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Date:   Mon, 06 Jul 2020 08:42:24 -0700
From:   syzbot <>
Subject: INFO: rcu detected stall in __sys_sendmsg


syzbot found the following crash on:

HEAD commit:    7cc2a8ea Merge tag 'block-5.8-2020-07-01' of git://git.ker..
git tree:       upstream
console output:
kernel config:
dashboard link:
compiler:       clang version 10.0.0 ( c2443155a0fb245c8f17f2c1c72b6ea391e86e81)
syz repro:
C reproducer:

IMPORTANT: if you fix the bug, please add the following tag to the commit:

rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
rcu: 	0-...0: (1 GPs behind) idle=59a/1/0x4000000000000000 softirq=8266/8267 fqs=5250 
	(detected by 1, t=10502 jiffies, g=6117, q=61)
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0
CPU: 0 PID: 6826 Comm: syz-executor019 Not tainted 5.8.0-rc3-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
RIP: 0010:preempt_count_add+0xe/0x150 kernel/sched/core.c:3873
Code: 07 80 c1 03 38 c1 0f 8c 40 ff ff ff 48 89 ef e8 48 f2 62 00 e9 33 ff ff ff 0f 1f 00 41 57 41 56 53 89 fb 65 01 3d 4e 75 b1 7e <48> c7 c0 30 7d 5a 8b 48 c1 e8 03 49 bf 00 00 00 00 00 fc ff df 42
RSP: 0018:ffffc90000007cf0 EFLAGS: 00000006
RAX: 1ffff11012ddc459 RBX: 0000000000000001 RCX: ffff8880a8c44300
RDX: 0000000000010202 RSI: 0000000000000000 RDI: 0000000000000001
RBP: ffff888096ee2000 R08: ffffffff8164ef7e R09: fffffbfff12da576
R10: fffffbfff12da576 R11: 0000000000000000 R12: ffff888096ee2340
R13: dffffc0000000000 R14: ffff888096ee22e8 R15: ffff888096ee2340
FS:  0000000000753880(0000) GS:ffff8880ae800000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000020000610 CR3: 00000000a9a34000 CR4: 00000000001406f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 __raw_spin_lock include/linux/spinlock_api_smp.h:141 [inline]
 _raw_spin_lock+0xe/0x40 kernel/locking/spinlock.c:151
 spin_lock include/linux/spinlock.h:353 [inline]
 advance_sched+0x47/0x8c0 net/sched/sch_taprio.c:699
 __run_hrtimer kernel/time/hrtimer.c:1520 [inline]
 __hrtimer_run_queues+0x47f/0x930 kernel/time/hrtimer.c:1584
 hrtimer_interrupt+0x373/0xd60 kernel/time/hrtimer.c:1646
 local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1080 [inline]
 __sysvec_apic_timer_interrupt+0xf0/0x260 arch/x86/kernel/apic/apic.c:1097
 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]
 sysvec_apic_timer_interrupt+0xb9/0x130 arch/x86/kernel/apic/apic.c:1091
 asm_sysvec_apic_timer_interrupt+0x12/0x20 arch/x86/include/asm/idtentry.h:596
RIP: 0010:arch_local_irq_restore arch/x86/include/asm/paravirt.h:765 [inline]
RIP: 0010:__raw_spin_unlock_irqrestore include/linux/spinlock_api_smp.h:160 [inline]
RIP: 0010:_raw_spin_unlock_irqrestore+0xa5/0xd0 kernel/locking/spinlock.c:191
Code: b9 00 00 00 00 00 fc ff df 80 3c 08 00 74 0c 48 c7 c7 f0 c7 2b 89 e8 ea 7c 94 f9 48 83 3d d2 c9 0c 01 00 74 2c 4c 89 f7 57 9d <0f> 1f 44 00 00 bf 01 00 00 00 e8 cc 8b 31 f9 65 8b 05 d1 ff e2 77
RSP: 0018:ffffc90001277408 EFLAGS: 00000282
RAX: 1ffffffff12578fe RBX: ffff888096ee22e8 RCX: dffffc0000000000
RDX: 0000000000000000 RSI: 0000000000000008 RDI: 0000000000000282
RBP: ffffc90001277600 R08: dffffc0000000000 R09: fffffbfff16334b8
R10: fffffbfff16334b8 R11: 0000000000000000 R12: ffff888096ee2340
R13: 0000000000000000 R14: 0000000000000282 R15: 161f1f2ad520785b
 spin_unlock_irqrestore include/linux/spinlock.h:408 [inline]
 taprio_change+0x4245/0x51f0 net/sched/sch_taprio.c:1557
 qdisc_create+0x7d1/0x1410 net/sched/sch_api.c:1246
 tc_modify_qdisc+0x962/0x1d90 net/sched/sch_api.c:1662
 rtnetlink_rcv_msg+0x889/0xd40 net/core/rtnetlink.c:5460
 netlink_rcv_skb+0x190/0x3a0 net/netlink/af_netlink.c:2469
 netlink_unicast_kernel net/netlink/af_netlink.c:1303 [inline]
 netlink_unicast+0x786/0x940 net/netlink/af_netlink.c:1329
 netlink_sendmsg+0xa57/0xd70 net/netlink/af_netlink.c:1918
 sock_sendmsg_nosec net/socket.c:652 [inline]
 sock_sendmsg net/socket.c:672 [inline]
 ____sys_sendmsg+0x519/0x800 net/socket.c:2352
 ___sys_sendmsg net/socket.c:2406 [inline]
 __sys_sendmsg+0x2b1/0x360 net/socket.c:2439
 do_syscall_64+0x73/0xe0 arch/x86/entry/common.c:359
RIP: 0033:0x443799
Code: Bad RIP value.
RSP: 002b:00007ffe68f74b78 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 0000000000443799
RDX: 0000000000000000 RSI: 00000000200007c0 RDI: 0000000000000004
RBP: 00007ffe68f74b80 R08: 0000000001bbbbbb R09: 0000000001bbbbbb
R10: 0000000001bbbbbb R11: 0000000000000246 R12: 00007ffe68f74b90
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
INFO: NMI handler (nmi_cpu_backtrace_handler) took too long to run: 0.000 msecs

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