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

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Date:   Mon, 22 May 2017 13:54:30 +0800
From:   wangyijing <wangyijing@...wei.com>
To:     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>,
        John Garry <john.garry@...wei.com>,
        Wei Fang <fangwei1@...wei.com>, <yanaijie@...wei.com>,
        Christoph Hellwig <hch@....de>,
        Yousong He <heyousong@...wei.com>
Subject: Re: [PATCH 1/2] libsas: Don't process sas events in static works

Hi Dan, thanks for your review and comments!

在 2017/5/21 11:44, Dan Williams 写道:
> On Fri, May 19, 2017 at 11:39 PM, Yijing Wang <wangyijing@...wei.com> wrote:
>> Now libsas hotplug work is static, LLDD driver queue
>> the hotplug work into shost->work_q. If LLDD driver
>> burst post lots hotplug events to libsas, the hotplug
>> events may pending in the workqueue like
>>
>> shost->work_q
>> new work[PORTE_BYTES_DMAED] --> |[PHYE_LOSS_OF_SIGNAL][PORTE_BYTES_DMAED] -> processing
>>                                 |<-------wait worker to process-------->|
>> In this case, a new PORTE_BYTES_DMAED event coming, libsas try to queue it
>> to shost->work_q, but this work is already pending, so it would be lost.
>> Finally, libsas delete the related sas port and sas devices, but LLDD driver
>> expect libsas add the sas port and devices(last sas event).
>>
>> This patch remove the static defined hotplug work, and use dynamic work to
>> avoid missing hotplug events.
> 
> If we go this route we don't even need:
> 
> sas_port_event_fns
> sas_phy_event_fns
> sas_ha_event_fns

Yes, these three fns are not necessary, just for avoid lots kfree in phy/port/ha event fns.

> 
> ...just specify the target routine directly to INIT_WORK() and remove
> the indirection.
> 
> 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.

> 
> .
>