syzbot

rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
rcu: 	Tasks blocked on level-0 rcu_node (CPUs 0-1): P4596/1:b..l
	(detected by 1, t=10502 jiffies, g=10321, q=42)
task:syz.0.87        state:R  running task     stack:24000 pid: 4596 ppid:  4184 flags:0x00004004
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5030 [inline]
 __schedule+0x11b8/0x43b0 kernel/sched/core.c:6376
 preempt_schedule_irq+0xb1/0x150 kernel/sched/core.c:6780
 irqentry_exit+0x63/0x70 kernel/entry/common.c:432
 asm_sysvec_apic_timer_interrupt+0x16/0x20 arch/x86/include/asm/idtentry.h:676
RIP: 0010:lock_acquire+0x1f2/0x3f0 kernel/locking/lockdep.c:5627
Code: 00 9c 8f 84 24 80 00 00 00 f6 84 24 81 00 00 00 02 0f 85 f6 00 00 00 41 f7 c6 00 02 00 00 74 01 fb 48 c7 44 24 60 0e 36 e0 45 <4b> c7 44 3d 00 00 00 00 00 66 43 c7 44 3d 09 00 00 43 c6 44 3d 0b
RSP: 0018:ffffc90003517180 EFLAGS: 00000206
RAX: 0000000000000001 RBX: 0000000000000000 RCX: fbe66b5df3dc0400
RDX: 0000000000000000 RSI: ffffffff8a0b2860 RDI: ffffffff8a599340
RBP: ffffc90003517288 R08: dffffc0000000000 R09: fffffbfff1ff6e19
R10: fffffbfff1ff6e19 R11: 1ffffffff1ff6e18 R12: ffffffff8c11c360
R13: 1ffff920006a2e3c R14: 0000000000000246 R15: dffffc0000000000
 rcu_lock_acquire+0x2a/0x30 include/linux/rcupdate.h:312
 rcu_read_lock include/linux/rcupdate.h:739 [inline]
 blk_cgroup_congested include/linux/blk-cgroup.h:280 [inline]
 __cgroup_throttle_swaprate+0x75/0x530 mm/swapfile.c:3809
 cgroup_throttle_swaprate include/linux/swap.h:728 [inline]
 shmem_add_to_page_cache+0xb7b/0x14b0 mm/shmem.c:727
 shmem_getpage_gfp+0x1793/0x2d40 mm/shmem.c:1940
 shmem_fault+0x1a9/0x520 mm/shmem.c:2118
 __do_fault+0x141/0x330 mm/memory.c:3928
 do_read_fault mm/memory.c:4264 [inline]
 do_fault mm/memory.c:4392 [inline]
 handle_pte_fault mm/memory.c:4650 [inline]
 __handle_mm_fault mm/memory.c:4785 [inline]
 handle_mm_fault+0x2949/0x43c0 mm/memory.c:4883
 do_user_addr_fault+0x489/0xc80 arch/x86/mm/fault.c:1357
 handle_page_fault arch/x86/mm/fault.c:1445 [inline]
 exc_page_fault+0x60/0x100 arch/x86/mm/fault.c:1501
 asm_exc_page_fault+0x22/0x30 arch/x86/include/asm/idtentry.h:606
RIP: 0010:copy_user_generic_unrolled+0x86/0xc0 arch/x86/lib/copy_user_64.S:91
Code: 4c 8b 5e 38 4c 89 47 20 4c 89 4f 28 4c 89 57 30 4c 89 5f 38 48 8d 76 40 48 8d 7f 40 ff c9 75 b6 89 d1 83 e2 07 c1 e9 03 74 12 <4c> 8b 06 4c 89 07 48 8d 76 08 48 8d 7f 08 ff c9 75 ee 21 d2 74 10
RSP: 0018:ffffc90003517a60 EFLAGS: 00050202
RAX: ffffffff83da7c01 RBX: 0000000000000038 RCX: 0000000000000007
RDX: 0000000000000000 RSI: 000020000029b000 RDI: ffffc90003517b00
RBP: 0000000000000000 R08: dffffc0000000000 R09: fffff520006a2f67
R10: fffff520006a2f67 R11: 1ffff920006a2f60 R12: 00007ffffffff000
R13: 000020000029b038 R14: ffffc90003517b00 R15: 000020000029b000
 copy_user_generic arch/x86/include/asm/uaccess_64.h:37 [inline]
 raw_copy_from_user arch/x86/include/asm/uaccess_64.h:52 [inline]
 _copy_from_user+0xfa/0x170 lib/usercopy.c:23
 copy_from_user include/linux/uaccess.h:192 [inline]
 __copy_msghdr_from_user net/socket.c:2318 [inline]
 copy_msghdr_from_user net/socket.c:2369 [inline]
 recvmsg_copy_msghdr net/socket.c:2621 [inline]
 ___sys_recvmsg+0x129/0x4f0 net/socket.c:2693
 do_recvmmsg+0x344/0x7a0 net/socket.c:2791
 __sys_recvmmsg net/socket.c:2870 [inline]
 __do_sys_recvmmsg net/socket.c:2893 [inline]
 __se_sys_recvmmsg net/socket.c:2886 [inline]
 __x64_sys_recvmmsg+0x18d/0x240 net/socket.c:2886
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x66/0xd0
RIP: 0033:0x7fc45a574be9
RSP: 002b:00007fc4587bb038 EFLAGS: 00000246 ORIG_RAX: 000000000000012b
RAX: ffffffffffffffda RBX: 00007fc45a79c090 RCX: 00007fc45a574be9
RDX: 0000000000010106 RSI: 00002000000000c0 RDI: 0000000000000006
RBP: 00007fc45a5f7e19 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000002 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fc45a79c128 R14: 00007fc45a79c090 R15: 00007fff3e0169f8
 </TASK>
rcu: rcu_preempt kthread starved for 10423 jiffies! g10321 f0x0 RCU_GP_WAIT_FQS(5) ->state=0x0 ->cpu=0
rcu: 	Unless rcu_preempt kthread gets sufficient CPU time, OOM is now expected behavior.
rcu: RCU grace-period kthread stack dump:
task:rcu_preempt     state:R  running task     stack:28032 pid:   15 ppid:     2 flags:0x00004000
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5030 [inline]
 __schedule+0x11b8/0x43b0 kernel/sched/core.c:6376
 schedule+0x11b/0x1e0 kernel/sched/core.c:6459
 schedule_timeout+0x15c/0x280 kernel/time/timer.c:1914
 rcu_gp_fqs_loop+0x29e/0x11b0 kernel/rcu/tree.c:1972
 rcu_gp_kthread+0x98/0x350 kernel/rcu/tree.c:2145
 kthread+0x436/0x520 kernel/kthread.c:334
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:287
 </TASK>
rcu: Stack dump where RCU GP kthread last ran:
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0 skipped: idling at native_safe_halt arch/x86/include/asm/irqflags.h:51 [inline]
NMI backtrace for cpu 0 skipped: idling at arch_safe_halt arch/x86/include/asm/irqflags.h:89 [inline]
NMI backtrace for cpu 0 skipped: idling at default_idle+0xb/0x10 arch/x86/kernel/process.c:728