[syzbot] [net?] unregister_netdevice: waiting for DEV to become free (8)

[syzbot] [net?] unregister_netdevice: waiting for DEV to become free (8)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    67faabbde36b selftests/bpf: Add missing prototypes for sev..
git tree:       bpf-next
console+strace: https://syzkaller.appspot.com/x/log.txt?x=1381363b280000
kernel config:  https://syzkaller.appspot.com/x/.config?x=5335204dcdecfda
dashboard link: https://syzkaller.appspot.com/bug?extid=881d65229ca4f9ae8c84
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=132faf93280000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=10532add280000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/751a0490d875/disk-67faabbd.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/2c5106cd9f1f/vmlinux-67faabbd.xz
kernel image: https://storage.googleapis.com/syzbot-assets/62c1154294e4/bzImage-67faabbd.xz

The issue was bisected to:

commit ad2f99aedf8fa77f3ae647153284fa63c43d3055
Author: Arnd Bergmann <arnd@arndb.de>
Date:   Tue Jul 27 13:45:16 2021 +0000

    net: bridge: move bridge ioctls out of .ndo_do_ioctl

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=146de6f1280000
final oops:     https://syzkaller.appspot.com/x/report.txt?x=166de6f1280000
console output: https://syzkaller.appspot.com/x/log.txt?x=126de6f1280000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+881d65229ca4f9ae8c84@syzkaller.appspotmail.com
Fixes: ad2f99aedf8f ("net: bridge: move bridge ioctls out of .ndo_do_ioctl")

unregister_netdevice: waiting for bridge0 to become free. Usage count = 2
leaked reference.
 __netdev_tracker_alloc include/linux/netdevice.h:4070 [inline]
 netdev_hold include/linux/netdevice.h:4099 [inline]
 dev_ifsioc+0xbc0/0xeb0 net/core/dev_ioctl.c:408
 dev_ioctl+0x250/0x1090 net/core/dev_ioctl.c:605
 sock_do_ioctl+0x15a/0x230 net/socket.c:1215
 sock_ioctl+0x1f8/0x680 net/socket.c:1318
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:870 [inline]
 __se_sys_ioctl fs/ioctl.c:856 [inline]
 __x64_sys_ioctl+0x197/0x210 fs/ioctl.c:856
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x39/0xb0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd


---
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

If the bug is already fixed, let syzbot know by replying with:
#syz fix: exact-commit-title

If you want syzbot to run the reproducer, reply with:
#syz test: git://repo/address.git branch-or-commit-hash
If you attach or paste a git patch, syzbot will apply it before testing.

If you want to change bug's subsystems, reply with:
#syz set subsystems: new-subsystem
(See the list of subsystem names on the web dashboard)

If the bug is a duplicate of another bug, reply with:
#syz dup: exact-subject-of-another-report

If you want to undo deduplication, reply with:
#syz undup

Re: [syzbot] [net?] unregister_netdevice: waiting for DEV to become free (8)

[Dongliang Mu]

On Wed, Jun 21, 2023 at 3:38 PM 'Ziqi Zhao' via syzkaller-bugs
<syzkaller-bugs@googlegroups.com> wrote:
>
> Hi all,
>
> I'm taking a look at this bug as part of the exercice for the Linux
> Kernel Bug Fixing Summer 2023 program. Thanks to the help from my

This is an interesting program. There are many kernel crashes on the
syzbot dashboard, which needs help.

> mentor, Ivan Orlov and Shuah Khan, I've already obtained a reproduction
> of the issue using the provided C reproducer, and I should be able to
> submit a patch by the end of this week to fix the highlighted error. If
> you have any information or suggestions, please feel free to reply to
> this thread. Any help would be greatly appreciated!

Please carefully read the guidance of submitting patches to linux
kernel [1]. Be careful about your coding style before sending.

Note that, Syzbot has the feature: patch testing. You can upload and
test your own patch to confirm that your patch is working properly.

[1] https://docs.kernel.org/process/submitting-patches.html
>
> Best regards,
> Ziqi
>
> --
> You received this message because you are subscribed to the Google Groups "syzkaller-bugs" group.
> To unsubscribe from this group and stop receiving emails from it, send an email to syzkaller-bugs+unsubscribe@googlegroups.com.
> To view this discussion on the web visit https://groups.google.com/d/msgid/syzkaller-bugs/20230621070710.380373-1-astrajoan%40yahoo.com.

Re: [syzbot] [net?] unregister_netdevice: waiting for DEV to become free (8)

[Hillf Danton]

> Date: Fri, 09 Jun 2023 18:34:58 -0700	[thread overview]
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    67faabbde36b selftests/bpf: Add missing prototypes for sev..
> git tree:       bpf-next
> console+strace: https://syzkaller.appspot.com/x/log.txt?x=1381363b280000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=5335204dcdecfda
> dashboard link: https://syzkaller.appspot.com/bug?extid=881d65229ca4f9ae8c84
> 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=132faf93280000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=10532add280000

#syz test upstream master

--- a/net/can/j1939/j1939-priv.h
+++ b/net/can/j1939/j1939-priv.h
@@ -59,6 +59,7 @@ struct j1939_priv {
 	/* segments need a lock to protect the above list */
 	rwlock_t lock;
 
+	int unregistered;
 	struct net_device *ndev;
 
 	/* list of 256 ecu ptrs, that cache the claimed addresses.
--- a/net/can/j1939/main.c
+++ b/net/can/j1939/main.c
@@ -157,13 +157,15 @@ static void __j1939_priv_release(struct
 	struct j1939_priv *priv = container_of(kref, struct j1939_priv, kref);
 	struct net_device *ndev = priv->ndev;
 
-	netdev_dbg(priv->ndev, "%s: 0x%p\n", __func__, priv);
+	if (!priv->unregistered)
+		netdev_dbg(priv->ndev, "%s: 0x%p\n", __func__, priv);
 
 	WARN_ON_ONCE(!list_empty(&priv->active_session_list));
 	WARN_ON_ONCE(!list_empty(&priv->ecus));
 	WARN_ON_ONCE(!list_empty(&priv->j1939_socks));
 
-	dev_put(ndev);
+	if (!priv->unregistered)
+		dev_put(ndev);
 	kfree(priv);
 }
 
@@ -377,6 +379,10 @@ static int j1939_netdev_notify(struct no
 		j1939_sk_netdev_event_netdown(priv);
 		j1939_ecu_unmap_all(priv);
 		break;
+	case NETDEV_UNREGISTER:
+		priv->unregistered++;
+		dev_put(priv->ndev);
+		break;
 	}
 
 	j1939_priv_put(priv);
--

Re: [syzbot] [net?] unregister_netdevice: waiting for DEV to become free (8)

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger any issue:

Reported-by: syzbot+881d65229ca4f9ae8c84@syzkaller.appspotmail.com
Tested-by: syzbot+881d65229ca4f9ae8c84@syzkaller.appspotmail.com

Tested on:

commit:         1b237f19 Linux 6.17-rc3
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=144dec42580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=d4703ac89d9e185a
dashboard link: https://syzkaller.appspot.com/bug?extid=881d65229ca4f9ae8c84
compiler:       gcc (Debian 12.2.0-14+deb12u1) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
patch:          https://syzkaller.appspot.com/x/patch.diff?x=10cefa34580000

Note: testing is done by a robot and is best-effort only.

Re: [syzbot] [net?] unregister_netdevice: waiting for DEV to become free (8)

[syzbot]

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
KASAN: use-after-free Read in j1939_netdev_stop

==================================================================
BUG: KASAN: use-after-free in read_pnet include/net/net_namespace.h:409 [inline]
BUG: KASAN: use-after-free in dev_net include/linux/netdevice.h:2718 [inline]
BUG: KASAN: use-after-free in j1939_can_rx_unregister net/can/j1939/main.c:202 [inline]
BUG: KASAN: use-after-free in __j1939_rx_release net/can/j1939/main.c:218 [inline]
BUG: KASAN: use-after-free in kref_put_mutex include/linux/kref.h:86 [inline]
BUG: KASAN: use-after-free in j1939_netdev_stop+0x2ab/0x2d0 net/can/j1939/main.c:311
Read of size 8 at addr ffff888023f80108 by task syz.0.17/6524

