[syzbot] [net?] WARNING in devlink_free (2)

[syzbot <syzbot+bbd81e1e2276c534dea1@syzkaller.appspotmail.com>]

Hello,

syzbot found the following issue on:

HEAD commit:    aa40afa831eb tcp: fix NULL pointer dereference when restar..
git tree:       net
console output: https://syzkaller.appspot.com/x/log.txt?x=1582ee3d580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=d44b06612b68f56
dashboard link: https://syzkaller.appspot.com/bug?extid=bbd81e1e2276c534dea1
compiler:       Debian clang version 22.1.8 (1~deb13u4), Debian LLD 22.1.8

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/2e5d84927015/disk-aa40afa8.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/e267992573f1/vmlinux-aa40afa8.xz
kernel image: https://storage.googleapis.com/syzbot-assets/828d3e3f2df4/bzImage-aa40afa8.xz

AI-generated root cause summary:
In netdevsim, switchdev eswitch mode can be enabled with zero VFs configured,
allowing userspace to create devlink rate nodes via netlink. However, during
device teardown or reload in nsim_dev_reload_destroy(), the cleanup call to
nsim_esw_legacy_enable()—which invokes devl_rate_nodes_destroy()—is
conditionally guarded by if (nsim_dev_get_vfs(nsim_dev)). When VFs were never
configured (num_vfs == 0), nsim_esw_legacy_enable() is bypassed, leaving
devlink_rate nodes in devlink->rate_list and triggering the
WARN_ON(devlink_rates_check(devlink, NULL, NULL)) sanity check in
devlink_free().

full analysis:  https://syzkaller.appspot.com/x/ai_root_cause?x=bbd81e1e2276c534dea1

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+bbd81e1e2276c534dea1@syzkaller.appspotmail.com

netdevsim netdevsim0 netdevsim0 (unregistering): unset [0, 0] type 1 family 0 port 8472 - 0
netdevsim netdevsim0 netdevsim0 (unregistering): unset [1, 0] type 2 family 0 port 6081 - 0
netdevsim netdevsim0 netdevsim0 (unregistering): unset [1, 1] type 2 family 0 port 20004 - 0
------------[ cut here ]------------
devlink_rates_check(devlink, NULL, NULL)
WARNING: net/devlink/core.c:544 at devlink_free+0x359/0x450 net/devlink/core.c:544, CPU#1: syz-executor/17425
Modules linked in:
CPU: 1 UID: 0 PID: 17425 Comm: syz-executor Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 11/06/2026
RIP: 0010:devlink_free+0x359/0x450 net/devlink/core.c:544
Code: 00 e8 fb 62 e8 f6 5b 41 5c 41 5d 41 5e 41 5f 5d c3 cc cc cc cc cc e8 e6 62 e8 f6 90 0f 0b 90 e9 02 fd ff ff e8 d8 62 e8 f6 90 <0f> 0b 90 e9 29 fd ff ff e8 ca 62 e8 f6 90 0f 0b 90 e9 59 fd ff ff
RSP: 0018:ffffc900038a78b8 EFLAGS: 00010293
RAX: ffffffff8ae0be08 RBX: ffff8880797aa000 RCX: ffff8880546a9f40
RDX: 0000000000000000 RSI: 00000000fffffff0 RDI: 0000000000000000
RBP: 00000000fffffff0 R08: ffffffff91be00bf R09: 1ffffffff237c017
R10: dffffc0000000000 R11: 0000000000000000 R12: dffffc0000000000
R13: 1ffff1100f2f5400 R14: ffff8880797aa1f8 R15: ffff8880797aa3e0
FS:  000055557a90f500(0000) GS:ffff888123508000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fd61b5f0ce0 CR3: 000000002bf22000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 nsim_drv_remove+0x146/0x170 drivers/net/netdevsim/dev.c:1736
 device_remove drivers/base/dd.c:617 [inline]
 __device_release_driver drivers/base/dd.c:1357 [inline]
 device_release_driver_internal+0x42b/0x7d0 drivers/base/dd.c:1380
 bus_remove_device+0x444/0x560 drivers/base/bus.c:678
 device_del+0x524/0x8f0 drivers/base/core.c:3967
 device_unregister+0x21/0xf0 drivers/base/core.c:4008
 nsim_bus_dev_del drivers/net/netdevsim/bus.c:488 [inline]
 del_device_store+0x2b5/0x370 drivers/net/netdevsim/bus.c:243
 kernfs_fop_write_iter+0x3a4/0x540 fs/kernfs/file.c:345
 new_sync_write fs/read_write.c:575 [inline]
 vfs_write+0x612/0xba0 fs/read_write.c:667
 ksys_write+0x150/0x270 fs/read_write.c:719
 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
 do_syscall_64+0x16a/0x530 arch/x86/entry/syscall_64.c:89
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7ffbf2169d0e
Code: 08 0f 85 a5 a8 ff ff 49 89 fb 48 89 f0 48 89 d7 48 89 ce 4c 89 c2 4d 89 ca 4c 8b 44 24 08 4c 8b 4c 24 10 4c 89 5c 24 08 0f 05 <c3> 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 80 00 00 00 00 48 83 ec 08
RSP: 002b:00007ffef50b4238 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 000055557a90f500 RCX: 00007ffbf2169d0e
RDX: 0000000000000001 RSI: 00007ffef50b42c0 RDI: 0000000000000005
RBP: 00007ffbf223891c R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000001
R13: 00007ffef50b42c0 R14: 00007ffef50b4b00 R15: 0000000000000003
 </TASK>


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