Re: INFO: rcu detected stall in __schedule

From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
To: syzbot <syzbot+f16b3e3512a1e3c1d1f6@syzkaller.appspotmail.com>,
	syzkaller-bugs@googlegroups.com, dvyukov@google.com
Cc: linux-kernel@vger.kernel.org, linux-ppp@vger.kernel.org,
	netdev@vger.kernel.org, paulus@samba.org
Subject: Re: INFO: rcu detected stall in __schedule
Date: Thu, 3 May 2018 14:45:24 +0900	[thread overview]
Message-ID: <1356afb7-80cf-d9d9-c282-e4e819807376@I-love.SAKURA.ne.jp> (raw)
In-Reply-To: <000000000000d2fe62056b3ccca5@google.com>

I'm not sure whether this is a PPP bug.

As of uptime = 484, RCU says that it stalled for 125 seconds.

----------
[  484.407032] INFO: rcu_sched self-detected stall on CPU
[  484.412488] 	0-...!: (125000 ticks this GP) idle=f3e/1/4611686018427387906 softirq=112858/112858 fqs=0 
[  484.422300] 	 (t=125000 jiffies g=61626 c=61625 q=1534)
[  484.427663] rcu_sched kthread starved for 125000 jiffies! g61626 c61625 f0x0 RCU_GP_WAIT_FQS(3) ->state=0x402 ->cpu=0
----------

484 - 125 = 359, which was about to start SND related fuzzing in that log.

----------
2033/05/18 03:36:31 executing program 1:
r0 = socket(0x40000a, 0x5, 0x7)
setsockopt$inet_int(r0, 0x0, 0x18, &(0x7f0000000000)=0x200, 0x4)
bind$inet6(r0, &(0x7f00000000c0)={0xa, 0x0, 0x0, @loopback={0x0, 0x1}}, 0x1c)
perf_event_open(&(0x7f0000000040)={0x2, 0x70, 0x3e5}, 0x0, 0xffffffffffffffff, 0xffffffffffffffff, 0x0)
timer_create(0x0, &(0x7f00000001c0)={0x0, 0x15, 0x0, @thr={&(0x7f0000000440), &(0x7f0000000540)}}, &(0x7f0000000200))
timer_getoverrun(0x0)
perf_event_open(&(0x7f000025c000)={0x2, 0x78, 0x3e3}, 0x0, 0x0, 0xffffffffffffffff, 0x0)
r1 = syz_open_dev$sndctrl(&(0x7f0000000200)='/dev/snd/controlC#\x00', 0x2, 0x0)
perf_event_open(&(0x7f0000001000)={0x0, 0x70, 0x0, 0x0, 0x0, 0x0, 0x0, 0x8ce, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x7, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0xfffffffffffffff8, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, @perf_bp={&(0x7f0000005000), 0x2}, 0x1000000000c}, 0x0, 0x0, 0xffffffffffffffff, 0x0)
ioctl$SNDRV_CTL_IOCTL_SUBSCRIBE_EVENTS(r1, 0xc0045516, &(0x7f00000000c0)=0x1)
r2 = syz_open_dev$sndpcmp(&(0x7f0000000100)='/dev/snd/pcmC#D#p\x00', 0x1, 0x4000)
ioctl$SNDRV_SEQ_IOCTL_GET_QUEUE_CLIENT(r2, 0xc04c5349, &(0x7f0000000240)={0x200, 0xfffffffffffffcdc, 0x1})
syz_open_dev$tun(&(0x7f00000003c0)='/dev/net/tun\x00', 0x0, 0x20402)
ioctl$SNDRV_CTL_IOCTL_PVERSION(r1, 0xc1105517, &(0x7f0000001000)=""/250)
ioctl$SNDRV_CTL_IOCTL_SUBSCRIBE_EVENTS(r1, 0xc0045516, &(0x7f0000000000))

2033/05/18 03:36:31 executing program 4:
syz_emit_ethernet(0x3e, &(0x7f00000000c0)={@broadcast=[0xff, 0xff, 0xff, 0xff, 0xff, 0xff], @empty=[0x0, 0x0, 0xb00000000000000], [], {@ipv4={0x800, {{0x5, 0x4, 0x0, 0x0, 0x30, 0x0, 0x0, 0x0, 0x1, 0x0, @remote={0xac, 0x14, 0x14, 0xbb}, @dev={0xac, 0x14, 0x14}}, @icmp=@parameter_prob={0x5, 0x4, 0x0, 0x0, 0x0, 0x0, {0x5, 0x4, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, @local={0xac, 0x223, 0x14, 0xaa}, @dev={0xac, 0x14, 0x14}}}}}}}, &(0x7f0000000000)={0x0, 0x2, [0x0, 0x2e6]})

2033/05/18 03:36:31 executing program 1:
r0 = socket$pppoe(0x18, 0x1, 0x0)
connect$pppoe(r0, &(0x7f00000000c0)={0x18, 0x0, {0x1, @broadcast=[0xff, 0xff, 0xff, 0xff, 0xff, 0xff], 'ip6_vti0\x00'}}, 0x1e)
r1 = socket(0x3, 0xb, 0x80000001)
setsockopt$inet_sctp6_SCTP_ADAPTATION_LAYER(r1, 0x84, 0x7, &(0x7f0000000100)={0x2}, 0x4)
ioctl$sock_inet_SIOCGIFADDR(r0, 0x8915, &(0x7f0000000040)={'veth1_to_bridge\x00', {0x2, 0x4e21}})
r2 = syz_open_dev$admmidi(&(0x7f0000000000)='/dev/admmidi#\x00', 0x6, 0x8000)
setsockopt$SO_VM_SOCKETS_BUFFER_MAX_SIZE(r2, 0x28, 0x2, &(0x7f0000000080)=0xffffffffffffff00, 0x8)

[  359.306427] snd_virmidi snd_virmidi.0: control 112:0:0:�\b:0 is already present
----------