CPU: 0 UID: 0 PID: 6524 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x116/0x1f0 lib/dump_stack.c:120
 print_address_description mm/kasan/report.c:378 [inline]
 print_report+0xcd/0x630 mm/kasan/report.c:482
 kasan_report+0xe0/0x110 mm/kasan/report.c:595
 read_pnet include/net/net_namespace.h:409 [inline]
 dev_net include/linux/netdevice.h:2718 [inline]
 j1939_can_rx_unregister net/can/j1939/main.c:202 [inline]
 __j1939_rx_release net/can/j1939/main.c:218 [inline]
 kref_put_mutex include/linux/kref.h:86 [inline]
 j1939_netdev_stop+0x2ab/0x2d0 net/can/j1939/main.c:311
 j1939_sk_release+0x5c3/0x8e0 net/can/j1939/socket.c:651
 __sock_release+0xb3/0x270 net/socket.c:649
 sock_close+0x1c/0x30 net/socket.c:1439
 __fput+0x402/0xb70 fs/file_table.c:468
 task_work_run+0x14d/0x240 kernel/task_work.c:227
 exit_task_work include/linux/task_work.h:40 [inline]
 do_exit+0x86f/0x2bf0 kernel/exit.c:961
 do_group_exit+0xd3/0x2a0 kernel/exit.c:1102
 get_signal+0x2673/0x26d0 kernel/signal.c:3034
 arch_do_signal_or_restart+0x8f/0x7d0 arch/x86/kernel/signal.c:337
 exit_to_user_mode_loop+0x84/0x110 kernel/entry/common.c:40
 exit_to_user_mode_prepare include/linux/irq-entry-common.h:225 [inline]
 syscall_exit_to_user_mode_work include/linux/entry-common.h:175 [inline]
 syscall_exit_to_user_mode include/linux/entry-common.h:210 [inline]
 do_syscall_64+0x3f6/0x4c0 arch/x86/entry/syscall_64.c:100
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f408338ebe9
Code: Unable to access opcode bytes at 0x7f408338ebbf.
RSP: 002b:00007f4084235038 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: 0000000000000024 RBX: 00007f40835b5fa0 RCX: 00007f408338ebe9
RDX: 0000000000000000 RSI: 0000200000000200 RDI: 0000000000000003
RBP: 00007f4083411e19 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f40835b6038 R14: 00007f40835b5fa0 R15: 00007ffd085a2ed8
 </TASK>

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0xffff888023f80000 pfn:0x23f80
flags: 0xfff00000000000(node=0|zone=1|lastcpupid=0x7ff)
raw: 00fff00000000000 ffffea000174f608 ffffea0000c2c208 0000000000000000
raw: ffff888023f80000 0000000000000000 00000000ffffffff 0000000000000000
page dumped because: kasan: bad access detected
page_owner tracks the page as freed
page last allocated via order 3, migratetype Unmovable, gfp_mask 0x446dc0(GFP_KERNEL_ACCOUNT|__GFP_ZERO|__GFP_NOWARN|__GFP_RETRY_MAYFAIL|__GFP_COMP), pid 6440, tgid 6440 (syz-executor), ts 122667010586, free_ts 125938931446
 set_page_owner include/linux/page_owner.h:32 [inline]
 post_alloc_hook+0x1c0/0x230 mm/page_alloc.c:1851
 prep_new_page mm/page_alloc.c:1859 [inline]
 get_page_from_freelist+0x132b/0x38e0 mm/page_alloc.c:3858
 __alloc_frozen_pages_noprof+0x261/0x23f0 mm/page_alloc.c:5148
 alloc_pages_mpol+0x1fb/0x550 mm/mempolicy.c:2416
 ___kmalloc_large_node+0xed/0x160 mm/slub.c:4306
 __kmalloc_large_node_noprof+0x1c/0x70 mm/slub.c:4337
 __do_kmalloc_node mm/slub.c:4353 [inline]
 __kvmalloc_node_noprof.cold+0xb/0x65 mm/slub.c:5052
 alloc_netdev_mqs+0xd2/0x1530 net/core/dev.c:11812
 rtnl_create_link+0xc08/0xf90 net/core/rtnetlink.c:3633
 vxcan_newlink+0x2f8/0x640 drivers/net/can/vxcan.c:208
 rtnl_newlink_create net/core/rtnetlink.c:3825 [inline]
 __rtnl_newlink net/core/rtnetlink.c:3942 [inline]
 rtnl_newlink+0xc45/0x2000 net/core/rtnetlink.c:4057
 rtnetlink_rcv_msg+0x95e/0xe90 net/core/rtnetlink.c:6946
 netlink_rcv_skb+0x158/0x420 net/netlink/af_netlink.c:2552
 netlink_unicast_kernel net/netlink/af_netlink.c:1320 [inline]
 netlink_unicast+0x5a7/0x870 net/netlink/af_netlink.c:1346
 netlink_sendmsg+0x8d1/0xdd0 net/netlink/af_netlink.c:1896
 sock_sendmsg_nosec net/socket.c:714 [inline]
 __sock_sendmsg net/socket.c:729 [inline]
 __sys_sendto+0x4a3/0x520 net/socket.c:2228
page last free pid 6524 tgid 6523 stack trace:
 reset_page_owner include/linux/page_owner.h:25 [inline]
 free_pages_prepare mm/page_alloc.c:1395 [inline]
 __free_frozen_pages+0x7d5/0x10f0 mm/page_alloc.c:2895
 device_release+0xa1/0x240 drivers/base/core.c:2565
 kobject_cleanup lib/kobject.c:689 [inline]
 kobject_release lib/kobject.c:720 [inline]
 kref_put include/linux/kref.h:65 [inline]
 kobject_put+0x1e7/0x5a0 lib/kobject.c:737
 netdev_run_todo+0x7e9/0x1320 net/core/dev.c:11513
 rtnl_unlock net/core/rtnetlink.c:157 [inline]
 rtnl_net_unlock include/linux/rtnetlink.h:135 [inline]
 rtnl_dellink+0x3da/0xa80 net/core/rtnetlink.c:3563
 rtnetlink_rcv_msg+0x95e/0xe90 net/core/rtnetlink.c:6946
 netlink_rcv_skb+0x158/0x420 net/netlink/af_netlink.c:2552
 netlink_unicast_kernel net/netlink/af_netlink.c:1320 [inline]
 netlink_unicast+0x5a7/0x870 net/netlink/af_netlink.c:1346
 netlink_sendmsg+0x8d1/0xdd0 net/netlink/af_netlink.c:1896
 sock_sendmsg_nosec net/socket.c:714 [inline]
 __sock_sendmsg net/socket.c:729 [inline]
 ____sys_sendmsg+0xa95/0xc70 net/socket.c:2614
 ___sys_sendmsg+0x134/0x1d0 net/socket.c:2668
 __sys_sendmsg+0x16d/0x220 net/socket.c:2700
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xcd/0x4c0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Memory state around the buggy address:
 ffff888023f80000: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff888023f80080: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>ffff888023f80100: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                      ^
 ffff888023f80180: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff888023f80200: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
==================================================================


Tested on:

commit:         1b237f19 Linux 6.17-rc3
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=10b66862580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=d4703ac89d9e185a
dashboard link: https://syzkaller.appspot.com/bug?extid=881d65229ca4f9ae8c84
compiler:       gcc (Debian 12.2.0-14+deb12u1) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
patch:          https://syzkaller.appspot.com/x/patch.diff?x=1417b862580000

Re: [syzbot] [net?] unregister_netdevice: waiting for DEV to become free (8)

[Hillf Danton]

> Date: Fri, 09 Jun 2023 18:34:58 -0700	[thread overview]
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    67faabbde36b selftests/bpf: Add missing prototypes for sev..
> git tree:       bpf-next
> console+strace: https://syzkaller.appspot.com/x/log.txt?x=1381363b280000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=5335204dcdecfda
> dashboard link: https://syzkaller.appspot.com/bug?extid=881d65229ca4f9ae8c84
> 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=132faf93280000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=10532add280000

#syz test upstream master

--- a/net/can/j1939/j1939-priv.h
+++ b/net/can/j1939/j1939-priv.h
@@ -59,6 +59,7 @@ struct j1939_priv {
 	/* segments need a lock to protect the above list */
 	rwlock_t lock;
 
+	int unregistered;
 	struct net_device *ndev;
 
 	/* list of 256 ecu ptrs, that cache the claimed addresses.
--- a/net/can/j1939/main.c
+++ b/net/can/j1939/main.c
@@ -157,13 +157,15 @@ static void __j1939_priv_release(struct
 	struct j1939_priv *priv = container_of(kref, struct j1939_priv, kref);
 	struct net_device *ndev = priv->ndev;
 
-	netdev_dbg(priv->ndev, "%s: 0x%p\n", __func__, priv);
+	if (!priv->unregistered)
+		netdev_dbg(priv->ndev, "%s: 0x%p\n", __func__, priv);
 
 	WARN_ON_ONCE(!list_empty(&priv->active_session_list));
 	WARN_ON_ONCE(!list_empty(&priv->ecus));
 	WARN_ON_ONCE(!list_empty(&priv->j1939_socks));
 
