linux-kernel - Re: [PATCH 1/2] libsas: Don't process sas events in static works

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Date:   Mon, 22 May 2017 10:28:01 +0100
From:   John Garry <john.garry@...wei.com>
To:     wangyijing <wangyijing@...wei.com>,
        Dan Williams <dan.j.williams@...el.com>
CC:     "James E.J. Bottomley" <jejb@...ux.vnet.ibm.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        <chenqilin2@...wei.com>, <hare@...e.com>,
        linux-scsi <linux-scsi@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        <chenxiang66@...ilicon.com>, <huangdaode@...ilicon.com>,
        <wangkefeng.wang@...wei.com>, <zhaohongjiang@...wei.com>,
        <dingtianhong@...wei.com>, <guohanjun@...wei.com>,
        Wei Fang <fangwei1@...wei.com>, <yanaijie@...wei.com>,
        Christoph Hellwig <hch@....de>,
        Yousong He <heyousong@...wei.com>,
        Linuxarm <linuxarm@...wei.com>
Subject: Re: [PATCH 1/2] libsas: Don't process sas events in static works

On 22/05/2017 06:54, wangyijing wrote:
>> I also think for safety this should use a mempool that guarantees that
>> > events can continue to be processed under system memory pressure.
> What I am worried about is it's would still fail if the mempool is used empty during memory pressure.
>
>> > Also, have you considered the case when a broken phy starts throwing a
>> > constant stream of events? Is there a point at which libsas should
>> > stop queuing events and disable the phy?
> Not yet, I didn't find this issue in real case, but I agree, it's really a problem in some broken
> hardware, I think it's not a easy problem, we could improve it step by step.
>
> Thanks!
> Yijing.
>

I have seen this scenario on our development board when we have a bad 
physical cable connection - the PHY continually goes up and down in a loop.

So, in this regard, it is worth safeguarding against this scenario.

John