Re: [syzbot] INFO: rcu detected stall in sys_recvmmsg

[Paolo Abeni <pabeni@redhat.com>]

On Tue, 2021-09-21 at 17:13 -0700, syzbot wrote:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    1f77990c4b79 Add linux-next specific files for 20210920
> git tree:       linux-next
> console output: https://syzkaller.appspot.com/x/log.txt?x=1383891d300000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=ab1346371f2e6884
> dashboard link: https://syzkaller.appspot.com/bug?extid=3360da629681aa0d22fe
> compiler:       gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1625f1ab300000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=17eb1b3b300000
> 
> The issue was bisected to:
> 
> commit 020250f31c4c75ac7687a673e29c00786582a5f4
> Author: Dmitry Kadashev <dkadashev@gmail.com>
> Date:   Thu Jul 8 06:34:43 2021 +0000
> 
>     namei: make do_linkat() take struct filename
> 
> bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=15f5ef77300000
> final oops:     https://syzkaller.appspot.com/x/report.txt?x=17f5ef77300000
> console output: https://syzkaller.appspot.com/x/log.txt?x=13f5ef77300000
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+3360da629681aa0d22fe@syzkaller.appspotmail.com
> Fixes: 020250f31c4c ("namei: make do_linkat() take struct filename")
> 
> rcu: INFO: rcu_preempt self-detected stall on CPU
> rcu: 	0-...!: (10499 ticks this GP) idle=0af/1/0x4000000000000000 softirq=10678/10678 fqs=1 
> 	(t=10500 jiffies g=13089 q=109)
> rcu: rcu_preempt kthread starved for 10497 jiffies! g13089 f0x0 RCU_GP_WAIT_FQS(5) ->state=0x0 ->cpu=1
> 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:28696 pid:   14 ppid:     2 flags:0x00004000
> Call Trace:
>  context_switch kernel/sched/core.c:4955 [inline]
>  __schedule+0x940/0x26f0 kernel/sched/core.c:6236
>  schedule+0xd3/0x270 kernel/sched/core.c:6315
>  schedule_timeout+0x14a/0x2a0 kernel/time/timer.c:1881
>  rcu_gp_fqs_loop+0x186/0x810 kernel/rcu/tree.c:1955
>  rcu_gp_kthread+0x1de/0x320 kernel/rcu/tree.c:2128
>  kthread+0x405/0x4f0 kernel/kthread.c:327
>  ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295
> rcu: Stack dump where RCU GP kthread last ran:
> Sending NMI from CPU 0 to CPUs 1:
> NMI backtrace for cpu 1
> CPU: 1 PID: 8510 Comm: syz-executor827 Not tainted 5.15.0-rc2-next-20210920-syzkaller #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> RIP: 0010:bytes_is_nonzero mm/kasan/generic.c:84 [inline]
> RIP: 0010:memory_is_nonzero mm/kasan/generic.c:102 [inline]
> RIP: 0010:memory_is_poisoned_n mm/kasan/generic.c:128 [inline]
> RIP: 0010:memory_is_poisoned mm/kasan/generic.c:159 [inline]
> RIP: 0010:check_region_inline mm/kasan/generic.c:180 [inline]
> RIP: 0010:kasan_check_range+0xc8/0x180 mm/kasan/generic.c:189
> Code: 38 00 74 ed 48 8d 50 08 eb 09 48 83 c0 01 48 39 d0 74 7a 80 38 00 74 f2 48 89 c2 b8 01 00 00 00 48 85 d2 75 56 5b 5d 41 5c c3 <48> 85 d2 74 5e 48 01 ea eb 09 48 83 c0 01 48 39 d0 74 50 80 38 00
> RSP: 0018:ffffc9000cd676c8 EFLAGS: 00000283
> RAX: ffffed100e9a110e RBX: ffffed100e9a110f RCX: ffffffff88ea062a
> RDX: 0000000000000001 RSI: 0000000000000008 RDI: ffff888074d08870
> RBP: ffffed100e9a110e R08: 0000000000000001 R09: ffff888074d08877
> R10: ffffed100e9a110e R11: 0000000000000000 R12: ffff888074d08000
> R13: ffff888074d08000 R14: ffff888074d08088 R15: ffff888074d08000
> FS:  0000555556d8e300(0000) GS:ffff8880b9d00000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 0000000020000180 CR3: 0000000068909000 CR4: 00000000001506e0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