-	dev_put(ndev);
+	if (!priv->unregistered)
+		dev_put(ndev);
 	kfree(priv);
 }
 
@@ -197,7 +199,8 @@ static void j1939_can_rx_unregister(stru
 {
 	struct net_device *ndev = priv->ndev;
 
-	can_rx_unregister(dev_net(ndev), ndev, J1939_CAN_ID, J1939_CAN_MASK,
+	if (!priv->unregistered)
+		can_rx_unregister(dev_net(ndev), ndev, J1939_CAN_ID, J1939_CAN_MASK,
 			  j1939_can_recv, priv);
 
 	/* The last reference of priv is dropped by the RCU deferred
@@ -377,6 +380,10 @@ static int j1939_netdev_notify(struct no
 		j1939_sk_netdev_event_netdown(priv);
 		j1939_ecu_unmap_all(priv);
 		break;
+	case NETDEV_UNREGISTER:
+		priv->unregistered++;
+		dev_put(priv->ndev);
+		break;
 	}
 
 	j1939_priv_put(priv);
--

Re: [syzbot] [net?] unregister_netdevice: waiting for DEV to become free (8)

[syzbot]

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
KASAN: use-after-free Read in j1939_netdev_stop

==================================================================
BUG: KASAN: use-after-free in netdev_get_ml_priv include/linux/netdevice.h:2692 [inline]
BUG: KASAN: use-after-free in can_get_ml_priv include/linux/can/can-ml.h:71 [inline]
BUG: KASAN: use-after-free in j1939_priv_set net/can/j1939/main.c:150 [inline]
BUG: KASAN: use-after-free in __j1939_rx_release net/can/j1939/main.c:221 [inline]
BUG: KASAN: use-after-free in kref_put_mutex include/linux/kref.h:86 [inline]
BUG: KASAN: use-after-free in j1939_netdev_stop+0x2df/0x320 net/can/j1939/main.c:312
Read of size 4 at addr ffff888062a506b0 by task syz.0.17/6467

CPU: 0 UID: 0 PID: 6467 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x116/0x1f0 lib/dump_stack.c:120
 print_address_description mm/kasan/report.c:378 [inline]
 print_report+0xcd/0x630 mm/kasan/report.c:482
 kasan_report+0xe0/0x110 mm/kasan/report.c:595
 netdev_get_ml_priv include/linux/netdevice.h:2692 [inline]
 can_get_ml_priv include/linux/can/can-ml.h:71 [inline]
 j1939_priv_set net/can/j1939/main.c:150 [inline]
 __j1939_rx_release net/can/j1939/main.c:221 [inline]
 kref_put_mutex include/linux/kref.h:86 [inline]
 j1939_netdev_stop+0x2df/0x320 net/can/j1939/main.c:312
 j1939_sk_release+0x5c3/0x8e0 net/can/j1939/socket.c:651
 __sock_release+0xb0/0x270 net/socket.c:649
 sock_close+0x1c/0x30 net/socket.c:1439
 __fput+0x402/0xb70 fs/file_table.c:468
 task_work_run+0x14d/0x240 kernel/task_work.c:227
 exit_task_work include/linux/task_work.h:40 [inline]
 do_exit+0x86f/0x2bf0 kernel/exit.c:961
 do_group_exit+0xd3/0x2a0 kernel/exit.c:1102
 get_signal+0x2673/0x26d0 kernel/signal.c:3034
 arch_do_signal_or_restart+0x8f/0x7d0 arch/x86/kernel/signal.c:337
 exit_to_user_mode_loop+0x84/0x110 kernel/entry/common.c:40
 exit_to_user_mode_prepare include/linux/irq-entry-common.h:225 [inline]
 syscall_exit_to_user_mode_work include/linux/entry-common.h:175 [inline]
 syscall_exit_to_user_mode include/linux/entry-common.h:210 [inline]
 do_syscall_64+0x3f6/0x4c0 arch/x86/entry/syscall_64.c:100
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f15b7b8ebe9
Code: Unable to access opcode bytes at 0x7f15b7b8ebbf.
RSP: 002b:00007f15b899d038 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: 0000000000000024 RBX: 00007f15b7db5fa0 RCX: 00007f15b7b8ebe9
RDX: 0000000000000000 RSI: 0000200000000200 RDI: 0000000000000003
RBP: 00007f15b7c11e19 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f15b7db6038 R14: 00007f15b7db5fa0 R15: 00007ffec48e9178
 </TASK>

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x62a50
flags: 0xfff00000000000(node=0|zone=1|lastcpupid=0x7ff)
raw: 00fff00000000000 ffffea0001db7008 ffffea00018a9208 0000000000000000
raw: 0000000000000000 0000000000000000 00000000ffffffff 0000000000000000
page dumped because: kasan: bad access detected
page_owner tracks the page as freed
page last allocated via order 3, migratetype Unmovable, gfp_mask 0x446dc0(GFP_KERNEL_ACCOUNT|__GFP_ZERO|__GFP_NOWARN|__GFP_RETRY_MAYFAIL|__GFP_COMP), pid 6357, tgid 6357 (syz-executor), ts 118494889601, free_ts 123112554125
 set_page_owner include/linux/page_owner.h:32 [inline]
 post_alloc_hook+0x1c0/0x230 mm/page_alloc.c:1851
 prep_new_page mm/page_alloc.c:1859 [inline]
 get_page_from_freelist+0x132b/0x38e0 mm/page_alloc.c:3858
 __alloc_frozen_pages_noprof+0x261/0x23f0 mm/page_alloc.c:5148
 alloc_pages_mpol+0x1fb/0x550 mm/mempolicy.c:2416
 ___kmalloc_large_node+0xed/0x160 mm/slub.c:4306
 __kmalloc_large_node_noprof+0x1c/0x70 mm/slub.c:4337
 __do_kmalloc_node mm/slub.c:4353 [inline]
 __kvmalloc_node_noprof.cold+0xb/0x65 mm/slub.c:5052
 alloc_netdev_mqs+0xd2/0x1530 net/core/dev.c:11812
 rtnl_create_link+0xc08/0xf90 net/core/rtnetlink.c:3633
 vxcan_newlink+0x2f8/0x640 drivers/net/can/vxcan.c:208
 rtnl_newlink_create net/core/rtnetlink.c:3825 [inline]
 __rtnl_newlink net/core/rtnetlink.c:3942 [inline]
 rtnl_newlink+0xc45/0x2000 net/core/rtnetlink.c:4057
 rtnetlink_rcv_msg+0x95b/0xe90 net/core/rtnetlink.c:6946
 netlink_rcv_skb+0x155/0x420 net/netlink/af_netlink.c:2552
 netlink_unicast_kernel net/netlink/af_netlink.c:1320 [inline]
 netlink_unicast+0x5aa/0x870 net/netlink/af_netlink.c:1346
 netlink_sendmsg+0x8d1/0xdd0 net/netlink/af_netlink.c:1896
 sock_sendmsg_nosec net/socket.c:714 [inline]
 __sock_sendmsg net/socket.c:729 [inline]
 __sys_sendto+0x4a0/0x520 net/socket.c:2228
page last free pid 6467 tgid 6466 stack trace:
 reset_page_owner include/linux/page_owner.h:25 [inline]
 free_pages_prepare mm/page_alloc.c:1395 [inline]
 __free_frozen_pages+0x7d5/0x10f0 mm/page_alloc.c:2895
 device_release+0xa1/0x240 drivers/base/core.c:2565
 kobject_cleanup lib/kobject.c:689 [inline]
 kobject_release lib/kobject.c:720 [inline]
 kref_put include/linux/kref.h:65 [inline]
 kobject_put+0x1e7/0x5a0 lib/kobject.c:737
 netdev_run_todo+0x7e9/0x1320 net/core/dev.c:11513
 rtnl_unlock net/core/rtnetlink.c:157 [inline]
 rtnl_net_unlock include/linux/rtnetlink.h:135 [inline]
 rtnl_dellink+0x3da/0xa80 net/core/rtnetlink.c:3563
 rtnetlink_rcv_msg+0x95b/0xe90 net/core/rtnetlink.c:6946
 netlink_rcv_skb+0x155/0x420 net/netlink/af_netlink.c:2552
 netlink_unicast_kernel net/netlink/af_netlink.c:1320 [inline]
 netlink_unicast+0x5aa/0x870 net/netlink/af_netlink.c:1346
 netlink_sendmsg+0x8d1/0xdd0 net/netlink/af_netlink.c:1896
 sock_sendmsg_nosec net/socket.c:714 [inline]
 __sock_sendmsg net/socket.c:729 [inline]
 ____sys_sendmsg+0xa98/0xc70 net/socket.c:2614
 ___sys_sendmsg+0x134/0x1d0 net/socket.c:2668
 __sys_sendmsg+0x16d/0x220 net/socket.c:2700
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xcd/0x4c0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Memory state around the buggy address:
 ffff888062a50580: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff888062a50600: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>ffff888062a50680: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                                     ^
 ffff888062a50700: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff888062a50780: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
==================================================================


Tested on:

commit:         fab1beda Merge tag 'devicetree-fixes-for-6.17-1' of gi..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=16049c42580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=d4703ac89d9e185a
dashboard link: https://syzkaller.appspot.com/bug?extid=881d65229ca4f9ae8c84
compiler:       gcc (Debian 12.2.0-14+deb12u1) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
patch:          https://syzkaller.appspot.com/x/patch.diff?x=142de862580000

unregister_netdevice: waiting for DEV to become free (8)

[Tetsuo Handa]

Let me check whether a reproducer that can still reproduce this problem is used for testing.

