Re: [PATCH] PCI/sysfs: Fix race in pci sysfs creation
From: Alexander Stein
Date: Tue Dec 12 2023 - 02:19:18 EST
Hi Saurabh,
thanks for the patch.
Am Samstag, 9. Dezember 2023, 04:46:16 CET schrieb Saurabh Sengar:
> Currently there is a race in calling pci_create_resource_files function
> from two different therads, first therad is triggered by pci_sysfs_init
> from the late initcall where as the second thread is initiated by
> pci_bus_add_devices from the respective PCI drivers probe.
>
> The synchronization between these threads relies on the sysfs_initialized
> flag. However, in pci_sysfs_init, sysfs_initialized is set right before
> calling pci_create_resource_files which is wrong as it can create race
> condition with pci_bus_add_devices threads. Fix this by setting
> sysfs_initialized flag at the end of pci_sysfs_init and direecly call the
Small typo here: direecly -> directly
> pci_create_resource_files function from it.
>
> There can be an additional case where driver probe is so delayed that
> pci_bus_add_devices is called after the sysfs is created by pci_sysfs_init.
> In such cases, attempting to access already existing sysfs resources is
> unnecessary. Fix this by adding a check for sysfs attributes and return
> if they are already allocated.
>
> In both cases, the consequence will be the removal of sysfs resources that
> were appropriately allocated by pci_sysfs_init following the warning below.
I'm not sure if this is the way to go. Unfortunately I can't trigger this
error on my imx6 platform at the moment (apparently timing is off).
But reading [1] again, the most expressive way is that pci_bus_add_devices()
needs to wait until pci_sysfs_init() has passed.
Best regards,
Alexander
[1] https://lore.kernel.org/lkml/a1cca367-52b6-a6b1-fb01-890cad39fd29@xxxxxxxx/
>
> [ 3.376688] sysfs: cannot create duplicate filename
> '/devices/LNXSYSTM:00/LNXSYBUS:00/PNP0A03:00/device:07/VMBUS:01/47505500-00
> 01-0000-3130-444531454238/pci0001:00/0001:00:00.0/resource0' [ 3.385103]
> CPU: 3 PID: 9 Comm: kworker/u8:0 Not tainted 5.15.0-1046-azure
> #53~20.04.1-Ubuntu [ 3.389585] Hardware name: Microsoft Corporation
> Virtual Machine/Virtual Machine, BIOS 090008 12/07/2018 [ 3.394663]
> Workqueue: events_unbound async_run_entry_fn
> [ 3.397687] Call Trace:
> [ 3.399312] <TASK>
> [ 3.400780] dump_stack_lvl+0x38/0x4d
> [ 3.402998] dump_stack+0x10/0x16
> [ 3.406050] sysfs_warn_dup.cold+0x17/0x2b
> [ 3.408476] sysfs_add_file_mode_ns+0x17b/0x190
> [ 3.411072] sysfs_create_bin_file+0x64/0x90
> [ 3.413514] pci_create_attr+0xc7/0x260
> [ 3.415827] pci_create_resource_files+0x6f/0x150
> [ 3.418455] pci_create_sysfs_dev_files+0x18/0x30
> [ 3.421136] pci_bus_add_device+0x30/0x70
> [ 3.423512] pci_bus_add_devices+0x31/0x70
> [ 3.425958] hv_pci_probe+0x4ce/0x640
> [ 3.428106] vmbus_probe+0x67/0x90
> [ 3.430121] really_probe.part.0+0xcb/0x380
> [ 3.432516] really_probe+0x40/0x80
> [ 3.434581] __driver_probe_device+0xe8/0x140
> [ 3.437119] driver_probe_device+0x23/0xb0
> [ 3.439504] __driver_attach_async_helper+0x31/0x90
> [ 3.442296] async_run_entry_fn+0x33/0x120
> [ 3.444666] process_one_work+0x225/0x3d0
> [ 3.447043] worker_thread+0x4d/0x3e0
> [ 3.449233] ? process_one_work+0x3d0/0x3d0
> [ 3.451632] kthread+0x12a/0x150
> [ 3.453583] ? set_kthread_struct+0x50/0x50
> [ 3.456103] ret_from_fork+0x22/0x30
>
> Signed-off-by: Saurabh Sengar <ssengar@xxxxxxxxxxxxxxxxxxx>
> ---
> There has been earlier attempts to fix this problem, below are the patches
> for reference of these attempts.
> 1.
> https://lore.kernel.org/linux-pci/20230316103036.1837869-1-alexander.stein@
> ew.tq-group.com/T/#u 2.
> https://lwn.net/ml/linux-kernel/20230316091540.494366-1-alexander.stein@ew.
> tq-group.com/
>
> Bug details: https://bugzilla.kernel.org/show_bug.cgi?id=215515
>
> drivers/pci/pci-sysfs.c | 9 +++++++--
> 1 file changed, 7 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/pci/pci-sysfs.c b/drivers/pci/pci-sysfs.c
> index f2909ae93f2f..a31f6f2cf309 100644
> --- a/drivers/pci/pci-sysfs.c
> +++ b/drivers/pci/pci-sysfs.c
> @@ -1230,6 +1230,10 @@ static int pci_create_resource_files(struct pci_dev
> *pdev) if (!pci_resource_len(pdev, i))
> continue;
>
> + /* Check if resource already allocated and proceed no
further */
> + if (pdev->res_attr[i] || pdev->res_attr_wc[i])
> + return 0;
> +
> retval = pci_create_attr(pdev, i, 0);
> /* for prefetchable resources, create a WC mappable file
*/
> if (!retval && arch_can_pci_mmap_wc() &&
> @@ -1411,9 +1415,8 @@ static int __init pci_sysfs_init(void)
> struct pci_bus *pbus = NULL;
> int retval;
>
> - sysfs_initialized = 1;
> for_each_pci_dev(pdev) {
> - retval = pci_create_sysfs_dev_files(pdev);
> + retval = pci_create_resource_files(pdev);
> if (retval) {
> pci_dev_put(pdev);
> return retval;
> @@ -1423,6 +1426,8 @@ static int __init pci_sysfs_init(void)
> while ((pbus = pci_find_next_bus(pbus)))
> pci_create_legacy_files(pbus);
>
> + sysfs_initialized = 1;
> +
> return 0;
> }
> late_initcall(pci_sysfs_init);
--
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