linux-kernel - Re: [PATCH 1/2] igc: don't rd/wr iomem when PCI is removed

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Date:   Mon, 5 Jul 2021 15:23:21 +0800
From:   Aaron Ma <aaron.ma@...onical.com>
To:     Pali Rohár <pali@...nel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Krzysztof Wilczyński <kw@...ux.com>
Cc:     jesse.brandeburg@...el.com, anthony.l.nguyen@...el.com,
        davem@...emloft.net, kuba@...nel.org,
        intel-wired-lan@...ts.osuosl.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
        Marek Behún <kabel@...nel.org>
Subject: Re: [PATCH 1/2] igc: don't rd/wr iomem when PCI is removed


On 7/4/21 10:28 PM, Pali Rohár wrote:
> + Bjorn, Krzysztof and linux-pci
> 
> On Friday 02 July 2021 12:51:19 Aaron Ma wrote:
>> Check PCI state when rd/wr iomem.
>> Implement wr32 function as rd32 too.
>>
>> When unplug TBT dock with i225, rd/wr PCI iomem will cause error log:
>> Trace:
>> BUG: unable to handle page fault for address: 000000000000b604
>> Oops: 0000 [#1] SMP NOPTI
>> RIP: 0010:igc_rd32+0x1c/0x90 [igc]
>> Call Trace:
>> igc_ptp_suspend+0x6c/0xa0 [igc]
>> igc_ptp_stop+0x12/0x50 [igc]
>> igc_remove+0x7f/0x1c0 [igc]
>> pci_device_remove+0x3e/0xb0
>> __device_release_driver+0x181/0x240
>>
>> Signed-off-by: Aaron Ma <aaron.ma@...onical.com>
>> ---
>>   drivers/net/ethernet/intel/igc/igc_main.c | 16 ++++++++++++++++
>>   drivers/net/ethernet/intel/igc/igc_regs.h |  7 ++-----
>>   2 files changed, 18 insertions(+), 5 deletions(-)
>>
>> diff --git a/drivers/net/ethernet/intel/igc/igc_main.c b/drivers/net/ethernet/intel/igc/igc_main.c
>> index f1adf154ec4a..606b72cb6193 100644
>> --- a/drivers/net/ethernet/intel/igc/igc_main.c
>> +++ b/drivers/net/ethernet/intel/igc/igc_main.c
>> @@ -5292,6 +5292,10 @@ u32 igc_rd32(struct igc_hw *hw, u32 reg)
>>   	u8 __iomem *hw_addr = READ_ONCE(hw->hw_addr);
>>   	u32 value = 0;
>>   
>> +	if (igc->pdev &&
>> +		igc->pdev->error_state == pci_channel_io_perm_failure)
> 
> Hello! This code pattern and commit message looks like that we could use
> pci_dev_is_disconnected() helper function for checking if device is
> still connected or was disconnected.
> 
> Apparently pci_dev_is_disconnected() is defined only in private header
> file drivers/pci/pci.h and not in public include/linux/pci.h.
> 
> Aaron: can you check if pci_dev_is_disconnected() is really something
> which should be used and it helps you?
> 

Hi Pali,

How about using pci_channel_offline instead?
It's ready and also safe for frozen state, and verified on hw.

> Bjorn, Krzysztof: what do you think about lifting helper function
> pci_dev_is_disconnected() to be available to all drivers and not only in
> PCI subsystem?
> 
> I think that such helper function makes driver code more readable and
> can be useful also for other drivers which are checking if return value
> is all F's.
> 
>> +		return 0;
> 
> Aaron: should not you return all F's on error? Because few lines below
> in this function is returned value with all F's when PCIe link lost.
> 

If you agree with the above change, I can fix it to "return -1" in v2.

Thanks for your comments,
Aaron


>> +
>>   	value = readl(&hw_addr[reg]);
> 
> Anyway, this code looks to be racy. When pci_channel_io_perm_failure is
> set (e.g. by hotplug interrupt) after checking for pdev->error_state and
> prior executing above readl() then mentioned fatal error still occurs.
> 
>>   
>>   	/* reads should not return all F's */
>> @@ -5308,6 +5312,18 @@ u32 igc_rd32(struct igc_hw *hw, u32 reg)
>>   	return value;
>>   }
>>   
>> +void igc_wr32(struct igc_hw *hw, u32 reg, u32 val)
>> +{
>> +	struct igc_adapter *igc = container_of(hw, struct igc_adapter, hw);
>> +	u8 __iomem *hw_addr = READ_ONCE(hw->hw_addr);
>> +
>> +	if (igc->pdev &&
>> +		igc->pdev->error_state == pci_channel_io_perm_failure)
>> +		return;
>> +
>> +	writel((val), &hw_addr[(reg)]);
>> +}
>> +
>>   int igc_set_spd_dplx(struct igc_adapter *adapter, u32 spd, u8 dplx)
>>   {
>>   	struct igc_mac_info *mac = &adapter->hw.mac;
>> diff --git a/drivers/net/ethernet/intel/igc/igc_regs.h b/drivers/net/ethernet/intel/igc/igc_regs.h
>> index cc174853554b..eb4be87d0e8b 100644
>> --- a/drivers/net/ethernet/intel/igc/igc_regs.h
>> +++ b/drivers/net/ethernet/intel/igc/igc_regs.h
>> @@ -260,13 +260,10 @@ struct igc_hw;
>>   u32 igc_rd32(struct igc_hw *hw, u32 reg);
>>   
>>   /* write operations, indexed using DWORDS */
>> -#define wr32(reg, val) \
>> -do { \
>> -	u8 __iomem *hw_addr = READ_ONCE((hw)->hw_addr); \
>> -	writel((val), &hw_addr[(reg)]); \
>> -} while (0)
>> +void igc_wr32(struct igc_hw *hw, u32 reg, u32 val);
>>   
>>   #define rd32(reg) (igc_rd32(hw, reg))
>> +#define wr32(reg, val) (igc_wr32(hw, reg, val))
>>   
>>   #define wrfl() ((void)rd32(IGC_STATUS))
>>   
>> -- 
>> 2.30.2
>>