#syz test: git://git.code.sf.net/p/tomoyo/tomoyo.git

Re: unregister_netdevice: waiting for DEV to become free (8)

[syzbot]

> Let me check whether a reproducer that can still reproduce this problem is used for testing.
>
> #syz test: git://git.code.sf.net/p/tomoyo/tomoyo.git

I've failed to parse your command.
Did you perhaps forget to provide the branch name, or added an extra ':'?
Please use one of the two supported formats:
1. #syz test
2. #syz test: repo branch-or-commit-hash
Note the lack of ':' in option 1.

Re: unregister_netdevice: waiting for DEV to become free (8)

[Tetsuo Handa]

#syz test: git://git.code.sf.net/p/tomoyo/tomoyo.git master

Re: [syzbot] [net?] unregister_netdevice: waiting for DEV to become free (8)

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger any issue:

Reported-by: syzbot+881d65229ca4f9ae8c84@syzkaller.appspotmail.com
Tested-by: syzbot+881d65229ca4f9ae8c84@syzkaller.appspotmail.com

Tested on:

commit:         5ac798f7 net/can/j1939: add j1939_priv debugging
git tree:       git://git.code.sf.net/p/tomoyo/tomoyo.git master
console output: https://syzkaller.appspot.com/x/log.txt?x=10a5a8b4580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=7fd2b6b29c6ab719
dashboard link: https://syzkaller.appspot.com/bug?extid=881d65229ca4f9ae8c84
compiler:       Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8

Note: no patches were applied.
Note: testing is done by a robot and is best-effort only.

Re: unregister_netdevice: waiting for DEV to become free (8)

[Tetsuo Handa]

Trying once more.

#syz test: git://git.code.sf.net/p/tomoyo/tomoyo.git master

Re: [syzbot] [net?] unregister_netdevice: waiting for DEV to become free (8)

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger any issue:

Reported-by: syzbot+881d65229ca4f9ae8c84@syzkaller.appspotmail.com
Tested-by: syzbot+881d65229ca4f9ae8c84@syzkaller.appspotmail.com

Tested on:

commit:         5ac798f7 net/can/j1939: add j1939_priv debugging
git tree:       git://git.code.sf.net/p/tomoyo/tomoyo.git master
console output: https://syzkaller.appspot.com/x/log.txt?x=17b5a8b4580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=7fd2b6b29c6ab719
dashboard link: https://syzkaller.appspot.com/bug?extid=881d65229ca4f9ae8c84
compiler:       Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8

Note: no patches were applied.
Note: testing is done by a robot and is best-effort only.

Re: unregister_netdevice: waiting for DEV to become free (8)

[Tetsuo Handa]

Too timing-dependent to trigger using a reproducer?
Or, a reproducer for an already-fixed bug is used?

#syz test
diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index d1a687444b27..798d60b3e2ad 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -2084,6 +2084,8 @@ enum netdev_reg_state {
  *
  *	FIXME: cleanup struct net_device such that network protocol info
  *	moves out.
+ *
+ *	@netdev_trace_buffer_list: Linked list for debugging refcount leak.
  */
 
 struct net_device {
@@ -2238,6 +2240,9 @@ struct net_device {
 #if IS_ENABLED(CONFIG_TLS_DEVICE)
 	const struct tlsdev_ops *tlsdev_ops;
 #endif
+#ifdef CONFIG_NET_DEV_REFCNT_TRACKER
+	struct list_head	netdev_trace_buffer_list;
+#endif
 
 	unsigned int		operstate;
 	unsigned char		link_mode;
@@ -3166,6 +3171,7 @@ enum netdev_cmd {
 	NETDEV_OFFLOAD_XSTATS_REPORT_USED,
 	NETDEV_OFFLOAD_XSTATS_REPORT_DELTA,
 	NETDEV_XDP_FEAT_CHANGE,
+	NETDEV_DEBUG_UNREGISTER,
 };
 const char *netdev_cmd_to_name(enum netdev_cmd cmd);
 
@@ -4345,9 +4351,15 @@ static inline bool dev_nit_active(const struct net_device *dev)
 
 void dev_queue_xmit_nit(struct sk_buff *skb, struct net_device *dev);
 
+void save_netdev_trace_buffer(struct net_device *dev, int delta);
+int trim_netdev_trace(unsigned long *entries, int nr_entries);
+
 static inline void __dev_put(struct net_device *dev)
 {
 	if (dev) {
+#ifdef CONFIG_NET_DEV_REFCNT_TRACKER
+		save_netdev_trace_buffer(dev, -1);
+#endif
 #ifdef CONFIG_PCPU_DEV_REFCNT
 		this_cpu_dec(*dev->pcpu_refcnt);
 #else
@@ -4359,6 +4371,9 @@ static inline void __dev_put(struct net_device *dev)
 static inline void __dev_hold(struct net_device *dev)
 {
 	if (dev) {
+#ifdef CONFIG_NET_DEV_REFCNT_TRACKER
+		save_netdev_trace_buffer(dev, 1);
+#endif
 #ifdef CONFIG_PCPU_DEV_REFCNT
 		this_cpu_inc(*dev->pcpu_refcnt);
 #else
diff --git a/kernel/softirq.c b/kernel/softirq.c
index 77198911b8dd..5f435c1e48d8 100644
--- a/kernel/softirq.c
+++ b/kernel/softirq.c
@@ -576,6 +576,10 @@ static inline bool lockdep_softirq_start(void) { return false; }
 static inline void lockdep_softirq_end(bool in_hardirq) { }
 #endif
 
+#ifdef CONFIG_NET_DEV_REFCNT_TRACKER
+static noinline void handle_softirqs(bool ksirqd);
+#endif
+
 static void handle_softirqs(bool ksirqd)
 {
 	unsigned long end = jiffies + MAX_SOFTIRQ_TIME;
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 45320e27a16c..e9c654a9d0bb 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -3145,6 +3145,10 @@ static bool manage_workers(struct worker *worker)
 	return true;
 }
 
+#ifdef CONFIG_NET_DEV_REFCNT_TRACKER
+static noinline void process_one_work(struct worker *worker, struct work_struct *work);
+#endif
+
 /**
  * process_one_work - process single work
  * @worker: self
diff --git a/net/can/j1939/main.c b/net/can/j1939/main.c
index a93af55df5fd..66e6624abfa3 100644
--- a/net/can/j1939/main.c
+++ b/net/can/j1939/main.c
@@ -124,6 +124,16 @@ static void j1939_can_recv(struct sk_buff *iskb, void *data)
 
 static DEFINE_MUTEX(j1939_netdev_lock);
 
+#ifdef CONFIG_NET_DEV_REFCNT_TRACKER
+static void dump_priv_trace_buffer(const struct net_device *ndev);
+static void erase_priv_trace_buffer(struct j1939_priv *priv);
+static noinline void save_priv_trace_buffer(struct j1939_priv *priv, int delta);
+#else
+static inline void dump_priv_trace_buffer(const struct net_device *ndev) { };
+static inline void erase_priv_trace_buffer(struct j1939_priv *priv) { };
+static inline void save_priv_trace_buffer(struct j1939_priv *priv, int delta) { };
+#endif
+
 static struct j1939_priv *j1939_priv_create(struct net_device *ndev)
 {
 	struct j1939_priv *priv;
@@ -137,6 +147,7 @@ static struct j1939_priv *j1939_priv_create(struct net_device *ndev)
 	priv->ndev = ndev;
 	kref_init(&priv->kref);
 	kref_init(&priv->rx_kref);
+	save_priv_trace_buffer(priv, 1);
 	dev_hold(ndev);
 
 	netdev_dbg(priv->ndev, "%s : 0x%p\n", __func__, priv);
@@ -164,17 +175,20 @@ static void __j1939_priv_release(struct kref *kref)
 	WARN_ON_ONCE(!list_empty(&priv->j1939_socks));
 
 	dev_put(ndev);
+	erase_priv_trace_buffer(priv);
 	kfree(priv);
 }
 
 void j1939_priv_put(struct j1939_priv *priv)
 {
+	save_priv_trace_buffer(priv, -1);
 	kref_put(&priv->kref, __j1939_priv_release);
 }
 
 void j1939_priv_get(struct j1939_priv *priv)
 {
 	kref_get(&priv->kref);
+	save_priv_trace_buffer(priv, 1);
 }
 
 static int j1939_can_rx_register(struct j1939_priv *priv)
@@ -282,6 +296,7 @@ struct j1939_priv *j1939_netdev_start(struct net_device *ndev)
 		kref_get(&priv_new->rx_kref);
 		mutex_unlock(&j1939_netdev_lock);
 		dev_put(ndev);
+		erase_priv_trace_buffer(priv);
 		kfree(priv);
 		return priv_new;
 	}
@@ -299,6 +314,7 @@ struct j1939_priv *j1939_netdev_start(struct net_device *ndev)
 	mutex_unlock(&j1939_netdev_lock);
 
 	dev_put(ndev);
+	erase_priv_trace_buffer(priv);
 	kfree(priv);
 
 	return ERR_PTR(ret);
@@ -364,6 +380,9 @@ static int j1939_netdev_notify(struct notifier_block *nb,
 	struct can_ml_priv *can_ml = can_get_ml_priv(ndev);
 	struct j1939_priv *priv;
 
