syzbot

==================================================================
BUG: KMSAN: uninit-value in rcu_segcblist_enqueue+0x239/0x2d0 kernel/rcu/rcu_segcblist.c:150
CPU: 1 PID: 4506 Comm: syz-executor653 Not tainted 4.17.0-rc5+ #101
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x185/0x1d0 lib/dump_stack.c:113
 kmsan_report+0x149/0x260 mm/kmsan/kmsan.c:1084
 __msan_warning_32+0x6e/0xc0 mm/kmsan/kmsan_instr.c:686
 rcu_segcblist_enqueue+0x239/0x2d0 kernel/rcu/rcu_segcblist.c:150
 __call_rcu+0x227/0xef0 kernel/rcu/tree.c:3057
 call_rcu_sched+0x32/0x40 kernel/rcu/tree.c:3097
 free_pid+0x441/0x450 kernel/pid.c:156
 __change_pid kernel/pid.c:294 [inline]
 detach_pid+0x35a/0x370 kernel/pid.c:299
 __unhash_process kernel/exit.c:75 [inline]
 __exit_signal kernel/exit.c:156 [inline]
 release_task+0x10a0/0x2530 kernel/exit.c:200
 wait_task_zombie kernel/exit.c:1163 [inline]
 wait_consider_task+0x2e29/0x4520 kernel/exit.c:1390
 do_wait_thread kernel/exit.c:1453 [inline]
 do_wait+0x5f8/0xbc0 kernel/exit.c:1524
 kernel_wait4+0x337/0x4b0 kernel/exit.c:1667
 __do_sys_wait4 kernel/exit.c:1679 [inline]
 __se_sys_wait4 kernel/exit.c:1675 [inline]
 __x64_sys_wait4+0x17c/0x320 kernel/exit.c:1675
 do_syscall_64+0x154/0x220 arch/x86/entry/common.c:287
 entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x40708a
RSP: 002b:00000000007ff868 EFLAGS: 00000246 ORIG_RAX: 000000000000003d
RAX: ffffffffffffffda RBX: 00000000000077dc RCX: 000000000040708a
RDX: 0000000040000001 RSI: 00000000007ff870 RDI: ffffffffffffffff
RBP: 00000000000077dc R08: 0000000000000001 R09: 0000000000d65880
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000000051e6
R13: 0000000000117995 R14: 0000000000000000 R15: 0000000000000000

Uninit was stored to memory at:
 kmsan_save_stack_with_flags mm/kmsan/kmsan.c:279 [inline]
 kmsan_save_stack mm/kmsan/kmsan.c:294 [inline]
 kmsan_internal_chain_origin+0x12b/0x210 mm/kmsan/kmsan.c:685
 __msan_chain_origin+0x69/0xc0 mm/kmsan/kmsan_instr.c:529
 rcu_segcblist_enqueue+0x275/0x2d0 kernel/rcu/rcu_segcblist.c:151
 __call_rcu+0x227/0xef0 kernel/rcu/tree.c:3057
 call_rcu_sched+0x32/0x40 kernel/rcu/tree.c:3097
 release_task+0x24b9/0x2530 kernel/exit.c:223
 exit_notify kernel/exit.c:736 [inline]
 do_exit+0x2d91/0x38d0 kernel/exit.c:887
 do_group_exit+0x1a0/0x360 kernel/exit.c:970
 get_signal+0x1320/0x1f20 kernel/signal.c:2482
 do_signal+0xb8/0x1c80 arch/x86/kernel/signal.c:810
 exit_to_usermode_loop arch/x86/entry/common.c:162 [inline]
 prepare_exit_to_usermode+0x271/0x3a0 arch/x86/entry/common.c:196
 syscall_return_slowpath+0xe9/0x700 arch/x86/entry/common.c:265
 do_syscall_64+0x1a6/0x220 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x44/0xa9
Uninit was created at:
 kmsan_save_stack_with_flags mm/kmsan/kmsan.c:279 [inline]
 kmsan_internal_poison_shadow+0xb8/0x1b0 mm/kmsan/kmsan.c:189
 kmsan_kmalloc+0x94/0x100 mm/kmsan/kmsan.c:315
 kmem_cache_alloc+0xad3/0xb90 mm/slub.c:2772
 alloc_pid+0x7f/0xce0 kernel/pid.c:168
 copy_process+0x3fb7/0x9bb0 kernel/fork.c:1809
 _do_fork+0x311/0xf00 kernel/fork.c:2089
 __do_sys_clone kernel/fork.c:2196 [inline]
 __se_sys_clone kernel/fork.c:2190 [inline]
 __x64_sys_clone+0x15e/0x1b0 kernel/fork.c:2190
 do_syscall_64+0x154/0x220 arch/x86/entry/common.c:287
 entry_SYSCALL_64_after_hwframe+0x44/0xa9
==================================================================