>  instrument_atomic_read_write include/linux/instrumented.h:101 [inline]
>  test_and_clear_bit include/asm-generic/bitops/instrumented-atomic.h:83 [inline]
>  mptcp_release_cb+0x14a/0x210 net/mptcp/protocol.c:3016
>  release_sock+0xb4/0x1b0 net/core/sock.c:3204
>  mptcp_wait_data net/mptcp/protocol.c:1770 [inline]
>  mptcp_recvmsg+0xfd1/0x27b0 net/mptcp/protocol.c:2080
>  inet6_recvmsg+0x11b/0x5e0 net/ipv6/af_inet6.c:659
>  sock_recvmsg_nosec net/socket.c:944 [inline]
>  ____sys_recvmsg+0x527/0x600 net/socket.c:2626
>  ___sys_recvmsg+0x127/0x200 net/socket.c:2670
>  do_recvmmsg+0x24d/0x6d0 net/socket.c:2764
>  __sys_recvmmsg net/socket.c:2843 [inline]
>  __do_sys_recvmmsg net/socket.c:2866 [inline]
>  __se_sys_recvmmsg net/socket.c:2859 [inline]
>  __x64_sys_recvmmsg+0x20b/0x260 net/socket.c:2859
>  do_syscall_x64 arch/x86/entry/common.c:50 [inline]
>  do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
>  entry_SYSCALL_64_after_hwframe+0x44/0xae
> RIP: 0033:0x7fc200d2dc39
> Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 41 15 00 00 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 c0 ff ff ff f7 d8 64 89 01 48
> RSP: 002b:00007ffc5758e5a8 EFLAGS: 00000246 ORIG_RAX: 000000000000012b
> RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 00007fc200d2dc39
> RDX: 0000000000000002 RSI: 00000000200017c0 RDI: 0000000000000003
> RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000f0b5ff
> R10: 0000000000000100 R11: 0000000000000246 R12: 0000000000000003
> R13: 00007ffc5758e5d0 R14: 00007ffc5758e5c0 R15: 0000000000000003
> INFO: NMI handler (nmi_cpu_backtrace_handler) took too long to run: 1.444 msecs
> NMI backtrace for cpu 0
> CPU: 0 PID: 8509 Comm: syz-executor827 Not tainted 5.15.0-rc2-next-20210920-syzkaller #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> Call Trace:
>  <IRQ>
>  __dump_stack lib/dump_stack.c:88 [inline]
>  dump_stack_lvl+0xcd/0x134 lib/dump_stack.c:106
>  nmi_cpu_backtrace.cold+0x47/0x144 lib/nmi_backtrace.c:105
>  nmi_trigger_cpumask_backtrace+0x1ae/0x220 lib/nmi_backtrace.c:62
>  trigger_single_cpu_backtrace include/linux/nmi.h:164 [inline]
>  rcu_dump_cpu_stacks+0x25e/0x3f0 kernel/rcu/tree_stall.h:343
>  print_cpu_stall kernel/rcu/tree_stall.h:627 [inline]
>  check_cpu_stall kernel/rcu/tree_stall.h:711 [inline]
>  rcu_pending kernel/rcu/tree.c:3878 [inline]
>  rcu_sched_clock_irq.cold+0x9d/0x746 kernel/rcu/tree.c:2597
>  update_process_times+0x16d/0x200 kernel/time/timer.c:1785
>  tick_sched_handle+0x9b/0x180 kernel/time/tick-sched.c:226
>  tick_sched_timer+0x1b0/0x2d0 kernel/time/tick-sched.c:1428
>  __run_hrtimer kernel/time/hrtimer.c:1685 [inline]
>  __hrtimer_run_queues+0x1c0/0xe50 kernel/time/hrtimer.c:1749
>  hrtimer_interrupt+0x31c/0x790 kernel/time/hrtimer.c:1811
>  local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1086 [inline]
>  __sysvec_apic_timer_interrupt+0x146/0x530 arch/x86/kernel/apic/apic.c:1103
>  sysvec_apic_timer_interrupt+0x8e/0xc0 arch/x86/kernel/apic/apic.c:1097
>  </IRQ>
>  asm_sysvec_apic_timer_interrupt+0x12/0x20 arch/x86/include/asm/idtentry.h:638
> RIP: 0010:lock_release+0x3f1/0x720 kernel/locking/lockdep.c:5633
> Code: 7e 83 f8 01 0f 85 8d 01 00 00 9c 58 f6 c4 02 0f 85 78 01 00 00 48 f7 04 24 00 02 00 00 74 01 fb 48 b8 00 00 00 00 00 fc ff df <48> 01 c5 48 c7 45 00 00 00 00 00 c7 45 08 00 00 00 00 48 8b 84 24
> RSP: 0018:ffffc9000cde7660 EFLAGS: 00000206
> RAX: dffffc0000000000 RBX: 70dbee1ebc366ab9 RCX: ffffc9000cde76b0
> RDX: 1ffff11003a0bc2b RSI: 0000000000000201 RDI: 0000000000000000
