.c:456
 collapse_file+0x1f65/0x2110 mm/khugepaged.c:1737
 khugepaged_scan_file mm/khugepaged.c:2011 [inline]
 khugepaged_scan_mm_slot mm/khugepaged.c:2107 [inline]
 khugepaged_do_scan+0x1018/0x1380 mm/khugepaged.c:2193
 khugepaged+0x75/0x670 mm/khugepaged.c:2238
 kthread+0x210/0x220 kernel/kthread.c:291
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:293

read to 0xffff8881245a6350 of 8 bytes by task 8629 on cpu 1:
 list_empty_careful include/linux/list.h:300 [inline]
 ep_events_available fs/eventpoll.c:379 [inline]
 ep_poll fs/eventpoll.c:1855 [inline]
 do_epoll_wait+0x2e2/0x840 fs/eventpoll.c:2333
 __do_sys_epoll_pwait fs/eventpoll.c:2364 [inline]
 __se_sys_epoll_pwait fs/eventpoll.c:2350 [inline]
 __x64_sys_epoll_pwait+0x92/0x140 fs/eventpoll.c:2350
 do_syscall_64+0x71/0x120 arch/x86/entry/common.c:359
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 8629 Comm: syz-fuzzer Not tainted 5.8.0-rc2-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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