Re: [syzbot] [net?] INFO: task hung in nsim_create (2)

From: Eric Dumazet
Date: Thu Jul 25 2024 - 04:31:27 EST

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In reply to: David Wei: "Re: [syzbot] [net?] INFO: task hung in nsim_create (2)"
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On Wed, Jul 24, 2024 at 11:39 PM David Wei <dw@xxxxxxxxxxx> wrote:
>
> On 2024-07-24 11:28, Eric Dumazet wrote:
> > On Wed, Jul 24, 2024 at 8:05 PM syzbot
> > <syzbot+90fd70a665715bd10258@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
> >>
> >> Hello,
> >>
> >> syzbot found the following issue on:
> >>
> >> HEAD commit: 68b59730459e Merge tag 'perf-tools-for-v6.11-2024-07-16' o..
> >> git tree: upstream
> >> console output: https://syzkaller.appspot.com/x/log.txt?x=13e0a195980000
> >> kernel config: https://syzkaller.appspot.com/x/.config?x=b6230d83d52af231
> >> dashboard link: https://syzkaller.appspot.com/bug?extid=90fd70a665715bd10258
> >> compiler: Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
> >>
> >> Unfortunately, I don't have any reproducer for this issue yet.
> >>
> >> Downloadable assets:
> >> disk image: https://storage.googleapis.com/syzbot-assets/2ed0d621f118/disk-68b59730.raw.xz
> >> vmlinux: https://storage.googleapis.com/syzbot-assets/36b453c7acac/vmlinux-68b59730.xz
> >> kernel image: https://storage.googleapis.com/syzbot-assets/069a896ef41a/bzImage-68b59730.xz
> >>
> >> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> >> Reported-by: syzbot+90fd70a665715bd10258@xxxxxxxxxxxxxxxxxxxxxxxxx
> >>
> >> INFO: task kworker/u8:5:570 blocked for more than 143 seconds.
> >> Not tainted 6.10.0-syzkaller-08280-g68b59730459e #0
> >> "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> >> task:kworker/u8:5 state:D stack:20528 pid:570 tgid:570 ppid:2 flags:0x00004000
> >> Workqueue: netns cleanup_net
> >> Call Trace:
> >> <TASK>
> >> context_switch kernel/sched/core.c:5188 [inline]
> >> __schedule+0x1800/0x4a60 kernel/sched/core.c:6529
> >> __schedule_loop kernel/sched/core.c:6606 [inline]
> >> schedule+0x14b/0x320 kernel/sched/core.c:6621
> >> schedule_preempt_disabled+0x13/0x30 kernel/sched/core.c:6678
> >> __mutex_lock_common kernel/locking/mutex.c:684 [inline]
> >> __mutex_lock+0x6a4/0xd70 kernel/locking/mutex.c:752
>
> This is rtnl_lock(). From stack trace looks like this is triggered when
> removing the ns that a netdevsim is in. This calls into
> devlink_pernet_pre_exit() which reloads a devlink (and its associated
> netdevsim) into the init ns.
>
> >> nsim_init_netdevsim drivers/net/netdevsim/netdev.c:678 [inline]
> >> nsim_create+0x408/0x890 drivers/net/netdevsim/netdev.c:750
> >> __nsim_dev_port_add+0x6c0/0xae0 drivers/net/netdevsim/dev.c:1390
> >> nsim_dev_port_add_all drivers/net/netdevsim/dev.c:1446 [inline]
> >> nsim_dev_reload_create drivers/net/netdevsim/dev.c:1498 [inline]
> >> nsim_dev_reload_up+0x69b/0x8e0 drivers/net/netdevsim/dev.c:985
> >> devlink_reload+0x478/0x870 net/devlink/dev.c:474
> >> devlink_pernet_pre_exit+0x1f3/0x440 net/devlink/core.c:509
> >> ops_pre_exit_list net/core/net_namespace.c:163 [inline]
> >> cleanup_net+0x615/0xcc0 net/core/net_namespace.c:620
> >> process_one_work kernel/workqueue.c:3231 [inline]
> >> process_scheduled_works+0xa2c/0x1830 kernel/workqueue.c:3312
> >> worker_thread+0x86d/0xd40 kernel/workqueue.c:3390
> >> kthread+0x2f0/0x390 kernel/kthread.c:389
> >> ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:147
> >> ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244
> >> </TASK>
> >> INFO: task kworker/u8:7:2410 blocked for more than 144 seconds.