+	if (msg == NETDEV_DEBUG_UNREGISTER)
+		dump_priv_trace_buffer(ndev);
+
 	if (!can_ml)
 		goto notify_done;
 
@@ -428,3 +447,79 @@ static __exit void j1939_module_exit(void)
 
 module_init(j1939_module_init);
 module_exit(j1939_module_exit);
+
+#ifdef CONFIG_NET_DEV_REFCNT_TRACKER
+
+#define PRIV_TRACE_BUFFER_SIZE 1024
+static struct priv_trace_buffer {
+	struct j1939_priv *priv; // no-ref
+	struct net_device *ndev; // no-ref
+	atomic_t count;
+	int nr_entries;
+	unsigned long entries[20];
+} priv_trace_buffer[PRIV_TRACE_BUFFER_SIZE];
+static bool priv_trace_buffer_exhausted;
+
+static void dump_priv_trace_buffer(const struct net_device *ndev)
+{
+	struct priv_trace_buffer *ptr;
+	int count, balance = 0;
+	int i;
+
+	for (i = 0; i < PRIV_TRACE_BUFFER_SIZE; i++) {
+		ptr = &priv_trace_buffer[i];
+		if (!ptr->priv || ptr->ndev != ndev)
+			continue;
+		count = atomic_read(&ptr->count);
+		balance += count;
+		pr_info("Call trace for %s@%p %+d at\n", ndev->name, ptr->priv, count);
+		stack_trace_print(ptr->entries, ptr->nr_entries, 4);
+	}
+	if (!priv_trace_buffer_exhausted)
+		pr_info("balance for %s@j1939_priv is %d\n", ndev->name, balance);
+	else
+		pr_info("balance for %s@j1939_priv is unknown\n", ndev->name);
+}
+
+static void erase_priv_trace_buffer(struct j1939_priv *priv)
+{
+	int i;
+
+	for (i = 0; i < PRIV_TRACE_BUFFER_SIZE; i++)
+		if (priv_trace_buffer[i].priv == priv)
+			priv_trace_buffer[i].priv = NULL;
+}
+
+static noinline void save_priv_trace_buffer(struct j1939_priv *priv, int delta)
+{
+	struct priv_trace_buffer *ptr;
+	unsigned long entries[ARRAY_SIZE(ptr->entries)];
+	unsigned long nr_entries;
+	int i;
+
+	if (in_nmi())
+		return;
+	nr_entries = stack_trace_save(entries, ARRAY_SIZE(ptr->entries), 1);
+	nr_entries = trim_netdev_trace(entries, nr_entries);
+	for (i = 0; i < PRIV_TRACE_BUFFER_SIZE; i++) {
+		ptr = &priv_trace_buffer[i];
+		if (ptr->priv == priv && ptr->nr_entries == nr_entries &&
+		    !memcmp(ptr->entries, entries, nr_entries * sizeof(unsigned long))) {
+			atomic_add(delta, &ptr->count);
+			return;
+		}
+	}
+	for (i = 0; i < PRIV_TRACE_BUFFER_SIZE; i++) {
+		ptr = &priv_trace_buffer[i];
+		if (!ptr->priv && !cmpxchg(&ptr->priv, NULL, priv)) {
+			ptr->ndev = priv->ndev;
+			atomic_set(&ptr->count, delta);
+			ptr->nr_entries = nr_entries;
+			memmove(ptr->entries, entries, nr_entries * sizeof(unsigned long));
+			return;
+		}
+	}
+	priv_trace_buffer_exhausted = true;
+}
+
+#endif
diff --git a/net/core/dev.c b/net/core/dev.c
index 2acfa44927da..c3a62c16fa15 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -1854,6 +1854,7 @@ const char *netdev_cmd_to_name(enum netdev_cmd cmd)
 	N(PRE_CHANGEADDR) N(OFFLOAD_XSTATS_ENABLE) N(OFFLOAD_XSTATS_DISABLE)
 	N(OFFLOAD_XSTATS_REPORT_USED) N(OFFLOAD_XSTATS_REPORT_DELTA)
 	N(XDP_FEAT_CHANGE)
+	N(DEBUG_UNREGISTER)
 	}
 #undef N
 	return "UNKNOWN_NETDEV_EVENT";
@@ -11429,6 +11430,14 @@ int netdev_refcnt_read(const struct net_device *dev)
 }
 EXPORT_SYMBOL(netdev_refcnt_read);
 
+#ifdef CONFIG_NET_DEV_REFCNT_TRACKER
+static void dump_netdev_trace_buffer(const struct net_device *dev);
+static void erase_netdev_trace_buffer(const struct net_device *dev);
+#else
+static inline void dump_netdev_trace_buffer(const struct net_device *dev) { }
+static inline void erase_netdev_trace_buffer(const struct net_device *dev) { }
+#endif
+
 int netdev_unregister_timeout_secs __read_mostly = 10;
 
 #define WAIT_REFS_MIN_MSECS 1
@@ -11502,11 +11511,16 @@ static struct net_device *netdev_wait_allrefs_any(struct list_head *list)
 
 		if (time_after(jiffies, warning_time +
 			       READ_ONCE(netdev_unregister_timeout_secs) * HZ)) {
+			rtnl_lock();
 			list_for_each_entry(dev, list, todo_list) {
 				pr_emerg("unregister_netdevice: waiting for %s to become free. Usage count = %d\n",
 					 dev->name, netdev_refcnt_read(dev));
 				ref_tracker_dir_print(&dev->refcnt_tracker, 10);
+				call_netdevice_notifiers(NETDEV_DEBUG_UNREGISTER, dev);
+				dump_netdev_trace_buffer(dev);
 			}
+			__rtnl_unlock();
+			rcu_barrier();
 
 			warning_time = jiffies;
 		}
@@ -11904,6 +11918,9 @@ struct net_device *alloc_netdev_mqs(int sizeof_priv, const char *name,
 
 	dev->priv_len = sizeof_priv;
 
+#ifdef CONFIG_NET_DEV_REFCNT_TRACKER
+	INIT_LIST_HEAD(&dev->netdev_trace_buffer_list);
+#endif
 	ref_tracker_dir_init(&dev->refcnt_tracker, 128, "netdev");
 #ifdef CONFIG_PCPU_DEV_REFCNT
 	dev->pcpu_refcnt = alloc_percpu(int);
@@ -12076,6 +12093,8 @@ void free_netdev(struct net_device *dev)
 
 	mutex_destroy(&dev->lock);
 
