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BUG: KCSAN: data-race in prandom_seed / prandom_u32

write to 0xffff88813bd28500 of 8 bytes by interrupt on cpu 1:
 siprand_u32 lib/random32.c:372 [inline]
 prandom_u32+0xeb/0x1f0 lib/random32.c:387
 mld_ifc_start_timer net/ipv6/mcast.c:1048 [inline]
 mld_ifc_timer_expire+0x6e5/0x800 net/ipv6/mcast.c:2478
 call_timer_fn+0x2e/0x240 kernel/time/timer.c:1431
 expire_timers+0x116/0x260 kernel/time/timer.c:1476
 __run_timers+0x358/0x3f0 kernel/time/timer.c:1745
 run_timer_softirq+0x19/0x30 kernel/time/timer.c:1758
 __do_softirq+0x13c/0x2c3 kernel/softirq.c:345
 invoke_softirq kernel/softirq.c:221 [inline]
 __irq_exit_rcu+0xb4/0xc0 kernel/softirq.c:422
 sysvec_apic_timer_interrupt+0x6e/0x80 arch/x86/kernel/apic/apic.c:1100
 asm_sysvec_apic_timer_interrupt+0x12/0x20 arch/x86/include/asm/idtentry.h:632
 is_atomic kernel/kcsan/core.c:248 [inline]
 should_watch kernel/kcsan/core.c:261 [inline]
 check_access kernel/kcsan/core.c:627 [inline]
 __tsan_read8+0x13a/0x180 kernel/kcsan/core.c:840
 xas_error include/linux/xarray.h:1389 [inline]
 xas_find+0x26/0x3d0 lib/xarray.c:1235
 xas_next_entry include/linux/xarray.h:1640 [inline]
 next_map_page mm/filemap.c:3086 [inline]
 filemap_map_pages+0x612/0x770 mm/filemap.c:3142
 do_fault_around mm/memory.c:3920 [inline]
 do_read_fault+0x217/0x530 mm/memory.c:3934
 do_fault mm/memory.c:4067 [inline]
 handle_pte_fault mm/memory.c:4318 [inline]
 __handle_mm_fault mm/memory.c:4453 [inline]
 handle_mm_fault+0x1019/0x1840 mm/memory.c:4551
 faultin_page mm/gup.c:850 [inline]
 __get_user_pages+0xa47/0x1000 mm/gup.c:1069
 populate_vma_page_range mm/gup.c:1402 [inline]
 __mm_populate+0x24d/0x380 mm/gup.c:1450
 mm_populate include/linux/mm.h:2582 [inline]
 vm_mmap_pgoff+0x14c/0x1d0 mm/util.c:524
 ksys_mmap_pgoff+0xe1/0x380 mm/mmap.c:1632
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff88813bd28500 of 8 bytes by task 3801 on cpu 0:
 prandom_seed+0xc5/0x270 lib/random32.c:440
 addrconf_dad_begin net/ipv6/addrconf.c:3939 [inline]
 addrconf_dad_work+0x258/0x1160 net/ipv6/addrconf.c:4064
 process_one_work+0x3e1/0x950 kernel/workqueue.c:2275
 worker_thread+0x616/0xa70 kernel/workqueue.c:2421
 kthread+0x20b/0x230 kernel/kthread.c:292
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 3801 Comm: kworker/0:3 Not tainted 5.12.0-rc4-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: ipv6_addrconf addrconf_dad_work
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