Re: PCI/ASPM locking regression in 6.7-final (was: Re: [PATCH] Revert "PCI/ASPM: Remove pcie_aspm_pm_state_change()")

Bjorn Helgaas
2024-01-22T18:26:17Z

On Mon, Jan 22, 2024 at 11:53:35AM +0100, Johan Hovold wrote:
> Hi Bjorn,
>
> I never got a reply to this one so resending with updated Subject in
> case it got buried in your inbox.

I did see it but decided it was better to fix the problem with resume
causing an unintended reboot, even though fixing that meant breaking
lockdep again, since I don't think we have user reports of the
potential deadlock lockdep finds.

08d0cc5f3426 ("PCI/ASPM: Remove pcie_aspm_pm_state_change()") was a
start at fixing other problems and also improving the ASPM style, so I
hope somebody steps up to fix both it and the lockdep issue. I
haven't looked at it enough to have a preference for *how* to fix it.

Bjorn

> On Mon, Jan 08, 2024 at 09:39:07AM +0100, Johan Hovold wrote:
>
> > On Tue, Jan 02, 2024 at 05:25:50PM -0600, Bjorn Helgaas wrote:
> > > From: Bjorn Helgaas <bhelgaas@google.com>
> > >
> > > This reverts commit 08d0cc5f34265d1a1e3031f319f594bd1970976c.
> > >
> > > Michael reported that when attempting to resume from suspend to RAM on ASUS
> > > mini PC PN51-BB757MDE1 (DMI model: MINIPC PN51-E1), 08d0cc5f3426
> > > ("PCI/ASPM: Remove pcie_aspm_pm_state_change()") caused a 12-second delay
> > > with no output, followed by a reboot.
> > >
> > > Workarounds include:
> > >
> > > - Reverting 08d0cc5f3426 ("PCI/ASPM: Remove pcie_aspm_pm_state_change()")
> > > - Booting with "pcie_aspm=off"
> > > - Booting with "pcie_aspm.policy=performance"
> > > - "echo 0 | sudo tee /sys/bus/pci/devices/0000:03:00.0/link/l1_aspm"
> > > before suspending
> > > - Connecting a USB flash drive
> > >
> > > Fixes: 08d0cc5f3426 ("PCI/ASPM: Remove pcie_aspm_pm_state_change()")
> > > Reported-by: Michael Schaller <michael@5challer.de>
> > > Link: https://lore.kernel.org/r/76c61361-b8b4-435f-a9f1-32b716763d62@5challer.de
> > > Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
> > > Cc: <stable@vger.kernel.org>
> > > ---
> >
> > > +/* @pdev: the root port or switch downstream port */
> > > +void pcie_aspm_pm_state_change(struct pci_dev *pdev)
> > > +{
> > > + struct pcie_link_state *link = pdev->link_state;
> > > +
> > > + if (aspm_disabled || !link)
> > > + return;
> > > + /*
> > > + * Devices changed PM state, we should recheck if latency
> > > + * meets all functions' requirement
> > > + */
> > > + down_read(&pci_bus_sem);
> > > + mutex_lock(&aspm_lock);
> > > + pcie_update_aspm_capable(link->root);
> > > + pcie_config_aspm_path(link);
> > > + mutex_unlock(&aspm_lock);
> > > + up_read(&pci_bus_sem);
> > > +}
> >
> > This function is now restored in 6.7 final and is called in paths which
> > already hold the pci_bus_sem as reported by lockdep (see splat below).
> >
> > This can potentially lead to a deadlock and specifically prevents using
> > lockdep on Qualcomm platforms.
> >
> > Not sure if you want to propagate whether the bus semaphore is held to
> > pcie_aspm_pm_state_change() or if there was some alternative to
> > restoring this function which should be explored instead.
>
> So to summarise, this patch, which is now commit
>
> f93e71aea6c6 ("Revert "PCI/ASPM: Remove pcie_aspm_pm_state_change()"")
>
> introduced a regression in 6.7-final for Qualcomm platforms (and some
> Intel platforms) similar to the one recently fixed by commit
>
> f352ce999260 ("PCI: qcom: Fix potential deadlock when enabling ASPM").
>
> Johan
>
>
> #regzbot introduced: f93e71aea6c6
>
> > ============================================
> > WARNING: possible recursive locking detected
> > 6.7.0 #40 Not tainted
> > --------------------------------------------
> > kworker/u16:5/90 is trying to acquire lock:
> > ffffacfa78ced000 (pci_bus_sem){++++}-{3:3}, at: pcie_aspm_pm_state_change+0x58/0xdc
> > pcieport 0002:00:00.0: PME: Signaling with IRQ 197
> >
> > but task is already holding lock:
> > ffffacfa78ced000 (pci_bus_sem){++++}-{3:3}, at: pci_walk_bus+0x34/0xbc
> >
> > other info that might help us debug this:
> > Possible unsafe locking scenario:
> >
> > CPU0
> > ----
> > lock(pci_bus_sem);
> > lock(pci_bus_sem);
> >
> > *** DEADLOCK ***
> >
> > May be due to missing lock nesting notation
> >
> > 4 locks held by kworker/u16:5/90:
> > #0: ffff06c5c0008d38 ((wq_completion)events_unbound){+.+.}-{0:0}, at: process_one_work+0x150/0x53c
> > #1: ffff800081c0bdd0 ((work_completion)(&entry->work)){+.+.}-{0:0}, at: process_one_work+0x150/0x53c
> > #2: ffff06c5c0b7d0f8 (&dev->mutex){....}-{3:3}, at: __driver_attach_async_helper+0x3c/0xf4
> > #3: ffffacfa78ced000 (pci_bus_sem){++++}-{3:3}, at: pci_walk_bus+0x34/0xbc
> >
> > stack backtrace:
> > CPU: 1 PID: 90 Comm: kworker/u16:5 Not tainted 6.7.0 #40
> > Hardware name: LENOVO 21BYZ9SRUS/21BYZ9SRUS, BIOS N3HET53W (1.25 ) 10/12/2022
> > Workqueue: events_unbound async_run_entry_fn
> > Call trace:
> > dump_backtrace+0x9c/0x11c
> > show_stack+0x18/0x24
> > dump_stack_lvl+0x60/0xac
> > dump_stack+0x18/0x24
> > print_deadlock_bug+0x25c/0x348
> > __lock_acquire+0x10a4/0x2064
> > lock_acquire+0x1e8/0x318
> > down_read+0x60/0x184
> > pcie_aspm_pm_state_change+0x58/0xdc
> > pci_set_full_power_state+0xa8/0x114
> > pci_set_power_state+0xc4/0x120
> > qcom_pcie_enable_aspm+0x1c/0x3c [pcie_qcom]
> > pci_walk_bus+0x64/0xbc
> > qcom_pcie_host_post_init_2_7_0+0x28/0x34 [pcie_qcom]