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

Ville Syrjälä
2023-03-21T12:38:36Z

On Mon, Mar 20, 2023 at 07:24:16PM -0700, David E. Box wrote:
> 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?

Not sure what would affect it, beyond the normal PROVE_LOCKING=y.

This is the .config our CI uses:
https://gitlab.freedesktop.org/gfx-ci/i915-infra/-/blob/master/kconfig/debug

>
> 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>
> >

--
Ville Syrjälä
Intel