+	erase_netdev_trace_buffer(dev);
+
 	/*  Compatibility with error handling in drivers */
 	if (dev->reg_state == NETREG_UNINITIALIZED ||
 	    dev->reg_state == NETREG_DUMMY) {
@@ -13090,3 +13109,180 @@ static int __init net_dev_init(void)
 }
 
 subsys_initcall(net_dev_init);
+
+#ifdef CONFIG_NET_DEV_REFCNT_TRACKER
+
+#define NETDEV_TRACE_BUFFER_SIZE 32768
+static struct netdev_trace_buffer {
+	struct list_head list;
+	int prev_count;
+	atomic_t count;
+	int nr_entries;
+	unsigned long entries[20];
+} netdev_trace_buffer[NETDEV_TRACE_BUFFER_SIZE];
+static LIST_HEAD(netdev_trace_buffer_list);
+static DEFINE_SPINLOCK(netdev_trace_buffer_lock);
+static bool netdev_trace_buffer_exhausted;
+
+static int netdev_trace_buffer_init(void)
+{
+	int i;
+
+	for (i = 0; i < NETDEV_TRACE_BUFFER_SIZE; i++)
+		list_add_tail(&netdev_trace_buffer[i].list, &netdev_trace_buffer_list);
+	return 0;
+}
+pure_initcall(netdev_trace_buffer_init);
+
+static void dump_netdev_trace_buffer(const struct net_device *dev)
+{
+	struct netdev_trace_buffer *ptr;
+	int count, balance = 0, pos = 0;
+
+	list_for_each_entry_rcu(ptr, &dev->netdev_trace_buffer_list, list,
+				/* list elements can't go away. */ 1) {
+		pos++;
+		count = atomic_read(&ptr->count);
+		balance += count;
+		if (ptr->prev_count == count)
+			continue;
+		ptr->prev_count = count;
+		pr_info("Call trace for %s[%d] %+d at\n", dev->name, pos, count);
+		stack_trace_print(ptr->entries, ptr->nr_entries, 4);
+		cond_resched();
+	}
+	if (!netdev_trace_buffer_exhausted)
+		pr_info("balance as of %s[%d] is %d\n", dev->name, pos, balance);
+}
+
+static void erase_netdev_trace_buffer(const struct net_device *dev)
+{
+	struct netdev_trace_buffer *ptr;
+	unsigned long flags;
+
+	spin_lock_irqsave(&netdev_trace_buffer_lock, flags);
+	while (!list_empty(&dev->netdev_trace_buffer_list)) {
+		ptr = list_first_entry(&dev->netdev_trace_buffer_list, typeof(*ptr), list);
+		list_del(&ptr->list);
+		list_add_tail(&ptr->list, &netdev_trace_buffer_list);
+	}
+	spin_unlock_irqrestore(&netdev_trace_buffer_lock, flags);
+}
+
+#ifdef CONFIG_KALLSYMS
+static noinline unsigned long __find_trim(unsigned long *entries, int nr_entries, const char *name)
+{
+	int i;
+	char buffer[KSYM_SYMBOL_LEN];
+	const int len = strlen(name);
+
+	for (i = 0; i < nr_entries; i++) {
+		snprintf(buffer, sizeof(buffer), "%pS", (void *)entries[i]);
+		if (!strncmp(buffer, name, len) && buffer[len] == '+')
+			return entries[i];
+	}
+	return 0;
+}
+
+static unsigned long caller_handle_softirqs;
+static unsigned long caller_process_one_work;
+static unsigned long caller_ksys_unshare;
+static unsigned long caller___sys_bind;
+static unsigned long caller___sock_sendmsg;
+
+static int __init net_check_symbols(void)
+{
+	if (!kallsyms_lookup_name("handle_softirqs"))
+		caller_handle_softirqs = -1;
+	if (!kallsyms_lookup_name("process_one_work"))
+		caller_process_one_work = -1;
+	if (!kallsyms_lookup_name("ksys_unshare"))
+		caller_ksys_unshare = -1;
+	if (!kallsyms_lookup_name("__sys_bind"))
+		caller___sys_bind = -1;
+	if (!kallsyms_lookup_name("sock_sendmsg_nosec") &&
+	    !kallsyms_lookup_name("__sock_sendmsg"))
+		caller___sock_sendmsg = -1;
+	return 0;
+}
+late_initcall(net_check_symbols);
+#endif
+
+int trim_netdev_trace(unsigned long *entries, int nr_entries)
+{
+#ifdef CONFIG_KALLSYMS
+	int i;
+
+	if (in_softirq()) {
+		if (unlikely(!caller_handle_softirqs))
+			caller_handle_softirqs = __find_trim(entries, nr_entries,
+							     "handle_softirqs");
+		for (i = 0; i < nr_entries; i++)
+			if (entries[i] == caller_handle_softirqs)
+				return i + 1;
+	} else if (current->flags & PF_WQ_WORKER) {
+		if (unlikely(!caller_process_one_work))
+			caller_process_one_work = __find_trim(entries, nr_entries,
+							      "process_one_work");
+		for (i = 0; i < nr_entries; i++)
+			if (entries[i] == caller_process_one_work)
+				return i + 1;
+	} else {
+		if (unlikely(!caller_ksys_unshare))
+			caller_ksys_unshare = __find_trim(entries, nr_entries, "ksys_unshare");
+		if (unlikely(!caller___sys_bind))
+			caller___sys_bind = __find_trim(entries, nr_entries, "__sys_bind");
+		if (unlikely(!caller___sock_sendmsg)) {
+			caller___sock_sendmsg = __find_trim(entries, nr_entries,
+							    "sock_sendmsg_nosec");
+			if (!caller___sock_sendmsg)
+				caller___sock_sendmsg = __find_trim(entries, nr_entries,
+								    "__sock_sendmsg");
+		}
+		for (i = 0; i < nr_entries; i++)
+			if (entries[i] == caller_ksys_unshare ||
+			    entries[i] == caller___sys_bind ||
+			    entries[i] == caller___sock_sendmsg)
+				return i + 1;
+	}
+#endif
+	return nr_entries;
+}
+EXPORT_SYMBOL(trim_netdev_trace);
+
+void save_netdev_trace_buffer(struct net_device *dev, int delta)
+{
+	struct netdev_trace_buffer *ptr;
+	unsigned long entries[ARRAY_SIZE(ptr->entries)];
+	unsigned long nr_entries;
+	unsigned long flags;
+
+	if (in_nmi())
+		return;
+	nr_entries = stack_trace_save(entries, ARRAY_SIZE(ptr->entries), 1);
+	nr_entries = trim_netdev_trace(entries, nr_entries);
+	list_for_each_entry_rcu(ptr, &dev->netdev_trace_buffer_list, list,
+				/* list elements can't go away. */ 1) {
+		if (ptr->nr_entries == nr_entries &&
+		    !memcmp(ptr->entries, entries, nr_entries * sizeof(unsigned long))) {
+			atomic_add(delta, &ptr->count);
+			return;
+		}
+	}
+	spin_lock_irqsave(&netdev_trace_buffer_lock, flags);
+	if (!list_empty(&netdev_trace_buffer_list)) {
+		ptr = list_first_entry(&netdev_trace_buffer_list, typeof(*ptr), list);
+		list_del(&ptr->list);
+		ptr->prev_count = 0;
+		atomic_set(&ptr->count, delta);
+		ptr->nr_entries = nr_entries;
+		memmove(ptr->entries, entries, nr_entries * sizeof(unsigned long));
+		list_add_tail_rcu(&ptr->list, &dev->netdev_trace_buffer_list);
+	} else {
+		netdev_trace_buffer_exhausted = true;
+	}
+	spin_unlock_irqrestore(&netdev_trace_buffer_lock, flags);
+}
+EXPORT_SYMBOL(save_netdev_trace_buffer);
+
+#endif
diff --git a/net/core/lock_debug.c b/net/core/lock_debug.c
index 9e9fb25314b9..78d611bb6d1c 100644
--- a/net/core/lock_debug.c
+++ b/net/core/lock_debug.c
@@ -29,6 +29,7 @@ int netdev_debug_event(struct notifier_block *nb, unsigned long event,
 	case NETDEV_DOWN:
 	case NETDEV_REBOOT:
 	case NETDEV_UNREGISTER:
+	case NETDEV_DEBUG_UNREGISTER:
 	case NETDEV_CHANGEMTU:
 	case NETDEV_CHANGEADDR:
 	case NETDEV_PRE_CHANGEADDR:
diff --git a/net/socket.c b/net/socket.c
index e8892b218708..fce536d2d8b9 100644
--- a/net/socket.c
+++ b/net/socket.c
@@ -734,6 +734,10 @@ static inline int sock_sendmsg_nosec(struct socket *sock, struct msghdr *msg)
 	return ret;
 }
 
+#ifdef CONFIG_NET_DEV_REFCNT_TRACKER
+static noinline int __sock_sendmsg(struct socket *sock, struct msghdr *msg);
+#endif
+
 static int __sock_sendmsg(struct socket *sock, struct msghdr *msg)
 {
 	int err = security_socket_sendmsg(sock, msg,

Re: [syzbot] [net?] unregister_netdevice: waiting for DEV to become free (8)

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger any issue:

Reported-by: syzbot+881d65229ca4f9ae8c84@syzkaller.appspotmail.com
Tested-by: syzbot+881d65229ca4f9ae8c84@syzkaller.appspotmail.com

Tested on:

commit:         8b690556 Merge tag 'for-linus' of git://git.kernel.org..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=106da8b4580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=7fd2b6b29c6ab719
dashboard link: https://syzkaller.appspot.com/bug?extid=881d65229ca4f9ae8c84
compiler:       Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
patch:          https://syzkaller.appspot.com/x/patch.diff?x=13b77884580000

Note: testing is done by a robot and is best-effort only.