> >> Not tainted 6.10.0-syzkaller-08280-g68b59730459e #0
> >> "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> >> task:kworker/u8:7 state:D stack:23312 pid:2410 tgid:2410 ppid:2 flags:0x00004000
> >> Workqueue: ipv6_addrconf addrconf_dad_work
> >> Call Trace:
> >> <TASK>
> >> context_switch kernel/sched/core.c:5188 [inline]
> >> __schedule+0x1800/0x4a60 kernel/sched/core.c:6529
> >> __schedule_loop kernel/sched/core.c:6606 [inline]
> >> schedule+0x14b/0x320 kernel/sched/core.c:6621
> >> schedule_preempt_disabled+0x13/0x30 kernel/sched/core.c:6678
> >> __mutex_lock_common kernel/locking/mutex.c:684 [inline]
> >> __mutex_lock+0x6a4/0xd70 kernel/locking/mutex.c:752
>
> This is rtnl_lock() as well. Work is scheduled on a wq in
> ipv6_add_addr() but not sure what the caller of this is. Can this be
> called from sysfs?
>
> >> addrconf_dad_work+0xd0/0x16f0 net/ipv6/addrconf.c:4194
> >> process_one_work kernel/workqueue.c:3231 [inline]
> >> process_scheduled_works+0xa2c/0x1830 kernel/workqueue.c:3312
> >> worker_thread+0x86d/0xd40 kernel/workqueue.c:3390
> >> kthread+0x2f0/0x390 kernel/kthread.c:389
> >> ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:147
> >> ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244
> >> </TASK>
> >> INFO: task dhcpcd:4769 blocked for more than 145 seconds.
> >> Not tainted 6.10.0-syzkaller-08280-g68b59730459e #0
> >> "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> >> task:dhcpcd state:D
> >> stack:20384 pid:4769 tgid:4769 ppid:4768 flags:0x00000002
> >> Call Trace:
> >> <TASK>
> >> context_switch kernel/sched/core.c:5188 [inline]
> >> __schedule+0x1800/0x4a60 kernel/sched/core.c:6529
> >> __schedule_loop kernel/sched/core.c:6606 [inline]
> >> schedule+0x14b/0x320 kernel/sched/core.c:6621
> >> schedule_preempt_disabled+0x13/0x30 kernel/sched/core.c:6678
> >> __mutex_lock_common kernel/locking/mutex.c:684 [inline]
> >> __mutex_lock+0x6a4/0xd70 kernel/locking/mutex.c:752
> >> rtnl_lock net/core/rtnetlink.c:79 [inline]
> >> rtnetlink_rcv_msg+0x6e6/0xcf0 net/core/rtnetlink.c:6644
> >> netlink_rcv_skb+0x1e3/0x430 net/netlink/af_netlink.c:2550
> >> netlink_unicast_kernel net/netlink/af_netlink.c:1331 [inline]
> >> netlink_unicast+0x7f0/0x990 net/netlink/af_netlink.c:1357
> >> netlink_sendmsg+0x8e4/0xcb0 net/netlink/af_netlink.c:1901
> >> sock_sendmsg_nosec net/socket.c:730 [inline]
> >> __sock_sendmsg+0x221/0x270 net/socket.c:745
> >> ____sys_sendmsg+0x525/0x7d0 net/socket.c:2597
> >> ___sys_sendmsg net/socket.c:2651 [inline]
> >> __sys_sendmsg+0x2b0/0x3a0 net/socket.c:2680
> >> do_syscall_x64 arch/x86/entry/common.c:52 [inline]
> >> do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
> >> entry_SYSCALL_64_after_hwframe+0x77/0x7f
> >> RIP: 0033:0x7f9d6db7da4b
> >> RSP: 002b:00007ffd2f22e8c8 EFLAGS: 00000246
> >> ORIG_RAX: 000000000000002e
> >> RAX: ffffffffffffffda RBX: 00007f9d6daa56c0 RCX: 00007f9d6db7da4b
> >> RDX: 0000000000000000 RSI: 00007ffd2f242a78 RDI: 0000000000000005
> >> RBP: 0000000000000005 R08: 0000000000000000 R09: 00007ffd2f242a78
> >> R10: 0000000000000000 R11: 0000000000000246 R12: ffffffffffffffff
> >> R13: 00007ffd2f242a78 R14: 0000000000000030 R15: 0000000000000001
> >> </TASK>
> >> INFO: task udevd:5105 blocked for more than 146 seconds.
