[v2,1/6] PCI/AER: Take severity mask into account while clearing error bits

Message ID 1529661494-20936-2-git-send-email-poza@codeaurora.org
State Superseded
Delegated to: Bjorn Helgaas
Headers show
Series
  • Fix issues and cleanup for ERR_FATAL and ERR_NONFATAL
Related show

Commit Message

Oza Pawandeep June 22, 2018, 9:58 a.m.
pci_cleanup_aer_uncorrect_error_status() is called by different slot_reset
callbacks in case of ERR_NONFATAL.

AER uncorrectable error status should take severity into account in order
to clear the bits, so that ERR_NONFATAL path does not clear the bit which
are marked with severity fatal.

Signed-off-by: Oza Pawandeep <poza@codeaurora.org>

Comments

Bjorn Helgaas July 17, 2018, 7:03 p.m. | #1
Hi Oza,

Thanks for doing this!

On Fri, Jun 22, 2018 at 05:58:09AM -0400, Oza Pawandeep wrote:
> pci_cleanup_aer_uncorrect_error_status() is called by different slot_reset
> callbacks in case of ERR_NONFATAL.

IIRC, the current strategy is:

  ERR_COR: log only
  ERR_NONFATAL: call driver callbacks (pci_error_handlers)
  ERR_FATAL: remove device and re-enumerate

So these slot_reset callbacks are only used for ERR_NONFATAL, which
are all uncorrectable errors, of course.

This patch makes it so that when the slot_reset callbacks call
pci_cleanup_aer_uncorrect_error_status(), we only clear the
bits set by ERR_NONFATAL events (this is determined by
PCI_ERR_UNCOR_SEVER).

That makes good sense to me.  All these status bits are RW1CS, so they
will be preserved across a reset but will be cleared when we
re-enumerate, in this path:

  pci_init_capabilities
    pci_aer_init
      pci_cleanup_aer_error_status_regs
      # clear all PCI_ERR_UNCOR_STATUS and PCI_ERR_COR_STATUS bits

> AER uncorrectable error status should take severity into account in order
> to clear the bits, so that ERR_NONFATAL path does not clear the bit which
> are marked with severity fatal.

Two comments:

1) Can you split this into two patches, one that changes
pci_cleanup_aer_uncorrect_error_status() so it looks like the error
clearing code in aer_error_resume(), and a second that factors out the
duplicate code?

2) Maybe use "sev" or "sever" instead of "mask" for the local
variable, since there is also a separate PCI_ERR_UNCOR_MASK register,
which is not involved here.

3) The "pci_cleanup_aer_uncorrect_error_status()" name no longer
really describes what this does.  Something like
"pci_aer_clear_nonfatal_status()" would be more descriptive.  But I
see you have a subsequent patch (which I haven't looked at yet) that
is related to this.

4) I don't think the driver slot_reset callbacks should be responsible
for clearing these AER status bits.  Can we clear them somewhere in
the pcie_do_nonfatal_recovery() path and remove these calls from the
drivers?

5) In principle, we should only read PCI_ERR_UNCOR_STATUS *once* per
device when handling an error.  We currently read it three times:

  aer_isr
    aer_isr_one_error
      find_source_device
        find_device_iter
          is_error_source
            read PCI_ERR_UNCOR_STATUS              # 1
      aer_process_err_devices
        get_device_error_info(e_info->dev[i])
          read PCI_ERR_UNCOR_STATUS                # 2
        handle_error_source
          pcie_do_nonfatal_recovery
            ...
              report_slot_reset
                driver->err_handler->slot_reset
                  pci_cleanup_aer_uncorrect_error_status
                    read PCI_ERR_UNCOR_STATUS      # 3

OK, that was more than two comments :)

> Signed-off-by: Oza Pawandeep <poza@codeaurora.org>
> 
> diff --git a/drivers/pci/pcie/aer.c b/drivers/pci/pcie/aer.c
> index a2e8838..d6cb1f0 100644
> --- a/drivers/pci/pcie/aer.c
> +++ b/drivers/pci/pcie/aer.c
> @@ -360,13 +360,16 @@ EXPORT_SYMBOL_GPL(pci_disable_pcie_error_reporting);
>  int pci_cleanup_aer_uncorrect_error_status(struct pci_dev *dev)
>  {
>  	int pos;
> -	u32 status;
> +	u32 status, mask;
>  
>  	pos = dev->aer_cap;
>  	if (!pos)
>  		return -EIO;
>  
> +	/* Clean AER Root Error Status */

s/Clean/Clear/ (I see you copied this from aer_error_resume(), and maybe
the second patch could remove or update that comment, too)

