linux-kernel - Re: [PATCH V2]nvme-pci: Fixes EEH failure on ppc

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Message-ID: <75ec663f-1598-7ad8-a23a-0524edc6e575@grimberg.me>
Date:   Thu, 8 Feb 2018 18:39:10 +0200
From:   Sagi Grimberg <sagi@...mberg.me>
To:     Keith Busch <keith.busch@...el.com>, wenxiong@...ux.vnet.ibm.com
Cc:     axboe@...com, linux-kernel@...r.kernel.org,
        linux-nvme@...ts.infradead.org, wenxiong@...ibm.com
Subject: Re: [PATCH V2]nvme-pci: Fixes EEH failure on ppc

>> @@ -1189,6 +1183,12 @@ static enum blk_eh_timer_return nvme_timeout(struct request *req, bool reserved)
>>   	struct nvme_command cmd;
>>   	u32 csts = readl(dev->bar + NVME_REG_CSTS);
>>   
>> +	/* If PCI error recovery process is happening, we cannot reset or
>> +	 * the recovery mechanism will surely fail.
>> +	 */
>> +	if (pci_channel_offline(to_pci_dev(dev->dev)))
>> +		return BLK_EH_RESET_TIMER;
> 
> So reading csts is what triggers EEH to be detected and get the channel
> set offline? If so, don't we need a memory barrier before calling
> pci_channel_offline? Otherwise it looks like the compiler optimization
> could reorder these.

I think you're right.