> >> Not tainted 6.10.0-syzkaller-08280-g68b59730459e #0
> >> "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> >> task:udevd state:D
> >> stack:24864 pid:5105 tgid:5105 ppid:4555 flags:0x00000002
> >> Call Trace:
> >> <TASK>
> >> context_switch kernel/sched/core.c:5188 [inline]
> >> __schedule+0x1800/0x4a60 kernel/sched/core.c:6529
> >> __schedule_loop kernel/sched/core.c:6606 [inline]
> >> schedule+0x14b/0x320 kernel/sched/core.c:6621
> >> schedule_preempt_disabled+0x13/0x30 kernel/sched/core.c:6678
> >> __mutex_lock_common kernel/locking/mutex.c:684 [inline]
> >> __mutex_lock+0x6a4/0xd70 kernel/locking/mutex.c:752
>
> This one is taking dev->mutex which is separate to rtnl_mutex. Not sure
> why this would be blocked too?
>
> >> device_lock include/linux/device.h:1009 [inline]
> >> uevent_show+0x17d/0x340 drivers/base/core.c:2743
> >> dev_attr_show+0x55/0xc0 drivers/base/core.c:2437
> >> sysfs_kf_seq_show+0x331/0x4c0 fs/sysfs/file.c:59
> >> seq_read_iter+0x445/0xd60 fs/seq_file.c:230
> >> new_sync_read fs/read_write.c:395 [inline]
> >> vfs_read+0x9bd/0xbc0 fs/read_write.c:476
> >> ksys_read+0x1a0/0x2c0 fs/read_write.c:619
> >> do_syscall_x64 arch/x86/entry/common.c:52 [inline]
> >> do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
> >> entry_SYSCALL_64_after_hwframe+0x77/0x7f
> >> RIP: 0033:0x7fda18b16b6a
> >> RSP: 002b:00007ffcf336bed8 EFLAGS: 00000246
> >> ORIG_RAX: 0000000000000000
> >> RAX: ffffffffffffffda RBX: 00005588202d8730 RCX: 00007fda18b16b6a
> >> RDX: 0000000000001000 RSI: 0000558820307980 RDI: 0000000000000008
> >> RBP: 00005588202d8730 R08: 0000000000000008 R09: 0000000000000008
> >> R10: 000000000000010f R11: 0000000000000246 R12: 0000000000000000
> >> R13: 0000000000003fff R14: 00007ffcf336c3b8 R15: 000000000000000a
> >> </TASK>
> >> INFO: task syz-executor:5304 blocked for more than 147 seconds.