> RBP: 1ffff920019bcece R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000001 R11: 0000000000000443 R12: 0000000000000001
> R13: 0000000000000002 R14: ffff88801d05e160 R15: ffff88801d05d700
>  __raw_spin_unlock_bh include/linux/spinlock_api_smp.h:174 [inline]
>  _raw_spin_unlock_bh+0x12/0x30 kernel/locking/spinlock.c:210
>  spin_unlock_bh include/linux/spinlock.h:413 [inline]
>  unlock_sock_fast include/net/sock.h:1644 [inline]
>  unlock_sock_fast include/net/sock.h:1636 [inline]
>  mptcp_subflow_cleanup_rbuf net/mptcp/protocol.c:468 [inline]
>  mptcp_cleanup_rbuf net/mptcp/protocol.c:499 [inline]
>  mptcp_recvmsg+0xb8b/0x27b0 net/mptcp/protocol.c:2027
>  inet6_recvmsg+0x11b/0x5e0 net/ipv6/af_inet6.c:659
>  sock_recvmsg_nosec net/socket.c:944 [inline]
>  ____sys_recvmsg+0x527/0x600 net/socket.c:2626
>  ___sys_recvmsg+0x127/0x200 net/socket.c:2670
>  do_recvmmsg+0x24d/0x6d0 net/socket.c:2764
>  __sys_recvmmsg net/socket.c:2843 [inline]
>  __do_sys_recvmmsg net/socket.c:2866 [inline]
>  __se_sys_recvmmsg net/socket.c:2859 [inline]
>  __x64_sys_recvmmsg+0x20b/0x260 net/socket.c:2859
>  do_syscall_x64 arch/x86/entry/common.c:50 [inline]
>  do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
>  entry_SYSCALL_64_after_hwframe+0x44/0xae
> RIP: 0033:0x7fc200d2dc39
> Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 41 15 00 00 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 c0 ff ff ff f7 d8 64 89 01 48
> RSP: 002b:00007ffc5758e5a8 EFLAGS: 00000246 ORIG_RAX: 000000000000012b
> RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 00007fc200d2dc39
> RDX: 0000000000000002 RSI: 00000000200017c0 RDI: 0000000000000003
> RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000f0b5ff
> R10: 0000000000000100 R11: 0000000000000246 R12: 0000000000000003
> R13: 00007ffc5758e5d0 R14: 00007ffc5758e5c0 R15: 0000000000000003
> ----------------
> Code disassembly (best guess):
>    0:	38 00                	cmp    %al,(%rax)
>    2:	74 ed                	je     0xfffffff1
>    4:	48 8d 50 08          	lea    0x8(%rax),%rdx
>    8:	eb 09                	jmp    0x13
>    a:	48 83 c0 01          	add    $0x1,%rax
>    e:	48 39 d0             	cmp    %rdx,%rax
>   11:	74 7a                	je     0x8d
>   13:	80 38 00             	cmpb   $0x0,(%rax)
>   16:	74 f2                	je     0xa
>   18:	48 89 c2             	mov    %rax,%rdx
>   1b:	b8 01 00 00 00       	mov    $0x1,%eax
>   20:	48 85 d2             	test   %rdx,%rdx
>   23:	75 56                	jne    0x7b
>   25:	5b                   	pop    %rbx
>   26:	5d                   	pop    %rbp
>   27:	41 5c                	pop    %r12
>   29:	c3                   	retq
> * 2a:	48 85 d2             	test   %rdx,%rdx <-- trapping instruction
>   2d:	74 5e                	je     0x8d
>   2f:	48 01 ea             	add    %rbp,%rdx
>   32:	eb 09                	jmp    0x3d
>   34:	48 83 c0 01          	add    $0x1,%rax
>   38:	48 39 d0             	cmp    %rdx,%rax
>   3b:	74 50                	je     0x8d
>   3d:	80 38 00             	cmpb   $0x0,(%rax)
> 
> 
> ---
> This report is generated by a bot. It may contain errors.
> See https://goo.gl/tpsmEJ for more information about syzbot.
> syzbot engineers can be reached at syzkaller@googlegroups.com.
> 
> syzbot will keep track of this issue. See:
> https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
> For information about bisection process see: https://goo.gl/tpsmEJ#bisection
> syzbot can test patches for this issue, for details see:
> https://goo.gl/tpsmEJ#testing-patches