Re: unregister_netdevice: waiting for DEV to become free (8)

[Tetsuo Handa]

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

diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index d4e6e00bb90a..97862830f7d0 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -2102,6 +2102,8 @@ enum netdev_reg_state {
  *
  *	FIXME: cleanup struct net_device such that network protocol info
  *	moves out.
+ *
+ *	@netdev_trace_buffer_list: Linked list for debugging refcount leak.
  */
 
 struct net_device {
@@ -2257,6 +2259,9 @@ struct net_device {
 #if IS_ENABLED(CONFIG_TLS_DEVICE)
 	const struct tlsdev_ops *tlsdev_ops;
 #endif
+#ifdef CONFIG_NET_DEV_REFCNT_TRACKER
+	struct list_head	netdev_trace_buffer_list;
+#endif
 
 	unsigned int		operstate;
 	unsigned char		link_mode;
@@ -3185,6 +3190,7 @@ enum netdev_cmd {
 	NETDEV_OFFLOAD_XSTATS_REPORT_USED,
 	NETDEV_OFFLOAD_XSTATS_REPORT_DELTA,
 	NETDEV_XDP_FEAT_CHANGE,
+	NETDEV_DEBUG_UNREGISTER,
 };
 const char *netdev_cmd_to_name(enum netdev_cmd cmd);
 
@@ -4373,9 +4379,15 @@ static inline bool dev_nit_active(const struct net_device *dev)
 
 void dev_queue_xmit_nit(struct sk_buff *skb, struct net_device *dev);
 
+void save_netdev_trace_buffer(struct net_device *dev, int delta);
+int trim_netdev_trace(unsigned long *entries, int nr_entries);
+
 static inline void __dev_put(struct net_device *dev)
 {
 	if (dev) {
+#ifdef CONFIG_NET_DEV_REFCNT_TRACKER
+		save_netdev_trace_buffer(dev, -1);
+#endif
 #ifdef CONFIG_PCPU_DEV_REFCNT
 		this_cpu_dec(*dev->pcpu_refcnt);
 #else
@@ -4387,6 +4399,9 @@ static inline void __dev_put(struct net_device *dev)
 static inline void __dev_hold(struct net_device *dev)
 {
 	if (dev) {
+#ifdef CONFIG_NET_DEV_REFCNT_TRACKER
+		save_netdev_trace_buffer(dev, 1);
+#endif
 #ifdef CONFIG_PCPU_DEV_REFCNT
 		this_cpu_inc(*dev->pcpu_refcnt);
 #else
diff --git a/kernel/softirq.c b/kernel/softirq.c
index 77198911b8dd..5f435c1e48d8 100644
--- a/kernel/softirq.c
+++ b/kernel/softirq.c
@@ -576,6 +576,10 @@ static inline bool lockdep_softirq_start(void) { return false; }
 static inline void lockdep_softirq_end(bool in_hardirq) { }
 #endif
 
+#ifdef CONFIG_NET_DEV_REFCNT_TRACKER
+static noinline void handle_softirqs(bool ksirqd);
+#endif
+
 static void handle_softirqs(bool ksirqd)
 {
 	unsigned long end = jiffies + MAX_SOFTIRQ_TIME;
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index aeaec79bc09c..66cb4d8c00bb 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -3157,6 +3157,10 @@ static bool manage_workers(struct worker *worker)
 	return true;
 }
 
+#ifdef CONFIG_NET_DEV_REFCNT_TRACKER
+static noinline void process_one_work(struct worker *worker, struct work_struct *work);
+#endif
+
 /**
  * process_one_work - process single work
  * @worker: self
diff --git a/net/core/dev.c b/net/core/dev.c
index c1a9f7fdcffa..fbc205c82256 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -1874,6 +1874,7 @@ const char *netdev_cmd_to_name(enum netdev_cmd cmd)
 	N(PRE_CHANGEADDR) N(OFFLOAD_XSTATS_ENABLE) N(OFFLOAD_XSTATS_DISABLE)
 	N(OFFLOAD_XSTATS_REPORT_USED) N(OFFLOAD_XSTATS_REPORT_DELTA)
 	N(XDP_FEAT_CHANGE)
+	N(DEBUG_UNREGISTER)
 	}
 #undef N
 	return "UNKNOWN_NETDEV_EVENT";
@@ -11557,6 +11558,14 @@ int netdev_refcnt_read(const struct net_device *dev)
 }
 EXPORT_SYMBOL(netdev_refcnt_read);
 
+#ifdef CONFIG_NET_DEV_REFCNT_TRACKER
+static void dump_netdev_trace_buffer(const struct net_device *dev);
+static void erase_netdev_trace_buffer(const struct net_device *dev);
+#else
+static inline void dump_netdev_trace_buffer(const struct net_device *dev) { }
+static inline void erase_netdev_trace_buffer(const struct net_device *dev) { }
+#endif
+
 int netdev_unregister_timeout_secs __read_mostly = 10;
 
 #define WAIT_REFS_MIN_MSECS 1
@@ -11630,11 +11639,16 @@ static struct net_device *netdev_wait_allrefs_any(struct list_head *list)
 
 		if (time_after(jiffies, warning_time +
 			       READ_ONCE(netdev_unregister_timeout_secs) * HZ)) {
+			rtnl_lock();
 			list_for_each_entry(dev, list, todo_list) {
 				pr_emerg("unregister_netdevice: waiting for %s to become free. Usage count = %d\n",
 					 dev->name, netdev_refcnt_read(dev));
 				ref_tracker_dir_print(&dev->refcnt_tracker, 10);
+				call_netdevice_notifiers(NETDEV_DEBUG_UNREGISTER, dev);
+				dump_netdev_trace_buffer(dev);
 			}
+			__rtnl_unlock();
+			rcu_barrier();
 
 			warning_time = jiffies;
 		}
@@ -12032,6 +12046,9 @@ struct net_device *alloc_netdev_mqs(int sizeof_priv, const char *name,
 
 	dev->priv_len = sizeof_priv;
 
+#ifdef CONFIG_NET_DEV_REFCNT_TRACKER
+	INIT_LIST_HEAD(&dev->netdev_trace_buffer_list);
+#endif
 	ref_tracker_dir_init(&dev->refcnt_tracker, 128, "netdev");
 #ifdef CONFIG_PCPU_DEV_REFCNT
 	dev->pcpu_refcnt = alloc_percpu(int);
@@ -12204,6 +12221,8 @@ void free_netdev(struct net_device *dev)
 
 	mutex_destroy(&dev->lock);
 
+	erase_netdev_trace_buffer(dev);
+
 	/*  Compatibility with error handling in drivers */
 	if (dev->reg_state == NETREG_UNINITIALIZED ||
 	    dev->reg_state == NETREG_DUMMY) {
@@ -13306,3 +13325,171 @@ static int __init net_dev_init(void)
 }
 
