[Android 6.1] BUG: soft lockup in tc_modify_qdisc

Hello,

syzbot found the following issue on:

HEAD commit: 35361bdac25a Merge "Merge tag 'android14-6.1.43_r00' into ..
git tree: android14-6.1
console+strace: https://syzkaller.appspot.com/x/log.txt?x=15955149680000
kernel config: https://syzkaller.appspot.com/x/.config?x=e9500dd6486f6367
dashboard link: https://syzkaller.appspot.com/bug?extid=e4d258d1bfd27e45e816
compiler: Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=1601dd49680000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=1647790d680000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/fdc9fa9f7815/disk-35361bda.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/a83f1ec86c19/vmlinux-35361bda.xz
kernel image: https://storage.googleapis.com/syzbot-assets/16fef5ad5486/bzImage-35361bda.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: [email protected]

RBP: 0000000000000000 R08: 0000000000000000 R09: 0000555555abb610
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
</TASK>
watchdog: BUG: soft lockup - CPU#1 stuck for 225s! [syz-executor192:297]
Modules linked in:
CPU: 1 PID: 297 Comm: syz-executor192 Not tainted 6.1.43-syzkaller-00235-g35361bdac25a #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/06/2023
RIP: 0010:pv_wait_head_or_lock kernel/locking/qspinlock_paravirt.h:434 [inline]
RIP: 0010:__pv_queued_spin_lock_slowpath+0x5e0/0xda0 kernel/locking/qspinlock.c:511
Code: 48 8b 44 24 10 c6 00 00 48 8b 44 24 18 0f b6 04 10 84 c0 0f 85 48 01 00 00 48 8b 44 24 08 c6 00 01 bb 00 80 ff ff eb 06 f3 90 <ff> c3 74 5d 41 0f b6 04 14 84 c0 75 36 41 80 3f 00 75 eb 4c 89 ff
RSP: 0018:ffffc90000e76ca0 EFLAGS: 00000206
RAX: 0000000000000000 RBX: 00000000fffffb75 RCX: ffffffff84fbdbec
RDX: dffffc0000000000 RSI: 0000000000000003 RDI: ffffffff873a54ac
RBP: ffffc90000e76d90 R08: dffffc0000000000 R09: fffffbfff0e74a96
R10: 0000000000000000 R11: dffffc0000000001 R12: 1ffffffff0e74a95
R13: ffff88823fe92b00 R14: 1ffff1103ee20001 R15: ffffffff873a54ac
FS: 0000555555aba380(0000) GS:ffff8881f7100000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000000000045b630 CR3: 0000000120c72000 CR4: 00000000003506a0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
<IRQ>
</IRQ>
<TASK>
pv_queued_spin_lock_slowpath arch/x86/include/asm/paravirt.h:591 [inline]
queued_spin_lock_slowpath arch/x86/include/asm/qspinlock.h:51 [inline]
queued_spin_lock include/asm-generic/qspinlock.h:114 [inline]
do_raw_spin_lock include/linux/spinlock.h:186 [inline]
__raw_spin_lock_bh include/linux/spinlock_api_smp.h:127 [inline]
_raw_spin_lock_bh+0x139/0x1b0 kernel/locking/spinlock.c:178
spin_lock_bh include/linux/spinlock.h:355 [inline]
get_dist_table+0x215/0x2e0 net/sched/sch_netem.c:798
netem_change+0x9ec/0x20b0 net/sched/sch_netem.c:985
netem_init+0x5b/0xb0 net/sched/sch_netem.c:1072
qdisc_create+0x889/0x1160 net/sched/sch_api.c:1314
tc_modify_qdisc+0x8d0/0x19c0
rtnetlink_rcv_msg+0x9a5/0xca0 net/core/rtnetlink.c:6103
netlink_rcv_skb+0x1cd/0x410 net/netlink/af_netlink.c:2525
rtnetlink_rcv+0x1c/0x20 net/core/rtnetlink.c:6121
netlink_unicast_kernel net/netlink/af_netlink.c:1328 [inline]
netlink_unicast+0x8ee/0xad0 net/netlink/af_netlink.c:1354
netlink_sendmsg+0xa15/0xd30 net/netlink/af_netlink.c:1903
sock_sendmsg_nosec net/socket.c:716 [inline]
sock_sendmsg net/socket.c:736 [inline]
____sys_sendmsg+0x5dc/0x9d0 net/socket.c:2482
___sys_sendmsg net/socket.c:2536 [inline]
__sys_sendmsg+0x2a9/0x390 net/socket.c:2565
__do_sys_sendmsg net/socket.c:2574 [inline]
__se_sys_sendmsg net/socket.c:2572 [inline]
__x64_sys_sendmsg+0x7f/0x90 net/socket.c:2572
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x3d/0xb0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x63/0xcd
RIP: 0033:0x7f80f269d109
Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 21 18 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 b8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffd3b1676e8 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 00007f80f269d109
RDX: 0000000000000000 RSI: 00000000200002c0 RDI: 0000000000000004
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000555555abb610
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
</TASK>


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syzbot has bisected this issue to:

commit b2e2f9c0939f990dc5daca0838c3a4456f0ba345
Author: Eric Dumazet <[email protected]>
Date: Tue Jun 20 18:44:25 2023 +0000

sch_netem: acquire qdisc lock in netem_change()

bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=1553ee0d680000
start commit: 35361bdac25a Merge "Merge tag 'android14-6.1.43_r00' into ..
git tree: android14-6.1
final oops: https://syzkaller.appspot.com/x/report.txt?x=1753ee0d680000
console output: https://syzkaller.appspot.com/x/log.txt?x=1353ee0d680000
Reported-by: [email protected]
Fixes: b2e2f9c0939f ("sch_netem: acquire qdisc lock in netem_change()")

For information about bisection process see: https://goo.gl/tpsmEJ#bisection

syzbot suspects this issue was fixed by commit:

commit 4346a66ad19876663e46d57c85dac5958f227033
Author: Eric Dumazet <[email protected]>
Date: Thu Jun 22 18:15:03 2023 +0000

sch_netem: fix issues in netem_change() vs get_dist_table()

bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=129970cee80000
start commit: df6e6fc38f4f UPSTREAM: PM: hibernate: Fix copying the zero..
git tree: android14-6.1
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=164e158ae80000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=16bf9378e80000

If the result looks correct, please mark the issue as fixed by replying with:

#syz fix: sch_netem: fix issues in netem_change() vs get_dist_table()

Auto-closing this bug as obsolete.
No recent activity, existing reproducers are no longer triggering the issue.