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Date:   Fri, 9 Oct 2020 05:05:54 +0100
From:   Hedi Berriche <hedi.berriche@hpe.com>
To:     "Raj, Ashok" <ashok.raj@intel.com>
Cc:     Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@linux.intel.com>,
        linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org,
        Russ Anderson <rja@hpe.com>,
        Bjorn Helgaas <bhelgaas@google.com>,
        Joerg Roedel <jroedel@suse.com>, stable@kernel.org
Subject: Re: [PATCH v1 1/1] PCI/ERR: don't clobber status after reset_link()
Message-ID: <20201009040554.GB2365427@sarge.linuxathome.me>
Mail-Followup-To: "Raj, Ashok" <ashok.raj@intel.com>,
        Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>,
        linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org,
        Russ Anderson <rja@hpe.com>, Bjorn Helgaas <bhelgaas@google.com>,
        Joerg Roedel <jroedel@suse.com>, stable@kernel.org
References: <20201009025251.2360659-1-hedi.berriche@hpe.com>
 <20201009034614.GB60852@otc-nc-03>
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On Fri, Oct 09, 2020 at 04:46 Raj, Ashok wrote:

Hi Ashok,

Thanks for looking into this.

>On Fri, Oct 09, 2020 at 03:52:51AM +0100, Hedi Berriche wrote:
>> Commit 6d2c89441571 ("PCI/ERR: Update error status after reset_link()")
>> changed pcie_do_recovery() so that status is updated with the return
>> value from reset_link(); this was to fix the problem where we would
>> wrongly report recovery failure, despite a successful reset_link(),
>> whenever the initial error status is PCI_ERS_RESULT_DISCONNECT or
>> PCI_ERS_RESULT_NO_AER_DRIVER.
>>
>> Unfortunately this breaks the flow of pcie_do_recovery() as it prevents
>
>What is the reference to "this breaks" above?

The code change introduced by commit 6d2c89441571; would

     "this code change" instead of "this breaks"

work better? If not, I can also rephrase the whole paragraph along the following lines:

Commit 6d2c89441571 ("PCI/ERR: Update error status after reset_link()") breaks the flow
of pcie_do_recovery() as it prevents the actions needed when the initial error is
PCI_ERS_RESULT_CAN_RECOVER or PCI_ERS_RESULT_NEED_RESET from taking place which causes
error recovery to fail.

... and do away with the first paragraph.

>> the actions needed when the initial error is PCI_ERS_RESULT_CAN_RECOVER
>> or PCI_ERS_RESULT_NEED_RESET from taking place which causes error
>> recovery to fail.
>>
>> Don't clobber status after reset_link() to restore the intended flow in
>> pcie_do_recovery().
>>
>> Fix the original problem by saving the return value from reset_link()
>> and use it later on to decide whether error recovery should be deemed
>> successful in the scenarios where the initial error status is
>> PCI_ERS_RESULT_{DISCONNECT,NO_AER_DRIVER}.
>
>I would rather rephrase the above to make it clear what is being proposed.
>Since the description seems to talk about the old problem and new solution
>all mixed up.

OK; will do that to clarify that what's being proposed here is:

     1. fix the regression introduced by commit 6d2c89441571
     2. address the problem that commit 6d2c89441571 aimed to fix

>> Fixes: 6d2c89441571 ("PCI/ERR: Update error status after reset_link()")
>> Signed-off-by: Hedi Berriche <hedi.berriche@hpe.com>
>> Cc: Russ Anderson <rja@hpe.com>
>> Cc: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
>> Cc: Bjorn Helgaas <bhelgaas@google.com>
>> Cc: Ashok Raj <ashok.raj@intel.com>
>> Cc: Keith Busch <keith.busch@intel.com>
>> Cc: Joerg Roedel <jroedel@suse.com>
>>
>> Cc: stable@kernel.org # v5.7+
>> ---
>>  drivers/pci/pcie/err.c | 13 ++++++++++---
>>  1 file changed, 10 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/pci/pcie/err.c b/drivers/pci/pcie/err.c
>> index c543f419d8f9..dbd0b56bd6c1 100644
>> --- a/drivers/pci/pcie/err.c
>> +++ b/drivers/pci/pcie/err.c
>> @@ -150,7 +150,7 @@ pci_ers_result_t pcie_do_recovery(struct pci_dev *dev,
>>  			pci_channel_state_t state,
>>  			pci_ers_result_t (*reset_link)(struct pci_dev *pdev))
>>  {
>> -	pci_ers_result_t status = PCI_ERS_RESULT_CAN_RECOVER;
>> +	pci_ers_result_t post_reset_status, status = PCI_ERS_RESULT_CAN_RECOVER;
>
>why call it post_reset_status?

Perhaps post_reset_status is not a great choice; would reset_result or reset_link_result be better?

Cheers,
Hedi.

>
>>  	struct pci_bus *bus;
>>
>>  	/*
>> @@ -165,8 +165,8 @@ pci_ers_result_t pcie_do_recovery(struct pci_dev *dev,
>>  	pci_dbg(dev, "broadcast error_detected message\n");
>>  	if (state == pci_channel_io_frozen) {
>>  		pci_walk_bus(bus, report_frozen_detected, &status);
>> -		status = reset_link(dev);
>> -		if (status != PCI_ERS_RESULT_RECOVERED) {
>> +		post_reset_status = reset_link(dev);
>> +		if (post_reset_status != PCI_ERS_RESULT_RECOVERED) {
>>  			pci_warn(dev, "link reset failed\n");
>>  			goto failed;
>>  		}
>> @@ -174,6 +174,13 @@ pci_ers_result_t pcie_do_recovery(struct pci_dev *dev,
>>  		pci_walk_bus(bus, report_normal_detected, &status);
>>  	}
>>
>> +	if ((status == PCI_ERS_RESULT_DISCONNECT ||
>> +	     status == PCI_ERS_RESULT_NO_AER_DRIVER) &&
>> +	     post_reset_status == PCI_ERS_RESULT_RECOVERED) {
>> +		/* error recovery succeeded thanks to reset_link() */
>> +		status = PCI_ERS_RESULT_RECOVERED;
>> +	}
>> +
>>  	if (status == PCI_ERS_RESULT_CAN_RECOVER) {
>>  		status = PCI_ERS_RESULT_RECOVERED;
>>  		pci_dbg(dev, "broadcast mmio_enabled message\n");
>> --
>> 2.28.0
>>

-- 
Be careful of reading health books, you might die of a misprint.
	-- Mark Twain