linux-kernel - Re: [PATCH v2 1/2] libsas: Don't process sas events in static works

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Date:   Wed, 14 Jun 2017 14:08:16 +0100
From:   John Garry <john.garry@...wei.com>
To:     wangyijing <wangyijing@...wei.com>,
        Johannes Thumshirn <jthumshirn@...e.de>,
        <jejb@...ux.vnet.ibm.com>, <martin.petersen@...cle.com>
CC:     <chenqilin2@...wei.com>, <hare@...e.com>,
        <linux-scsi@...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>,
        <yanaijie@...wei.com>, <hch@....de>, <dan.j.williams@...el.com>,
        <emilne@...hat.com>, <thenzl@...hat.com>, <wefu@...hat.com>,
        <charles.chenxin@...wei.com>, <chenweilong@...wei.com>,
        Yousong He <heyousong@...wei.com>
Subject: Re: [PATCH v2 1/2] libsas: Don't process sas events in static works

On 14/06/2017 10:04, wangyijing wrote:
>>>  static void notify_ha_event(struct sas_ha_struct *sas_ha, enum ha_event event)
>>> >>  {
>>> >> +	struct sas_ha_event *ev;
>>> >> +
>>> >>  	BUG_ON(event >= HA_NUM_EVENTS);
>>> >>
>>> >> -	sas_queue_event(event, &sas_ha->pending,
>>> >> -			&sas_ha->ha_events[event].work, sas_ha);
>>> >> +	ev = kzalloc(sizeof(*ev), GFP_ATOMIC);
>>> >> +	if (!ev)
>>> >> +		return;
>> > GFP_ATOMIC allocations can fail and then no events will be queued *and* we
>> > don't report the error back to the caller.
>> >
> Yes, it's really a problem, but I don't find a better solution, do you have some suggestion ?
>

Dan raised an issue with this approach, regarding a malfunctioning PHY 
which spews out events. I still don't think we're handling it safely. 
Here's the suggestion:
- each asd_sas_phy owns a finite-sized pool of events
- when the event pool becomes exhausted, libsas stops queuing events 
(obviously) and disables the PHY in the LLDD
- upon attempting to re-enable the PHY from sysfs, libsas first checks 
that the pool is still not exhausted

If you cannot find a good solution, then let us know and we can help.

John