#syz test: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master

for net-next we should likely consider dropping the DATA_READY flag at
all, but that looks too invasive and error prone for a fix
---
diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index dbcebf56798f..6b334f9b6242 100644
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -1759,11 +1759,32 @@ static int mptcp_sendmsg(struct sock *sk,
struct msghdr *msg, size_t len)
 	return copied ? : ret;
 }
 
+static bool __mptcp_move_skbs(struct mptcp_sock *msk);
+
+static void mptcp_update_ready_flag(struct sock *sk)
+{
+	struct mptcp_sock *msk = mptcp_sk(sk);
+
+	if (skb_queue_empty_lockless(&sk->sk_receive_queue) &&
+	    skb_queue_empty(&msk->receive_queue)) {
+		/* entire backlog drained, clear DATA_READY. */
+		clear_bit(MPTCP_DATA_READY, &msk->flags);
+
+		/* .. race-breaker: ssk might have gotten new data
+		 * after last __mptcp_move_skbs() returned false.
+		 */
+		if (unlikely(__mptcp_move_skbs(msk)))
+			set_bit(MPTCP_DATA_READY, &msk->flags);
+	}
+}
+
 static void mptcp_wait_data(struct sock *sk, long *timeo)
 {
 	DEFINE_WAIT_FUNC(wait, woken_wake_function);
 	struct mptcp_sock *msk = mptcp_sk(sk);
 
+	mptcp_update_ready_flag(sk);
+
 	add_wait_queue(sk_sleep(sk), &wait);
 	sk_set_bit(SOCKWQ_ASYNC_WAITDATA, sk);
 
@@ -2080,17 +2101,7 @@ static int mptcp_recvmsg(struct sock *sk, struct
msghdr *msg, size_t len,
 		mptcp_wait_data(sk, &timeo);
 	}
 
-	if (skb_queue_empty_lockless(&sk->sk_receive_queue) &&
-	    skb_queue_empty(&msk->receive_queue)) {
-		/* entire backlog drained, clear DATA_READY. */
-		clear_bit(MPTCP_DATA_READY, &msk->flags);
-
-		/* .. race-breaker: ssk might have gotten new data
-		 * after last __mptcp_move_skbs() returned false.
-		 */
-		if (unlikely(__mptcp_move_skbs(msk)))
-			set_bit(MPTCP_DATA_READY, &msk->flags);
-	}
+	mptcp_update_ready_flag(sk);
 
 out_err:
 	if (cmsg_flags && copied >= 0) {