linux-kernel - Re: [PATCH v2 00/19] scsi: libsas: Remove in

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Date:   Thu, 14 Jan 2021 09:51:35 +0000
From:   John Garry <john.garry@...wei.com>
To:     "Ahmed S. Darwish" <a.darwish@...utronix.de>
CC:     "James E.J. Bottomley" <jejb@...ux.ibm.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        Jason Yan <yanaijie@...wei.com>,
        Daniel Wagner <dwagner@...e.de>,
        Artur Paszkiewicz <artur.paszkiewicz@...el.com>,
        Jack Wang <jinpu.wang@...ud.ionos.com>,
        <linux-scsi@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Sebastian A. Siewior" <bigeasy@...utronix.de>
Subject: Re: [PATCH v2 00/19] scsi: libsas: Remove in_interrupt() check

On 12/01/2021 17:33, Ahmed S. Darwish wrote:
> On Tue, Jan 12, 2021 at 04:00:57PM +0000, John Garry wrote:
> ...
>> I boot-tested on my machines which have hisi_sas v2 and v3 hw, and it's ok.
>> I will ask some guys to test a bit more.
>>
> Thanks a lot!
> 
>> And generally the changes look ok. But I just have a slight concern that we
>> don't pass the gfp_flags all the way from the origin caller.
>>
>> So we have some really long callchains, for example:
>>
>> host.c: sci_controller_error_handler(): atomic, irq handler     (*)
>> OR host.c: sci_controller_completion_handler(), atomic, tasklet (*)
>>    -> sci_controller_process_completions()
>>      -> sci_controller_unsolicited_frame()
>>        -> phy.c: sci_phy_frame_handler()
>>          -> sci_change_state(SCI_PHY_SUB_AWAIT_SAS_POWER)
>>            -> sci_phy_starting_await_sas_power_substate_enter()
>>              -> host.c: sci_controller_power_control_queue_insert()
>>                -> phy.c: sci_phy_consume_power_handler()
>>                  -> sci_change_state(SCI_PHY_SUB_FINAL)
>>          -> sci_change_state(SCI_PHY_SUB_FINAL)
>>      -> sci_controller_event_completion()
>>        -> phy.c: sci_phy_event_handler()
>>          -> sci_phy_start_sata_link_training()
>>            -> sci_change_state(SCI_PHY_SUB_AWAIT_SATA_POWER)
>>              -> sci_phy_starting_await_sata_power_substate_enter
>>                -> host.c: sci_controller_power_control_queue_insert()
>>                  -> phy.c: sci_phy_consume_power_handler()
>>                    -> sci_change_state(SCI_PHY_SUB_FINAL)
>>
>> So if someone rearranges the code later, adds new callchains, etc., it could
>> be missed that the context may have changed than what we assume at the
>> bottom. But then passing the flags everywhere is cumbersome, and all the
>> libsas users see little or no significant changes anyway, apart from a
>> couple.
>>
> The deep call chains like the one you've quoted are all within the isci
> Intel driver (patches #5 => #7), due to the*massive*  state transitions
> that driver has. But as the commit logs of these three patches show,
> almost all of such transitions happened under atomic context anyway and
> GFP_ATOMIC was thus used.
> 
> The GFP_KERNEL call-chains were all very simple: a workqueue, functions
> already calling msleep() or wait_event_timeout() two or three lines
> nearby, and so on.
> 
> All the other libsas clients (that is, except isci) also had normal call
> chains that were IMHO easy to follow.

To me, the series looks fine. Well, the end result - I didn't go through 
patch by patch. So:

Reviewed-by: John Garry <john.garry@...wei.com>

I'm still hoping some guys are testing a bit for me, but I'll let you 
know if any problem.

As an aside, your analysis showed some quite poor usage of spinlocks in 
some drivers, specifically grabbing a lock and then calling into a depth 
of 3 or 4 functions.

Thanks,
John