linux-kernel - Re: [PATCH V10 4/4] PCI: vmd: Add quirk to configure PCIe ASPM and LTR

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Message-ID: <8675a80b311443d3c3ed99e09832bd07355bfcc2.camel@linux.intel.com>
Date:   Mon, 20 Mar 2023 19:24:16 -0700
From:   "David E. Box" <david.e.box@...ux.intel.com>
To:     Ville Syrjälä <ville.syrjala@...ux.intel.com>
Cc:     nirmal.patel@...ux.intel.com, jonathan.derrick@...ux.dev,
        lorenzo.pieralisi@....com, hch@...radead.org, kw@...ux.com,
        robh@...nel.org, bhelgaas@...gle.com, michael.a.bottini@...el.com,
        rafael@...nel.org, me@...ityamohan.in, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org, intel-gfx@...ts.freedesktop.org
Subject: Re: [PATCH V10 4/4] PCI: vmd: Add quirk to configure PCIe ASPM and
 LTR

Hi,

On Tue, 2023-03-21 at 00:56 +0200, Ville Syrjälä wrote:
> On Thu, Jan 19, 2023 at 07:15:22PM -0800, David E. Box wrote:
> > +/*
> > + * Enable ASPM and LTR settings on devices that aren't configured by BIOS.
> > + */
> > +static int vmd_pm_enable_quirk(struct pci_dev *pdev, void *userdata)
> > +{
> > +       unsigned long features = *(unsigned long *)userdata;
> > +       u16 ltr = VMD_BIOS_PM_QUIRK_LTR;
> > +       u32 ltr_reg;
> > +       int pos;
> > +
> > +       if (!(features & VMD_FEAT_BIOS_PM_QUIRK))
> > +               return 0;
> > +
> > +       pci_enable_link_state(pdev, PCIE_LINK_STATE_ALL);

We call pci_enable_link_state from a callback that's run during pci_walk_bus()
which I see already acquires the semaphore. We've had this patch for well over a
year and I haven't seen this issue before. Is there a particular config needed
to reproduce it?

As far as a solution I think we can copy what __pci_disable_link_state() does
and add a bool argument so that we only do down/up on the semaphore when set to
true. Since we know we will in be the lock during the bus walk we can set it to
false.

David

> 
> Hi,
> 
> This is tripping lockdep on one our CI ADL machines.
> 
> https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_12814/bat-adlp-6/boot0.txt
> 
> <4>[   13.815380] ============================================
> <4>[   13.815382] WARNING: possible recursive locking detected
> <4>[   13.815384] 6.3.0-rc1-CI_DRM_12814-g4753bbc2a817+ #1 Not tainted
> <4>[   13.815386] --------------------------------------------
> <4>[   13.815387] swapper/0/1 is trying to acquire lock:
> <4>[   13.815389] ffffffff827ab0b0 (pci_bus_sem){++++}-{3:3}, at:
> pci_enable_link_state+0x69/0x1d0
> <4>[   13.815396] 
>                   but task is already holding lock:
> <4>[   13.815398] ffffffff827ab0b0 (pci_bus_sem){++++}-{3:3}, at:
> pci_walk_bus+0x24/0x90
> <4>[   13.815403] 
>                   other info that might help us debug this:
> <4>[   13.815404]  Possible unsafe locking scenario:
> 
> <4>[   13.815406]        CPU0
> <4>[   13.815407]        ----
> <4>[   13.815408]   lock(pci_bus_sem);
> <4>[   13.815410]   lock(pci_bus_sem);
> <4>[   13.815411] 
>                    *** DEADLOCK ***
> 
> <4>[   13.815413]  May be due to missing lock nesting notation
> 
> <4>[   13.815414] 2 locks held by swapper/0/1:
> <4>[   13.815416]  #0: ffff8881029511b8 (&dev->mutex){....}-{3:3}, at:
> __driver_attach+0xab/0x180
> <4>[   13.815422]  #1: ffffffff827ab0b0 (pci_bus_sem){++++}-{3:3}, at:
> pci_walk_bus+0x24/0x90
> <4>[   13.815426] 
>                   stack backtrace:
> <4>[   13.815428] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 6.3.0-rc1-
> CI_DRM_12814-g4753bbc2a817+ #1
> <4>[   13.815431] Hardware name: Intel Corporation Alder Lake Client
> Platform/AlderLake-P DDR4 RVP, BIOS ADLPFWI1.R00.3135.A00.2203251419
> 03/25/2022
> <4>[   13.815434] Call Trace:
> <4>[   13.815436]  <TASK>
> <4>[   13.815437]  dump_stack_lvl+0x64/0xb0
> <4>[   13.815443]  __lock_acquire+0x9b5/0x2550
> <4>[   13.815461]  lock_acquire+0xd7/0x330
> <4>[   13.815463]  ? pci_enable_link_state+0x69/0x1d0
> <4>[   13.815466]  down_read+0x3d/0x180
> <4>[   13.815480]  ? pci_enable_link_state+0x69/0x1d0
> <4>[   13.815482]  pci_enable_link_state+0x69/0x1d0
> <4>[   13.815485]  ? __pfx_vmd_pm_enable_quirk+0x10/0x10
> <4>[   13.815488]  vmd_pm_enable_quirk+0x49/0xb0
> <4>[   13.815490]  pci_walk_bus+0x6d/0x90
> <4>[   13.815492]  vmd_probe+0x75f/0x9d0
> <4>[   13.815495]  pci_device_probe+0x95/0x120
> <4>[   13.815498]  really_probe+0x164/0x3c0
> <4>[   13.815500]  ? __pfx___driver_attach+0x10/0x10
> <4>[   13.815503]  __driver_probe_device+0x73/0x170
> <4>[   13.815506]  driver_probe_device+0x19/0xa0
> <4>[   13.815508]  __driver_attach+0xb6/0x180
> <4>[   13.815511]  ? __pfx___driver_attach+0x10/0x10
> <4>[   13.815513]  bus_for_each_dev+0x77/0xd0
> <4>[   13.815516]  bus_add_driver+0x114/0x210
> <4>[   13.815518]  driver_register+0x5b/0x110
> <4>[   13.815520]  ? __pfx_vmd_drv_init+0x10/0x10
> <4>[   13.815523]  do_one_initcall+0x57/0x330
> <4>[   13.815527]  kernel_init_freeable+0x181/0x3a0
> <4>[   13.815529]  ? __pfx_kernel_init+0x10/0x10
> <4>[   13.815532]  kernel_init+0x15/0x120
> <4>[   13.815534]  ret_from_fork+0x29/0x50
> <4>[   13.815537]  </TASK>
>