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BUG: KCSAN: data-race in inet_putpeer / inet_putpeer

write to 0xffff8880b88108d0 of 4 bytes by interrupt on cpu 1:
 inet_putpeer+0x37/0xa0 net/ipv4/inetpeer.c:240
 ip4_frag_free+0x3d/0x50 net/ipv4/ip_fragment.c:102
 inet_frag_destroy_rcu+0x58/0x80 net/ipv4/inet_fragment.c:228
 __rcu_reclaim kernel/rcu/rcu.h:222 [inline]
 rcu_do_batch+0x256/0x5b0 kernel/rcu/tree.c:2157
 rcu_core+0x369/0x4d0 kernel/rcu/tree.c:2377
 rcu_core_si+0x12/0x20 kernel/rcu/tree.c:2386
 __do_softirq+0x115/0x33f kernel/softirq.c:292
 invoke_softirq kernel/softirq.c:373 [inline]
 irq_exit+0xbb/0xe0 kernel/softirq.c:413
 exiting_irq arch/x86/include/asm/apic.h:536 [inline]
 smp_apic_timer_interrupt+0xe6/0x280 arch/x86/kernel/apic/apic.c:1137
 apic_timer_interrupt+0xf/0x20 arch/x86/entry/entry_64.S:830
 find_watchpoint kernel/kcsan/core.c:67 [inline]
 check_access kernel/kcsan/core.c:388 [inline]
 __tsan_unaligned_write8+0x64/0x1f0 kernel/kcsan/core.c:530
 vma_gap_callbacks_rotate+0x3f/0x190 mm/mmap.c:439
 __rb_insert lib/rbtree.c:161 [inline]
 __rb_insert_augmented+0x2a9/0x370 lib/rbtree.c:459
 rb_insert_augmented include/linux/rbtree_augmented.h:50 [inline]
 vma_rb_insert mm/mmap.c:463 [inline]
 __vma_link_rb+0x3ef/0x440 mm/mmap.c:617
 __vma_link mm/mmap.c:645 [inline]
 __insert_vm_struct mm/mmap.c:681 [inline]
 __vma_adjust+0xbf4/0x12a0 mm/mmap.c:912
 vma_adjust include/linux/mm.h:2276 [inline]
 __split_vma+0x338/0x350 mm/mmap.c:2704
 __do_munmap+0xb02/0xb60 mm/mmap.c:2803
 __vm_munmap+0xb2/0x130 mm/mmap.c:2868
 __do_sys_munmap mm/mmap.c:2894 [inline]
 __se_sys_munmap mm/mmap.c:2890 [inline]
 __x64_sys_munmap+0x4c/0x60 mm/mmap.c:2890
 do_syscall_64+0xcc/0x370 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

write to 0xffff8880b88108d0 of 4 bytes by interrupt on cpu 0:
 inet_putpeer+0x37/0xa0 net/ipv4/inetpeer.c:240
 ip4_frag_free+0x3d/0x50 net/ipv4/ip_fragment.c:102
 inet_frag_destroy_rcu+0x58/0x80 net/ipv4/inet_fragment.c:228
 __rcu_reclaim kernel/rcu/rcu.h:222 [inline]
 rcu_do_batch+0x256/0x5b0 kernel/rcu/tree.c:2157
 rcu_core+0x369/0x4d0 kernel/rcu/tree.c:2377
 rcu_core_si+0x12/0x20 kernel/rcu/tree.c:2386
 __do_softirq+0x115/0x33f kernel/softirq.c:292
 invoke_softirq kernel/softirq.c:373 [inline]
 irq_exit+0xbb/0xe0 kernel/softirq.c:413
 exiting_irq arch/x86/include/asm/apic.h:536 [inline]
 smp_apic_timer_interrupt+0xe6/0x280 arch/x86/kernel/apic/apic.c:1137
 apic_timer_interrupt+0xf/0x20 arch/x86/entry/entry_64.S:830
 find_watchpoint kernel/kcsan/core.c:67 [inline]
 check_access kernel/kcsan/core.c:388 [inline]
 __tsan_read8+0x16/0x1f0 kernel/kcsan/core.c:530
 compound_head include/linux/page-flags.h:174 [inline]
 PageUptodate include/linux/page-flags.h:495 [inline]
 filemap_map_pages+0x2f4/0x990 mm/filemap.c:2654
 do_fault_around mm/memory.c:3450 [inline]
 do_read_fault mm/memory.c:3484 [inline]
 do_fault mm/memory.c:3618 [inline]
 handle_pte_fault mm/memory.c:3849 [inline]
 __handle_mm_fault+0x2544/0x2c70 mm/memory.c:3973
 handle_mm_fault+0x21b/0x530 mm/memory.c:4010
 do_user_addr_fault arch/x86/mm/fault.c:1441 [inline]
 __do_page_fault+0x3fb/0x9e0 arch/x86/mm/fault.c:1506
 do_page_fault+0x54/0x233 arch/x86/mm/fault.c:1530
 page_fault+0x34/0x40 arch/x86/entry/entry_64.S:1202

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 11723 Comm: syz-executor.0 Not tainted 5.4.0-rc6+ #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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