> >> Not tainted 6.10.0-syzkaller-08280-g68b59730459e #0
> >> "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> >> task:syz-executor state:D stack:20216 pid:5304 tgid:5304 ppid:1 flags:0x00004006
> >> Call Trace:
> >> <TASK>
> >> context_switch kernel/sched/core.c:5188 [inline]
> >> __schedule+0x1800/0x4a60 kernel/sched/core.c:6529
> >> __schedule_loop kernel/sched/core.c:6606 [inline]
> >> schedule+0x14b/0x320 kernel/sched/core.c:6621
> >> schedule_preempt_disabled+0x13/0x30 kernel/sched/core.c:6678
> >> __mutex_lock_common kernel/locking/mutex.c:684 [inline]
> >> __mutex_lock+0x6a4/0xd70 kernel/locking/mutex.c:752
> >> nsim_destroy+0x71/0x5c0 drivers/net/netdevsim/netdev.c:773
> >> __nsim_dev_port_del+0x14b/0x1b0 drivers/net/netdevsim/dev.c:1425
> >> nsim_dev_port_del_all drivers/net/netdevsim/dev.c:1437 [inline]
> >> nsim_dev_reload_destroy+0x28a/0x490 drivers/net/netdevsim/dev.c:1658
> >> nsim_drv_remove+0x58/0x160 drivers/net/netdevsim/dev.c:1673
> >> device_remove drivers/base/dd.c:566 [inline]
> >> __device_release_driver drivers/base/dd.c:1270 [inline]
> >> device_release_driver_internal+0x4a9/0x7c0 drivers/base/dd.c:1293
> >> bus_remove_device+0x34f/0x420 drivers/base/bus.c:574
> >> device_del+0x57a/0x9b0 drivers/base/core.c:3868
> >> device_unregister+0x20/0xc0 drivers/base/core.c:3909
> >> nsim_bus_dev_del drivers/net/netdevsim/bus.c:462 [inline]
>
> This takes a nsim_bus_dev_list_lock in netdevsim/bus.c. When I wrote
> this I was careful to ensure the mutexes were nested correctly.
>
> The rest of the stack traces are all rtnl_lock.
>
> >> del_device_store+0x363/0x480 drivers/net/netdevsim/bus.c:226
> >> kernfs_fop_write_iter+0x3a1/0x500 fs/kernfs/file.c:334
> >> new_sync_write fs/read_write.c:497 [inline]
> >> vfs_write+0xa72/0xc90 fs/read_write.c:590
> >> ksys_write+0x1a0/0x2c0 fs/read_write.c:643
> >> do_syscall_x64 arch/x86/entry/common.c:52 [inline]
> >> do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
> >> entry_SYSCALL_64_after_hwframe+0x77/0x7f
> >> RIP: 0033:0x7f9e2b3746df
> >> RSP: 002b:00007f9e2b62f220 EFLAGS: 00000293
> >> ORIG_RAX: 0000000000000001
> >> RAX: ffffffffffffffda RBX: 0000000000000005 RCX: 00007f9e2b3746df
> >> RDX: 0000000000000001 RSI: 00007f9e2b62f270 RDI: 0000000000000005
> >> RBP: 00007f9e2b3e45b2 R08: 0000000000000000 R09: 00007f9e2b62f077
> >> R10: 0000000000000000 R11: 0000000000000293 R12: 0000000000000001
> >> R13: 00007f9e2b62f270 R14: 00007f9e2c034620 R15: 0000000000000003
> >> </TASK>
> >> INFO: task syz-executor:5325 blocked for more than 148 seconds.
