[syzbot] [pci?] WARNING in pci_add_new_bus

[syzbot <syzbot+ea7278bdcb20a491495b@syzkaller.appspotmail.com>]

Hello,

syzbot found the following issue on:

HEAD commit:    36aad21d50d1 Merge tag 'ksmbd-for-7.4-rc1-part2' of git://..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1501662d580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=37ec6334ca3b8e94
dashboard link: https://syzkaller.appspot.com/bug?extid=ea7278bdcb20a491495b
compiler:       gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=127a2cb1580000

Downloadable assets:
disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/d900f083ada3/non_bootable_disk-36aad21d.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/d729f75149c3/vmlinux-36aad21d.xz
kernel image: https://storage.googleapis.com/syzbot-assets/f2cbf16f3d26/bzImage-36aad21d.xz

AI-generated root cause summary:
In drivers/pci/probe.c:pci_alloc_child_bus(), device_register(&child->dev)
failure is checked using WARN_ON(ret < 0). When device_register() fails due to
normal runtime resource exhaustion (such as -ENOMEM, triggered in syzkaller by
fault injection via /proc/thread-self/fail-nth), this check emits a spurious
kernel WARNING. Furthermore, pci_alloc_child_bus() assigns bridge->subordinate =
child and updates bridge->resource[...].name before calling device_register();
when device_register() fails, put_device(&child->dev) frees the child bus via
release_pcibus_dev(), but bridge->subordinate and bridge->resource names are not
reset to NULL, leaving dangling pointers to freed memory.

full analysis:  https://syzkaller.appspot.com/x/ai_root_cause?x=ea7278bdcb20a491495b

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+ea7278bdcb20a491495b@syzkaller.appspotmail.com

R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fc139c26038 R14: 00007fc139c25fa0 R15: 00007ffe91ac8be8
 </TASK>
------------[ cut here ]------------
ret < 0
WARNING: drivers/pci/probe.c:1272 at pci_alloc_child_bus drivers/pci/probe.c:1272 [inline], CPU#2: syz.3.21/6134
WARNING: drivers/pci/probe.c:1272 at pci_add_new_bus+0xda4/0x12e0 drivers/pci/probe.c:1293, CPU#2: syz.3.21/6134
Modules linked in:
CPU: 2 UID: 0 PID: 6134 Comm: syz.3.21 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
RIP: 0010:pci_alloc_child_bus drivers/pci/probe.c:1272 [inline]
RIP: 0010:pci_add_new_bus+0xda4/0x12e0 drivers/pci/probe.c:1293
Code: fd ff ff e8 1e 5e 95 fc 44 8b 74 24 18 31 ff 44 89 f6 e8 7f 58 95 fc 45 85 f6 74 dc 45 31 f6 e9 71 fd ff ff e8 fd 5d 95 fc 90 <0f> 0b 90 48 8b 3c 24 e8 c0 c6 03 01 31 db e9 92 fb ff ff e8 e4 5d
RSP: 0018:ffffc90003e3f988 EFLAGS: 00010293
RAX: 0000000000000000 RBX: ffff888050413000 RCX: 0000000000000000
RDX: ffff88802e362580 RSI: ffffffff8578e803 RDI: 0000000000000005
RBP: 00000000fffffff4 R08: 0000000000000000 R09: 00000000fffffff4
R10: ffff888050413153 R11: 0000000000000001 R12: ffff888024497000
R13: 1ffff920007c7f36 R14: ffff8880504130dc R15: ffff8880565849a0
FS:  00007fc13a9046c0(0000) GS:ffff8880d467f000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fc1399ecc40 CR3: 0000000035790000 CR4: 0000000000352ef0
Call Trace:
 <TASK>
 pci_scan_bridge_extend+0x9e3/0xb70 drivers/pci/probe.c:1473
 pci_scan_child_bus_extend+0x449/0x7b0 drivers/pci/probe.c:3138
 pci_scan_child_bus drivers/pci/probe.c:3216 [inline]
 pci_rescan_bus+0x18/0x40 drivers/pci/probe.c:3507
 rescan_store+0xfb/0x130 drivers/pci/pci-sysfs.c:474
 bus_attr_store+0x74/0xb0 drivers/base/bus.c:172
 sysfs_kf_write+0xf2/0x150 fs/sysfs/file.c:145
 kernfs_fop_write_iter+0x3e0/0x5f0 fs/kernfs/file.c:345
 new_sync_write fs/read_write.c:595 [inline]
 vfs_write+0x6af/0x1050 fs/read_write.c:687
 ksys_write+0x12a/0x250 fs/read_write.c:739
 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
 do_syscall_64+0x123/0x790 arch/x86/entry/syscall_64.c:84
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fc13999f559
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 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 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fc13a904028 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007fc139c25fa0 RCX: 00007fc13999f559
RDX: 000000000000001e RSI: 0000200000000280 RDI: 0000000000000004
RBP: 00007fc139a36b50 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fc139c26038 R14: 00007fc139c25fa0 R15: 00007ffe91ac8be8
 </TASK>


---
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