linux-kernel - Re: [BUG] sysfs: duplicate resource file creation during PCIe rescan

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Message-ID: <142957c5-64c2-47cd-846f-6ff0654aa3b7@h-partners.com>
Date: Sat, 30 Aug 2025 11:10:40 +0800
From: moubingquan <moubingquan@...artners.com>
To: <bhelgaas@...gle.com>
CC: <ilpo.jarvinen@...ux.intel.com>, <lukas@...ner.de>, linux-arm
	<linux-arm-kernel@...ts.infradead.org>, linux-kernl
	<linux-kernel@...r.kernel.org>, linux-pci <linux-pci@...r.kernel.org>,
	fanghao <fanghao11@...wei.com>, gaozhihao <gaozhihao6@...artners.com>,
	lujunhua <lujunhua7@...artners.com>, shenyang <shenyang39@...wei.com>,
	wushanping <wushanping@...wei.com>, zengtao <prime.zeng@...ilicon.com>,
	<jonathan.cameron@...wei.com>
Subject: Re: [BUG] sysfs: duplicate resource file creation during PCIe rescan

Friendly ping ...

On 8/11/2025 10:12 AM, moubingquan wrote:
> Hello everyone, does anyone have any ideas on how to approach this problem。
> 
> On 7/29/2025 9:13 AM, moubingquan wrote:
>> Hi all,
>>
>> When uninstalling the driver on the ARM64 platform and invoking `sriov_disable()`,
>> another thread simultaneously performed `echo 1 > /sys/bus/pci/rescan`,
>> which resulted in a call trace error (`sysfs: cannot create duplicate filename`) when subsequently loading the driver.
>>
>> Under certain multi-threaded scenarios (e.g. VF teardown + PCI rescan triggered in parallel),
>> The following sequence may result in files appearing in sysfs that should not exist:
>>
>> 1. sriov_disable() uninstalls VFs and removes the corresponding VF files in sysfs.
>> 2.At the same time, when rescan_store() rescan the entire PCI device tree,
>> there is a possibility that VF files that should have been deleted are added back,
>> resulting in VF files in sysfs that should have been removed but were not.
>>
>> Tested on:
>> - Kernel version: Linux version 6.15.0-rc4+ (phisik3@...50-163-153-ARM-openEuler22-3)
>> - Platform: ARM64 (Huawei Kunpeng920)
>> - Repro steps:
>> 1.Thread A unloads the driver and VF (requires calling sriov_disable()).
>> 2.Thread B calls `echo 1 > /sys/bus/pci/rescan `
>>
>> The system will report a call trace as follows:
>>
>> sysfs: cannot create duplicate filename '/devices/pci0000:3c/0000:3c:01.0/0000:3e:00.2/resource2'
>> CPU: 138 UID: 0 PID: 11067 Comm: sh Kdump: loaded Tainted: G      D W  O        6.15.0-rc4+ #1 PREEMPT
>> Tainted: [D]=DIE, [W]=WARN, [O]=OOT_MODULE
>> Call trace:
>>   show_stack+0x20/0x38 (C)
>>   dump_stack_lvl+0x80/0xf8
>>   dump_stack+0x18/0x28
>>   sysfs_warn_dup+0x6c/0x90
>>   sysfs_add_bin_file_mode_ns+0x12c/0x178
>>   sysfs_create_bin_file+0x7c/0xb8
>>   pci_create_attr+0x104/0x1b0
>>   pci_create_resource_files.part.0+0x50/0xd0
>>   pci_create_sysfs_dev_files+0x30/0x50
>>   pci_bus_add_device+0x40/0x120
>>   pci_bus_add_devices+0x40/0x98
>>   pci_bus_add_devices+0x6c/0x98
>>   pci_rescan_bus+0x38/0x58
>>   rescan_store+0x80/0xb0
>>   bus_attr_store+0x2c/0x48
>>   sysfs_kf_write+0x84/0xa8
>>   kernfs_fop_write_iter+0x120/0x1b8
>>   vfs_write+0x338/0x3f8
>>   ksys_write+0x70/0x110
>>   __arm64_sys_write+0x24/0x38
>>   invoke_syscall+0x50/0x120
>>   el0_svc_common.constprop.0+0xc8/0xf0
>>   do_el0_svc+0x24/0x38
>>   el0_svc+0x34/0xf0