> >> Not tainted 6.10.0-syzkaller-08280-g68b59730459e #0
> >> "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> >> task:syz-executor state:D
> >> stack:21104 pid:5325 tgid:5325 ppid:1 flags:0x00000004
> >> Call Trace:
> >> <TASK>
> >> context_switch kernel/sched/core.c:5188 [inline]
> >> __schedule+0x1800/0x4a60 kernel/sched/core.c:6529
> >> __schedule_loop kernel/sched/core.c:6606 [inline]
> >> schedule+0x14b/0x320 kernel/sched/core.c:6621
> >> schedule_preempt_disabled+0x13/0x30 kernel/sched/core.c:6678
> >> __mutex_lock_common kernel/locking/mutex.c:684 [inline]
> >> __mutex_lock+0x6a4/0xd70 kernel/locking/mutex.c:752
> >> rtnl_lock net/core/rtnetlink.c:79 [inline]
> >> rtnetlink_rcv_msg+0x6e6/0xcf0 net/core/rtnetlink.c:6644
> >> netlink_rcv_skb+0x1e3/0x430 net/netlink/af_netlink.c:2550
> >> netlink_unicast_kernel net/netlink/af_netlink.c:1331 [inline]
> >> netlink_unicast+0x7f0/0x990 net/netlink/af_netlink.c:1357
> >> netlink_sendmsg+0x8e4/0xcb0 net/netlink/af_netlink.c:1901
> >> sock_sendmsg_nosec net/socket.c:730 [inline]
> >> __sock_sendmsg+0x221/0x270 net/socket.c:745
> >> __sys_sendto+0x3a4/0x4f0 net/socket.c:2204
> >> __do_sys_sendto net/socket.c:2216 [inline]
> >> __se_sys_sendto net/socket.c:2212 [inline]
> >> __x64_sys_sendto+0xde/0x100 net/socket.c:2212
> >> do_syscall_x64 arch/x86/entry/common.c:52 [inline]
> >> do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
> >> entry_SYSCALL_64_after_hwframe+0x77/0x7f
> >> RIP: 0033:0x7f1d9e3778ec
> >> RSP: 002b:00007f1d9e62f630 EFLAGS: 00000293
> >> ORIG_RAX: 000000000000002c
> >> RAX: ffffffffffffffda RBX: 00007f1d9f034620 RCX: 00007f1d9e3778ec
> >> RDX: 0000000000000020 RSI: 00007f1d9f034670 RDI: 0000000000000003
> >> RBP: 0000000000000000 R08: 00007f1d9e62f684 R09: 000000000000000c
> >> R10: 0000000000000000 R11: 0000000000000293 R12: 0000000000000003
> >> R13: 0000000000000000 R14: 00007f1d9f034670 R15: 0000000000000000
> >> </TASK>
> >> INFO: task syz-executor:5383 blocked for more than 149 seconds.
> >> Not tainted 6.10.0-syzkaller-08280-g68b59730459e #0
> >> "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> >> task:syz-executor state:D
> >> stack:21728 pid:5383 tgid:5383 ppid:1 flags:0x00000004
> >> Call Trace:
> >> <TASK>
> >> context_switch kernel/sched/core.c:5188 [inline]
> >> __schedule+0x1800/0x4a60 kernel/sched/core.c:6529
> >> __schedule_loop kernel/sched/core.c:6606 [inline]
> >> schedule+0x14b/0x320 kernel/sched/core.c:6621
> >> schedule_preempt_disabled+0x13/0x30 kernel/sched/core.c:6678
> >> __mutex_lock_common kernel/locking/mutex.c:684 [inline]
> >> __mutex_lock+0x6a4/0xd70 kernel/locking/mutex.c:752
> >> rtnl_lock net/core/rtnetlink.c:79 [inline]
> >> rtnetlink_rcv_msg+0x6e6/0xcf0 net/core/rtnetlink.c:6644
> >> netlink_rcv_skb+0x1e3/0x430 net/netlink/af_netlink.c:2550
> >> netlink_unicast_kernel net/netlink/af_netlink.c:1331 [inline]
> >> netlink_unicast+0x7f0/0x990 net/netlink/af_netlink.c:1357
> >> netlink_sendmsg+0x8e4/0xcb0 net/netlink/af_netlink.c:1901
