Date:   Tue, 21 Mar 2023 14:38:20 +0200
From:   Ville =?iso-8859-1?Q?Syrj=E4l=E4?= <ville.syrjala@linux.intel.com>
To:     "David E. Box" <david.e.box@linux.intel.com>
Cc:     nirmal.patel@linux.intel.com, jonathan.derrick@linux.dev,
        lorenzo.pieralisi@arm.com, hch@infradead.org, kw@linux.com,
        robh@kernel.org, bhelgaas@google.com, michael.a.bottini@intel.com,
        rafael@kernel.org, me@adhityamohan.in, linux-pci@vger.kernel.org,
        linux-kernel@vger.kernel.org, intel-gfx@lists.freedesktop.org
Subject: Re: [PATCH V10 4/4] PCI: vmd: Add quirk to configure PCIe ASPM and
 LTR
Message-ID: <ZBmlPIU4FIBU7HU1@intel.com>
References: <20230120031522.2304439-1-david.e.box@linux.intel.com>
 <20230120031522.2304439-5-david.e.box@linux.intel.com>
 <ZBjko/ifunIwsK2v@intel.com>
 <8675a80b311443d3c3ed99e09832bd07355bfcc2.camel@linux.intel.com>
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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 Syrj?l? 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 Syrj?l?
Intel