 subsys_initcall(net_dev_init);
+
+#ifdef CONFIG_NET_DEV_REFCNT_TRACKER
+
+#define NETDEV_TRACE_BUFFER_SIZE 32768
+static struct netdev_trace_buffer {
+	struct list_head list;
+	int prev_count;
+	atomic_t count;
+	int nr_entries;
+	unsigned long entries[20];
+} netdev_trace_buffer[NETDEV_TRACE_BUFFER_SIZE];
+static LIST_HEAD(netdev_trace_buffer_list);
+static DEFINE_SPINLOCK(netdev_trace_buffer_lock);
+static bool netdev_trace_buffer_exhausted;
+
+static int netdev_trace_buffer_init(void)
+{
+	int i;
+
+	for (i = 0; i < NETDEV_TRACE_BUFFER_SIZE; i++)
+		list_add_tail(&netdev_trace_buffer[i].list, &netdev_trace_buffer_list);
+	return 0;
+}
+pure_initcall(netdev_trace_buffer_init);
+
+static void dump_netdev_trace_buffer(const struct net_device *dev)
+{
+	struct netdev_trace_buffer *ptr;
+	int count, balance = 0, pos = 0;
+
+	list_for_each_entry_rcu(ptr, &dev->netdev_trace_buffer_list, list,
+				/* list elements can't go away. */ 1) {
+		pos++;
+		count = atomic_read(&ptr->count);
+		balance += count;
+		if (ptr->prev_count == count)
+			continue;
+		ptr->prev_count = count;
+		pr_info("Call trace for %s[%d] %+d at\n", dev->name, pos, count);
+		stack_trace_print(ptr->entries, ptr->nr_entries, 4);
+		cond_resched();
+	}
+	if (!netdev_trace_buffer_exhausted)
+		pr_info("balance as of %s[%d] is %d\n", dev->name, pos, balance);
+}
+
+static void erase_netdev_trace_buffer(const struct net_device *dev)
+{
+	struct netdev_trace_buffer *ptr;
+	unsigned long flags;
+
+	spin_lock_irqsave(&netdev_trace_buffer_lock, flags);
+	while (!list_empty(&dev->netdev_trace_buffer_list)) {
+		ptr = list_first_entry(&dev->netdev_trace_buffer_list, typeof(*ptr), list);
+		list_del(&ptr->list);
+		list_add_tail(&ptr->list, &netdev_trace_buffer_list);
+	}
+	spin_unlock_irqrestore(&netdev_trace_buffer_lock, flags);
+}
+
+int trim_netdev_trace(unsigned long *entries, int nr_entries)
+{
+#ifdef CONFIG_KALLSYMS
+	char buffer[32] = { };
+	char *cp;
+	int i;
+
+	if (in_softirq()) {
+		static unsigned long __data_racy caller;
+
+		if (!caller) {
+			for (i = 0; i < nr_entries; i++) {
+				snprintf(buffer, sizeof(buffer) - 1, "%ps", (void *)entries[i]);
+				cp = strchr(buffer, ' ');
+				if (cp)
+					*cp = '\0';
+				if (!strcmp(buffer, "handle_softirqs")) {
+					caller = entries[i];
+					break;
+				}
+			}
+		}
+		for (i = 0; i < nr_entries; i++)
+			if (entries[i] == caller)
+				return i + 1;
+	} else if (current->flags & PF_WQ_WORKER) {
+		static unsigned long __data_racy caller;
+
+		if (!caller) {
+			for (i = 0; i < nr_entries; i++) {
+				snprintf(buffer, sizeof(buffer) - 1, "%ps", (void *)entries[i]);
+				cp = strchr(buffer, ' ');
+				if (cp)
+					*cp = '\0';
+				if (!strcmp(buffer, "process_one_work")) {
+					caller = entries[i];
+					break;
+				}
+			}
+		}
+		for (i = 0; i < nr_entries; i++)
+			if (entries[i] == caller)
+				return i + 1;
+	} else {
+		for (i = 0; i < nr_entries; i++) {
+			snprintf(buffer, sizeof(buffer) - 1, "%ps", (void *)entries[i]);
+			cp = strchr(buffer, ' ');
+			if (cp)
+				*cp = '\0';
+			if (buffer[0] == 'k') {
+				if (!strcmp(buffer, "ksys_unshare"))
+					return i + 1;
+			} else if (buffer[0] == 's') {
+				if (!strcmp(buffer, "sock_sendmsg_nosec") ||
+				    !strcmp(buffer, "sock_recvmsg_nosec"))
+					return i + 1;
+			} else if (buffer[0] == '_') {
+				if (!strcmp(buffer, "__sys_bind") ||
+				    !strcmp(buffer, "__sock_release") ||
+				    !strcmp(buffer, "__sys_bpf"))
+					return i + 1;
+			} else {
+				if (!strcmp(buffer, "do_sock_setsockopt"))
+					return i + 1;
+			}
+		}
+	}
+#endif
+	return nr_entries;
+}
+EXPORT_SYMBOL(trim_netdev_trace);
+
+void save_netdev_trace_buffer(struct net_device *dev, int delta)
+{
+	struct netdev_trace_buffer *ptr;
+	unsigned long entries[ARRAY_SIZE(ptr->entries)];
+	unsigned long nr_entries;
+	unsigned long flags;
+
+	if (in_nmi())
+		return;
+	nr_entries = stack_trace_save(entries, ARRAY_SIZE(ptr->entries), 1);
+	nr_entries = trim_netdev_trace(entries, nr_entries);
+	list_for_each_entry_rcu(ptr, &dev->netdev_trace_buffer_list, list,
+				/* list elements can't go away. */ 1) {
+		if (ptr->nr_entries == nr_entries &&
+		    !memcmp(ptr->entries, entries, nr_entries * sizeof(unsigned long))) {
+			atomic_add(delta, &ptr->count);
+			return;
+		}
+	}
+	spin_lock_irqsave(&netdev_trace_buffer_lock, flags);
+	if (!list_empty(&netdev_trace_buffer_list)) {
+		ptr = list_first_entry(&netdev_trace_buffer_list, typeof(*ptr), list);
+		list_del(&ptr->list);
+		ptr->prev_count = 0;
+		atomic_set(&ptr->count, delta);
+		ptr->nr_entries = nr_entries;
+		memmove(ptr->entries, entries, nr_entries * sizeof(unsigned long));
+		list_add_tail_rcu(&ptr->list, &dev->netdev_trace_buffer_list);
+	} else {
+		netdev_trace_buffer_exhausted = true;
+	}
+	spin_unlock_irqrestore(&netdev_trace_buffer_lock, flags);
+}
+EXPORT_SYMBOL(save_netdev_trace_buffer);
+
+#endif
diff --git a/net/core/lock_debug.c b/net/core/lock_debug.c
index 9e9fb25314b9..78d611bb6d1c 100644
--- a/net/core/lock_debug.c
+++ b/net/core/lock_debug.c
@@ -29,6 +29,7 @@ int netdev_debug_event(struct notifier_block *nb, unsigned long event,
 	case NETDEV_DOWN:
 	case NETDEV_REBOOT:
 	case NETDEV_UNREGISTER:
+	case NETDEV_DEBUG_UNREGISTER:
 	case NETDEV_CHANGEMTU:
 	case NETDEV_CHANGEADDR:
 	case NETDEV_PRE_CHANGEADDR:
diff --git a/net/socket.c b/net/socket.c
index 05952188127f..53c4b1fd3ef7 100644
--- a/net/socket.c
+++ b/net/socket.c
@@ -650,7 +650,11 @@ struct socket *sock_alloc(void)
 }
 EXPORT_SYMBOL(sock_alloc);
 
-static void __sock_release(struct socket *sock, struct inode *inode)
+static
+#ifdef CONFIG_NET_DEV_REFCNT_TRACKER
+noinline
+#endif
+void __sock_release(struct socket *sock, struct inode *inode)
 {
 	const struct proto_ops *ops = READ_ONCE(sock->ops);
 
@@ -722,7 +726,13 @@ static noinline void call_trace_sock_send_length(struct sock *sk, int ret,
 	trace_sock_send_length(sk, ret, 0);
 }
 
-static inline int sock_sendmsg_nosec(struct socket *sock, struct msghdr *msg)
+static
+#ifdef CONFIG_NET_DEV_REFCNT_TRACKER
+noinline
+#else
+inline
+#endif
+int sock_sendmsg_nosec(struct socket *sock, struct msghdr *msg)
 {
 	int ret = INDIRECT_CALL_INET(READ_ONCE(sock->ops)->sendmsg, inet6_sendmsg,
 				     inet_sendmsg, sock, msg,
@@ -1072,8 +1082,13 @@ static noinline void call_trace_sock_recv_length(struct sock *sk, int ret, int f
 	trace_sock_recv_length(sk, ret, flags);
 }
 
-static inline int sock_recvmsg_nosec(struct socket *sock, struct msghdr *msg,
-				     int flags)
+static
+#ifdef CONFIG_NET_DEV_REFCNT_TRACKER
+noinline
+#else
+inline
+#endif
+int sock_recvmsg_nosec(struct socket *sock, struct msghdr *msg, int flags)
 {
 	int ret = INDIRECT_CALL_INET(READ_ONCE(sock->ops)->recvmsg,
 				     inet6_recvmsg,
@@ -2532,9 +2547,12 @@ static int copy_msghdr_from_user(struct msghdr *kmsg,
 	return err < 0 ? err : 0;
 }
 
-static int ____sys_sendmsg(struct socket *sock, struct msghdr *msg_sys,
-			   unsigned int flags, struct used_address *used_address,
-			   unsigned int allowed_msghdr_flags)
+static
+#ifdef CONFIG_NET_DEV_REFCNT_TRACKER
+noinline
+#endif
+int ____sys_sendmsg(struct socket *sock, struct msghdr *msg_sys, unsigned int flags,
+		    struct used_address *used_address, unsigned int allowed_msghdr_flags)
 {
 	unsigned char ctl[sizeof(struct cmsghdr) + 20]
 				__aligned(sizeof(__kernel_size_t));

Re: [syzbot] [net?] unregister_netdevice: waiting for DEV to become free (8)

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger any issue:

Reported-by: syzbot+881d65229ca4f9ae8c84@syzkaller.appspotmail.com
Tested-by: syzbot+881d65229ca4f9ae8c84@syzkaller.appspotmail.com

Tested on:

commit:         11439c46 Linux 7.0-rc2
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=154a7472580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=894aa0415989af66
dashboard link: https://syzkaller.appspot.com/bug?extid=881d65229ca4f9ae8c84
compiler:       Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
patch:          https://syzkaller.appspot.com/x/patch.diff?x=12afd3e6580000

Note: testing is done by a robot and is best-effort only.