> >> sock_sendmsg_nosec net/socket.c:730 [inline]
> >> __sock_sendmsg+0x221/0x270 net/socket.c:745
> >> __sys_sendto+0x3a4/0x4f0 net/socket.c:2204
> >> __do_sys_sendto net/socket.c:2216 [inline]
> >> __se_sys_sendto net/socket.c:2212 [inline]
> >> __x64_sys_sendto+0xde/0x100 net/socket.c:2212
> >> do_syscall_x64 arch/x86/entry/common.c:52 [inline]
> >> do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
> >> entry_SYSCALL_64_after_hwframe+0x77/0x7f
> >> RIP: 0033:0x7f4baeb778ec
> >> RSP: 002b:00007f4baee2f6b0 EFLAGS: 00000293 ORIG_RAX: 000000000000002c
> >> RAX: ffffffffffffffda RBX: 00007f4baf834620 RCX: 00007f4baeb778ec
> >> RDX: 000000000000003c RSI: 00007f4baf834670 RDI: 0000000000000003
> >> RBP: 0000000000000000 R08: 00007f4baee2f704 R09: 000000000000000c
> >> R10: 0000000000000000 R11: 0000000000000293 R12: 0000000000000003
> >> R13: 0000000000000000 R14: 00007f4baf834670 R15: 0000000000000000
> >> </TASK>
> >> INFO: task syz.3.62:5420 blocked for more than 150 seconds.
> >> Not tainted 6.10.0-syzkaller-08280-g68b59730459e #0
> >> "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> >> task:syz.3.62 state:D stack:22288 pid:5420 tgid:5419 ppid:5118 flags:0x00004006
> >> Call Trace:
> >> <TASK>
> >> context_switch kernel/sched/core.c:5188 [inline]
> >> __schedule+0x1800/0x4a60 kernel/sched/core.c:6529
> >> __schedule_loop kernel/sched/core.c:6606 [inline]
> >> schedule+0x14b/0x320 kernel/sched/core.c:6621
> >> schedule_preempt_disabled+0x13/0x30 kernel/sched/core.c:6678
> >> __mutex_lock_common kernel/locking/mutex.c:684 [inline]
> >> __mutex_lock+0x6a4/0xd70 kernel/locking/mutex.c:752
> >> netdev_wait_allrefs_any net/core/dev.c:10622 [inline]
> >> netdev_run_todo+0x7b2/0x1000 net/core/dev.c:10741
> >> rtnl_unlock net/core/rtnetlink.c:152 [inline]
> >> rtnetlink_rcv_msg+0x748/0xcf0 net/core/rtnetlink.c:6648
> >> netlink_rcv_skb+0x1e3/0x430 net/netlink/af_netlink.c:2550
> >> netlink_unicast_kernel net/netlink/af_netlink.c:1331 [inline]
> >> netlink_unicast+0x7f0/0x990 net/netlink/af_netlink.c:1357
> >> netlink_sendmsg+0x8e4/0xcb0 net/netlink/af_netlink.c:1901
> >> sock_sendmsg_nosec net/socket.c:730 [inline]
> >> __sock_sendmsg+0x221/0x270 net/socket.c:745
> >> ____sys_sendmsg+0x525/0x7d0 net/socket.c:2597
> >> ___sys_sendmsg net/socket.c:2651 [inline]
> >> __sys_sendmsg+0x2b0/0x3a0 net/socket.c:2680
> >> do_syscall_x64 arch/x86/entry/common.c:52 [inline]
> >> do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
> >> entry_SYSCALL_64_after_hwframe+0x77/0x7f
> >> RIP: 0033:0x7f5b41f75b59
> >> RSP: 002b:00007f5b42cf2048 EFLAGS: 00000246
> >> ORIG_RAX: 000000000000002e
> >> RAX: ffffffffffffffda RBX: 00007f5b42105f60 RCX: 00007f5b41f75b59
> >> RDX: 0000000000000000 RSI: 0000000020000140 RDI: 0000000000000006
> >> RBP: 00007f5b41fe4e5d R08: 0000000000000000 R09: 0000000000000000
> >> R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
> >> R13: 000000000000000b R14: 00007f5b42105f60 R15: 00007f5b4222fa78
> >> </TASK>
> >> INFO: task syz-executor:5430 blocked for more than 151 seconds.
