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>
>