>  	pci_read_config_dword(dev, pos + PCI_ERR_UNCOR_STATUS, &status);
> +	pci_read_config_dword(dev, pos + PCI_ERR_UNCOR_SEVER, &mask);
> +	status &= ~mask; /* Clear corresponding nonfatal bits */
>  	if (status)
>  		pci_write_config_dword(dev, pos + PCI_ERR_UNCOR_STATUS, status);
>  
> @@ -1336,8 +1339,6 @@ static pci_ers_result_t aer_root_reset(struct pci_dev *dev)
>   */
>  static void aer_error_resume(struct pci_dev *dev)
>  {
> -	int pos;
> -	u32 status, mask;
>  	u16 reg16;
>  
>  	/* Clean up Root device status */
> @@ -1345,11 +1346,7 @@ static void aer_error_resume(struct pci_dev *dev)
>  	pcie_capability_write_word(dev, PCI_EXP_DEVSTA, reg16);
>  
>  	/* Clean AER Root Error Status */
> -	pos = dev->aer_cap;
> -	pci_read_config_dword(dev, pos + PCI_ERR_UNCOR_STATUS, &status);
> -	pci_read_config_dword(dev, pos + PCI_ERR_UNCOR_SEVER, &mask);
> -	status &= ~mask; /* Clear corresponding nonfatal bits */
> -	pci_write_config_dword(dev, pos + PCI_ERR_UNCOR_STATUS, status);
> +	pci_cleanup_aer_uncorrect_error_status(dev);
>  }
>  
>  static struct pcie_port_service_driver aerdriver = {
> -- 
> 2.7.4
>
Bjorn Helgaas July 17, 2018, 9:36 p.m. | #2
On Tue, Jul 17, 2018 at 02:03:29PM -0500, Bjorn Helgaas wrote:
> Hi Oza,
> 
> Thanks for doing this!
> 
> On Fri, Jun 22, 2018 at 05:58:09AM -0400, Oza Pawandeep wrote:
> > pci_cleanup_aer_uncorrect_error_status() is called by different slot_reset
> > callbacks in case of ERR_NONFATAL.
> 
> IIRC, the current strategy is:
> 
>   ERR_COR: log only
>   ERR_NONFATAL: call driver callbacks (pci_error_handlers)
>   ERR_FATAL: remove device and re-enumerate
> 
> So these slot_reset callbacks are only used for ERR_NONFATAL, which
> are all uncorrectable errors, of course.
> 
> This patch makes it so that when the slot_reset callbacks call
> pci_cleanup_aer_uncorrect_error_status(), we only clear the
> bits set by ERR_NONFATAL events (this is determined by
> PCI_ERR_UNCOR_SEVER).
> 
> That makes good sense to me.  All these status bits are RW1CS, so they
> will be preserved across a reset but will be cleared when we
> re-enumerate, in this path:
> 
>   pci_init_capabilities
>     pci_aer_init
>       pci_cleanup_aer_error_status_regs
>       # clear all PCI_ERR_UNCOR_STATUS and PCI_ERR_COR_STATUS bits
> 
> > AER uncorrectable error status should take severity into account in order
> > to clear the bits, so that ERR_NONFATAL path does not clear the bit which
> > are marked with severity fatal.
> 
> Two comments:
> 
> 1) Can you split this into two patches, one that changes
> pci_cleanup_aer_uncorrect_error_status() so it looks like the error
> clearing code in aer_error_resume(), and a second that factors out the
> duplicate code?
> 
> 2) Maybe use "sev" or "sever" instead of "mask" for the local
> variable, since there is also a separate PCI_ERR_UNCOR_MASK register,
> which is not involved here.