> >> Not tainted 6.10.0-syzkaller-08280-g68b59730459e #0
> >> "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> >> task:syz-executor state:D
> >> stack:25264 pid:5430 tgid:5430 ppid:1 flags:0x00004004
> >> Call Trace:
> >> <TASK>
> >> context_switch kernel/sched/core.c:5188 [inline]
> >> __schedule+0x1800/0x4a60 kernel/sched/core.c:6529
> >> __schedule_loop kernel/sched/core.c:6606 [inline]
> >> schedule+0x14b/0x320 kernel/sched/core.c:6621
> >> schedule_preempt_disabled+0x13/0x30 kernel/sched/core.c:6678
> >> __mutex_lock_common kernel/locking/mutex.c:684 [inline]
> >> __mutex_lock+0x6a4/0xd70 kernel/locking/mutex.c:752
> >> register_nexthop_notifier+0x84/0x290 net/ipv4/nexthop.c:3871
> >> ops_init+0x359/0x610 net/core/net_namespace.c:139
> >> setup_net+0x515/0xca0 net/core/net_namespace.c:343
> >> copy_net_ns+0x4e2/0x7b0 net/core/net_namespace.c:508
> >> create_new_namespaces+0x425/0x7b0 kernel/nsproxy.c:110
> >> unshare_nsproxy_namespaces+0x124/0x180 kernel/nsproxy.c:228
> >> ksys_unshare+0x619/0xc10 kernel/fork.c:3308
> >> __do_sys_unshare kernel/fork.c:3379 [inline]
> >> __se_sys_unshare kernel/fork.c:3377 [inline]
> >> __x64_sys_unshare+0x38/0x40 kernel/fork.c:3377
> >> do_syscall_x64 arch/x86/entry/common.c:52 [inline]
> >> do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
> >> entry_SYSCALL_64_after_hwframe+0x77/0x7f
> >> RIP: 0033:0x7f61f45772b7
> >> RSP: 002b:00007f61f482ffa8 EFLAGS: 00000206 ORIG_RAX: 0000000000000110
> >> RAX: ffffffffffffffda RBX: 00007f61f45e4bd1 RCX: 00007f61f45772b7
> >> RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000040000000
> >> RBP: 0000000000000000 R08: 00007f61f5237d60 R09: 0000000000000000
> >> R10: 0000000000000000 R11: 0000000000000206 R12: 000000000000000c
> >> R13: 0000000000000003 R14: 0000000000000009 R15: 0000000000000009
> >> </TASK>
> >> INFO: task syz-executor:5432 blocked for more than 152 seconds.
> >> Not tainted 6.10.0-syzkaller-08280-g68b59730459e #0
> >> "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> >> task:syz-executor state:D
> >> stack:25712 pid:5432 tgid:5432 ppid:1 flags:0x00004006
> >> Call Trace:
> >> <TASK>
> >> context_switch kernel/sched/core.c:5188 [inline]
> >> __schedule+0x1800/0x4a60 kernel/sched/core.c:6529
> >> __schedule_loop kernel/sched/core.c:6606 [inline]
> >> schedule+0x14b/0x320 kernel/sched/core.c:6621
> >> schedule_preempt_disabled+0x13/0x30 kernel/sched/core.c:6678
> >> __mutex_lock_common kernel/locking/mutex.c:684 [inline]
> >> __mutex_lock+0x6a4/0xd70 kernel/locking/mutex.c:752
> >> register_nexthop_notifier+0x84/0x290 net/ipv4/nexthop.c:3871
> >> ops_init+0x359/0x610 net/core/net_namespace.c:139
> >> setup_net+0x515/0xca0 net/core/net_namespace.c:343
> >> copy_net_ns+0x4e2/0x7b0 net/core/net_namespace.c:508
> >> create_new_namespaces+0x425/0x7b0 kernel/nsproxy.c:110
> >> unshare_nsproxy_namespaces+0x124/0x180 kernel/nsproxy.c:228
> >> ksys_unshare+0x619/0xc10 kernel/fork.c:3308
> >>
> >>
> >> ---
> >> 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@xxxxxxxxxxxxxxxx.
