linux-kernel - Re: [PATCH] PCI / PM: Restore the status of PCI devices across hibernation

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Message-ID: <20170616194559.GD11129@bhelgaas-glaptop.roam.corp.google.com>
Date:   Fri, 16 Jun 2017 14:45:59 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Chen Yu <yu.c.chen@...el.com>
Cc:     "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Len Brown <len.brown@...el.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Rui Zhang <rui.zhang@...el.com>,
        Ying Huang <ying.huang@...el.com>, linux-pci@...r.kernel.org,
        linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] PCI / PM: Restore the status of PCI devices across
 hibernation

On Thu, May 25, 2017 at 04:49:07PM +0800, Chen Yu wrote:
> Currently we saw a lot of "No irq handler" errors during hibernation,
> which caused the system hang finally:
> 
> [  710.141581] ata4.00: qc timeout (cmd 0xec)
> [  710.147135] ata4.00: failed to IDENTIFY (I/O error, err_mask=0x4)
> [  710.154593] ata4.00: revalidation failed (errno=-5)
> [  710.468124] ata4: SATA link up 6.0 Gbps (SStatus 133 SControl 300)
> [  710.477746] do_IRQ: 31.151 No irq handler for vector
> 
> According to above logs, there is an interrupt triggered and it is
> dispatched to CPU31 with a vector number 151, but there is no handler
> for it, thus this irq will not get acked and caused irq flood which kill
> the system. To be more specific, the 31.151 is an interrupt from the ahci
> host controller.
> 
> After some investigation, the reason why this issue is triggered is
> because the thaw_noirq() function does not restore the MSI/MSIX settings
> across hibernation.
> 
> The scenario is illustrated below:
> 
> 1. Before the hibernation starts, the irq 34 is the handler for the ahci device,
>    which is binded on cpu31.
> 2. Hibernation starts, the ahci device is put into low power state.
> 3. All the nonboot CPUs are put offline, so the irq 34 has to be migrated to
>    the last alive one - CPU0.
> 4. After the snapshot has been created, all the nonboot CPUs are brought up again,
>    the CPU affinity for IRQ 34 remains to be 0.
> 5. ahci device are put into D0.
> 6. The snapshot is written to the disk.
> 
> The issue is triggered in step 6, in theory the ahci interrupt should be
> delivered to CPU0, however the actually result is that this interrupt is
> delivered to the original CPU31 instead, which cause the "No irq handler" issue.
> 
> Ying Huang has has provided a clue that, in step 3 it is possible that the writing
> to the register might not take effect as the PCI devices have been put suspended.
> Actually it is true:
> In step 3, the irq 34 affinity is supposed to be modified from 31 to 0,
> but actually it did not. In __pci_write_msi_msg(), if the device is already
> in low power state, the low level msi message entry will not be updated
> but cached. So in theory during the device restore process, the cached msi
> modification information should be written back to the hardware, and this
> is what pci_restore_msi_state() do during normal suspend-resume.
> But this is not the case for hibernation, pci_restore_msi_state() is not
> invoked currently, to be more specific, pci_restore_state() is not invoked
> in pci_pm_thaw_noirq(), although pci_save_state() has saved the necessary
> pci cached information in pci_pm_freeze_noirq().
> 
> This patch tries to restore the pci status for the device during hibernation,
> otherwise the status might be lost across hibernation(for example, the MSI/MSIX
> message settings), which might cause problems during hibernation.
> 
> Suggested-by: Ying Huang <ying.huang@...el.com>
> Suggested-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> Cc: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> Cc: Bjorn Helgaas <bhelgaas@...gle.com>
> Cc: Len Brown <len.brown@...el.com>
> Cc: Dan Williams <dan.j.williams@...el.com>
> Cc: Rui Zhang <rui.zhang@...el.com>
> Cc: Ying Huang <ying.huang@...el.com>
> Cc: linux-pci@...r.kernel.org
> Cc: linux-pm@...r.kernel.org
> Cc: linux-kernel@...r.kernel.org
> Signed-off-by: Chen Yu <yu.c.chen@...el.com>

Added a stable tag and applied with Rafael's reviewed-by to pci/pm for
v4.13, thanks!

pci_restore_state() restores a lot of stuff besides MSI/MSI-X: PCIe
device, link, slot control, ATS, VC, BARs, ACS, IOV.  I guess I'm a
little surprised that we haven't noticed more issues if all these
things were broken.

> ---
>  drivers/pci/pci-driver.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/pci/pci-driver.c b/drivers/pci/pci-driver.c
> index 192e7b6..b399fa3 100644
> --- a/drivers/pci/pci-driver.c
> +++ b/drivers/pci/pci-driver.c
> @@ -964,6 +964,7 @@ static int pci_pm_thaw_noirq(struct device *dev)
>  		return pci_legacy_resume_early(dev);
>  
>  	pci_update_current_state(pci_dev, PCI_D0);
> +	pci_restore_state(pci_dev);
>  
>  	if (drv && drv->pm && drv->pm->thaw_noirq)
>  		error = drv->pm->thaw_noirq(dev);
> -- 
> 2.7.4
>