Let me back up a little here: I'm not asking you to do the things
below here.  They're just possible future things, so we can think
about them after this series.  And the things above are things I can
easily do myself.  So no action required from you, unless you think
I'm on the wrong track :)

> 3) The "pci_cleanup_aer_uncorrect_error_status()" name no longer
> really describes what this does.  Something like
> "pci_aer_clear_nonfatal_status()" would be more descriptive.  But I
> see you have a subsequent patch (which I haven't looked at yet) that
> is related to this.
> 
> 4) I don't think the driver slot_reset callbacks should be responsible
> for clearing these AER status bits.  Can we clear them somewhere in
> the pcie_do_nonfatal_recovery() path and remove these calls from the
> drivers?
> 
> 5) In principle, we should only read PCI_ERR_UNCOR_STATUS *once* per
> device when handling an error.  We currently read it three times:
> 
>   aer_isr
>     aer_isr_one_error
>       find_source_device
>         find_device_iter
>           is_error_source
>             read PCI_ERR_UNCOR_STATUS              # 1
>       aer_process_err_devices
>         get_device_error_info(e_info->dev[i])
>           read PCI_ERR_UNCOR_STATUS                # 2
>         handle_error_source
>           pcie_do_nonfatal_recovery
>             ...
>               report_slot_reset
>                 driver->err_handler->slot_reset
>                   pci_cleanup_aer_uncorrect_error_status
>                     read PCI_ERR_UNCOR_STATUS      # 3
> 
> OK, that was more than two comments :)
Oza Pawandeep July 18, 2018, 9:13 a.m. | #3
On 2018-07-18 03:06, Bjorn Helgaas wrote:
> On Tue, Jul 17, 2018 at 02:03:29PM -0500, Bjorn Helgaas wrote:
>> Hi Oza,
>> 
>> Thanks for doing this!
>> 
>> On Fri, Jun 22, 2018 at 05:58:09AM -0400, Oza Pawandeep wrote:
>> > pci_cleanup_aer_uncorrect_error_status() is called by different slot_reset
>> > callbacks in case of ERR_NONFATAL.
>> 
>> IIRC, the current strategy is:
>> 
>>   ERR_COR: log only
>>   ERR_NONFATAL: call driver callbacks (pci_error_handlers)
>>   ERR_FATAL: remove device and re-enumerate
>> 
>> So these slot_reset callbacks are only used for ERR_NONFATAL, which
>> are all uncorrectable errors, of course.
>> 
>> This patch makes it so that when the slot_reset callbacks call
>> pci_cleanup_aer_uncorrect_error_status(), we only clear the
>> bits set by ERR_NONFATAL events (this is determined by
>> PCI_ERR_UNCOR_SEVER).
>> 
>> That makes good sense to me.  All these status bits are RW1CS, so they
>> will be preserved across a reset but will be cleared when we
>> re-enumerate, in this path:
>> 
>>   pci_init_capabilities
>>     pci_aer_init
>>       pci_cleanup_aer_error_status_regs
>>       # clear all PCI_ERR_UNCOR_STATUS and PCI_ERR_COR_STATUS bits
>> 
>> > AER uncorrectable error status should take severity into account in order
>> > to clear the bits, so that ERR_NONFATAL path does not clear the bit which
>> > are marked with severity fatal.
>> 
>> Two comments:
>> 
>> 1) Can you split this into two patches, one that changes
>> pci_cleanup_aer_uncorrect_error_status() so it looks like the error
>> clearing code in aer_error_resume(), and a second that factors out the
>> duplicate code?
>> 
>> 2) Maybe use "sev" or "sever" instead of "mask" for the local
>> variable, since there is also a separate PCI_ERR_UNCOR_MASK register,
>> which is not involved here.
> 
> Let me back up a little here: I'm not asking you to do the things
> below here.  They're just possible future things, so we can think
> about them after this series.  And the things above are things I can
> easily do myself.  So no action required from you, unless you think
> I'm on the wrong track :)

I agree with your points, and have taken them into account for future 
series reference as well.

what about PATCH-2 of this series ?
that clears ERR_FATAL bits, but as you said, during re-enumeration
pci_init_capabilities
      pci_aer_init
        pci_cleanup_aer_error_status_regs
        # clear all PCI_ERR_UNCOR_STATUS and PCI_ERR_COR_STATUS bits

but that should clear the ERR_FATAL of the devices beneath.