> >>
> >> syzbot will keep track of this issue. See:
> >> https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
> >>
> >> If the report is already addressed, let syzbot know by replying with:
> >> #syz fix: exact-commit-title
> >>
> >> If you want to overwrite report's subsystems, reply with:
> >> #syz set subsystems: new-subsystem
> >> (See the list of subsystem names on the web dashboard)
> >>
> >> If the report is a duplicate of another one, reply with:
> >> #syz dup: exact-subject-of-another-report
> >>
> >> If you want to undo deduplication, reply with:
> >> #syz undup
> >
> > The fact that netdevsim uses a sysfs file to add/delete netdevice
> > seems unfortunate,
> > because of the classical sysfs vs rtnl issue (see rtnl_trylock() calls
> > in net/core/net-sysfs.c for reference)
>
> Hi Eric, what is the classical sysfs vs rtnl issue? Is it a race,
> AA/ABBA deadlock, or just slowness due to contention on rtnl_mutex?

I have seen many "task hung" syzbot reports with netdevsim being involved...

Perhaps the following path should be done from a different context ( a
work queue )

context_switch kernel/sched/core.c:5188 [inline]
__schedule+0x1800/0x4a60 kernel/sched/core.c:6529
__schedule_loop kernel/sched/core.c:6606 [inline]
schedule+0x14b/0x320 kernel/sched/core.c:6621
schedule_preempt_disabled+0x13/0x30 kernel/sched/core.c:6678
__mutex_lock_common kernel/locking/mutex.c:684 [inline]
__mutex_lock+0x6a4/0xd70 kernel/locking/mutex.c:752
nsim_destroy+0x71/0x5c0 drivers/net/netdevsim/netdev.c:773
__nsim_dev_port_del+0x14b/0x1b0 drivers/net/netdevsim/dev.c:1425
nsim_dev_port_del_all drivers/net/netdevsim/dev.c:1437 [inline]
nsim_dev_reload_destroy+0x28a/0x490 drivers/net/netdevsim/dev.c:1658
nsim_drv_remove+0x58/0x160 drivers/net/netdevsim/dev.c:1673
device_remove drivers/base/dd.c:566 [inline]
__device_release_driver drivers/base/dd.c:1270 [inline]
device_release_driver_internal+0x4a9/0x7c0 drivers/base/dd.c:1293
bus_remove_device+0x34f/0x420 drivers/base/bus.c:574
device_del+0x57a/0x9b0 drivers/base/core.c:3868
device_unregister+0x20/0xc0 drivers/base/core.c:3909
nsim_bus_dev_del drivers/net/netdevsim/bus.c:462 [inline]
del_device_store+0x363/0x480 drivers/net/netdevsim/bus.c:226
kernfs_fop_write_iter+0x3a1/0x500 fs/kernfs/file.c:334
// of->mutex held here
new_sync_write fs/read_write.c:497 [inline]
vfs_write+0xa72/0xc90 fs/read_write.c:590

>
> This thread [1] says it is a deadlock.
>
> I found this commit 5a5990d3 net: Avoid race between network down and
> sysfs, but the description doesn't go into detail what exactly the race
> is.
>
> Would using Netlink API for doing netdevsim operations solve the issue?
>
> [1]: https://lore.kernel.org/netdev/20231018154804.420823-1-atenart@xxxxxxxxxx/

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