>>   el0t_64_sync_handler+0xc8/0xd0
>>   el0t_64_sync+0x1ac/0x1b0
>>
>> The general analysis and corresponding code are as follows:
>>
>> drivers/pci/iov.c
>>
>> 736 static void sriov_disable(struct pci_dev *dev)
>> 737 {
>> 738         struct pci_sriov *iov = dev->sriov;
>> 739
>> 740         if (!iov->num_VFs)
>> 741                 return;
>> 742
>> 743         sriov_del_vfs(dev);
>> 744         iov->ctrl &= ~(PCI_SRIOV_CTRL_VFE | PCI_SRIOV_CTRL_MSE);
>> 745         pci_cfg_access_lock(dev);
>> 746         pci_write_config_word(dev, iov->pos + PCI_SRIOV_CTRL, iov->ctrl);
>> 747         ssleep(1);
>> 748         pci_cfg_access_unlock(dev);
>> 749
>> 750         pcibios_sriov_disable(dev);
>> 751
>> 752         if (iov->link != dev->devfn)
>> 753                 sysfs_remove_link(&dev->dev.kobj, "dep_link");
>> 754
>> 755         iov->num_VFs = 0;
>> 756         pci_iov_set_numvfs(dev, 0);
>> 757 }
>>
>> sriov_disable() will unload the VF and remove its files from sysfs.
>>
>> drivers/pci/pci-sysfs.c
>>
>>   435 static ssize_t rescan_store(const struct bus_type *bus, const char *buf, size_t count)
>>   436 {
>>   437         unsigned long val;
>>   438         struct pci_bus *b = NULL;
>>   439
>>   440         if (kstrtoul(buf, 0, &val) < 0)
>>   441                 return -EINVAL;
>>   442
>>   443         if (val) {
>>   444                 pci_lock_rescan_remove();
>>   445                 while ((b = pci_find_next_bus(b)) != NULL)
>>   446                         pci_rescan_bus(b);
>>   447                 pci_unlock_rescan_remove();
>>   448         }
>>   449         return count;
>>   450 }
>>   451 static BUS_ATTR_WO(rescan);
>>
>> The `rescan_store()` function will scan the entire PCI bus, including the relevant sysfs files for the aforementioned VFs.
>>
>> Initially, it seemed that directly adding the pci_lock_rescan_remove() lock to sriov_disable() could solve the problem.
>> However, it was later discovered that this might lead to a deadlock issue (because the remove_store() function would call sriov_disable(), causing a deadlock).
>>
>> drivers/pci/pci-sysfs.c
>>
>>   487 static ssize_t remove_store(struct device *dev, struct device_attribute *attr,
>>   488                             const char *buf, size_t count)
>>   489 {
>>   490         unsigned long val;
>>   491
>>   492         if (kstrtoul(buf, 0, &val) < 0)
>>   493                 return -EINVAL;
>>   494
>>   495         if (val && device_remove_file_self(dev, attr))
>>   496
>>          //Subsequently, sriov_disable() will be invoked.
>>                  pci_stop_and_remove_bus_device_locked(to_pci_dev(dev));
>>   497         return count;
>>   498 }
>>   499 static DEVICE_ATTR_IGNORE_LOCKDEP(remove, 0220, NULL,
>>   500                                   remove_store);
>>
>> The function `pci_stop_and_remove_bus_device_locked()` acquires the `pci_lock_rescan_remove()` lock and subsequently calls `sriov_disable()`.
>> If the lock is added within `sriov_disable()`, it could lead to a deadlock.
>>
>> Should we add a new lock to address this issue, or are there any other ideas? I would like to consult and discuss this with everyone.
>>
>> Thanks,
>> Bingquan Mou <moubingquan@...artners.com>
>