PATCH2: we are doing it for BRIDGE where we think where ERR_FATAL was 
reported by bridge and the problem is with downstream link.
if ((service == PCIE_PORT_SERVICE_AER) &&
	    (dev->hdr_type == PCI_HEADER_TYPE_BRIDGE)) {
		/*
		 * If the error is reported by a bridge, we think this error
		 * is related to the downstream link of the bridge, so we
		 * do error recovery on all subordinates of the bridge instead
		 * of the bridge and clear the error status of the bridge.
		 */
		pci_cleanup_aer_uncorrect_error_status(dev);
	}


so overall, I think all the patches are required, if you have comments 
please let me know.
so far I see that, no action is required from me.

> 
>> 3) The "pci_cleanup_aer_uncorrect_error_status()" name no longer
>> really describes what this does.  Something like
>> "pci_aer_clear_nonfatal_status()" would be more descriptive.  But I
>> see you have a subsequent patch (which I haven't looked at yet) that
>> is related to this.
>> 
>> 4) I don't think the driver slot_reset callbacks should be responsible
>> for clearing these AER status bits.  Can we clear them somewhere in
>> the pcie_do_nonfatal_recovery() path and remove these calls from the
>> drivers?
>> 
>> 5) In principle, we should only read PCI_ERR_UNCOR_STATUS *once* per
>> device when handling an error.  We currently read it three times:
>> 
>>   aer_isr
>>     aer_isr_one_error
>>       find_source_device
>>         find_device_iter
>>           is_error_source
>>             read PCI_ERR_UNCOR_STATUS              # 1
>>       aer_process_err_devices
>>         get_device_error_info(e_info->dev[i])
>>           read PCI_ERR_UNCOR_STATUS                # 2
>>         handle_error_source
>>           pcie_do_nonfatal_recovery
>>             ...
>>               report_slot_reset
>>                 driver->err_handler->slot_reset
>>                   pci_cleanup_aer_uncorrect_error_status
>>                     read PCI_ERR_UNCOR_STATUS      # 3
>> 
>> OK, that was more than two comments :)

Patch

diff --git a/drivers/pci/pcie/aer.c b/drivers/pci/pcie/aer.c
index a2e8838..d6cb1f0 100644
--- a/drivers/pci/pcie/aer.c
+++ b/drivers/pci/pcie/aer.c
@@ -360,13 +360,16 @@  EXPORT_SYMBOL_GPL(pci_disable_pcie_error_reporting);
 int pci_cleanup_aer_uncorrect_error_status(struct pci_dev *dev)
 {
 	int pos;
-	u32 status;
+	u32 status, mask;
 
 	pos = dev->aer_cap;
 	if (!pos)
 		return -EIO;
 
+	/* Clean AER Root Error Status */
 	pci_read_config_dword(dev, pos + PCI_ERR_UNCOR_STATUS, &status);
+	pci_read_config_dword(dev, pos + PCI_ERR_UNCOR_SEVER, &mask);
+	status &= ~mask; /* Clear corresponding nonfatal bits */
 	if (status)
 		pci_write_config_dword(dev, pos + PCI_ERR_UNCOR_STATUS, status);
 
@@ -1336,8 +1339,6 @@  static pci_ers_result_t aer_root_reset(struct pci_dev *dev)
  */
 static void aer_error_resume(struct pci_dev *dev)
 {
-	int pos;
-	u32 status, mask;
 	u16 reg16;
 
 	/* Clean up Root device status */
@@ -1345,11 +1346,7 @@  static void aer_error_resume(struct pci_dev *dev)
 	pcie_capability_write_word(dev, PCI_EXP_DEVSTA, reg16);
 
 	/* Clean AER Root Error Status */
-	pos = dev->aer_cap;
-	pci_read_config_dword(dev, pos + PCI_ERR_UNCOR_STATUS, &status);
-	pci_read_config_dword(dev, pos + PCI_ERR_UNCOR_SEVER, &mask);
-	status &= ~mask; /* Clear corresponding nonfatal bits */
-	pci_write_config_dword(dev, pos + PCI_ERR_UNCOR_STATUS, status);
+	pci_cleanup_aer_uncorrect_error_status(dev);
 }
 
 static struct pcie_port_service_driver aerdriver = {