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From: "Ahmed S. Darwish" <a.darwish@linutronix.de>
To: John Garry <john.garry@huawei.com>
Cc: "James E.J. Bottomley" <jejb@linux.ibm.com>,
	"Martin K. Petersen" <martin.petersen@oracle.com>,
	Jason Yan <yanaijie@huawei.com>, Daniel Wagner <dwagner@suse.de>,
	Artur Paszkiewicz <artur.paszkiewicz@intel.com>,
	Jack Wang <jinpu.wang@cloud.ionos.com>,
	linux-scsi@vger.kernel.org, LKML <linux-kernel@vger.kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	"Sebastian A. Siewior" <bigeasy@linutronix.de>
Subject: Re: [PATCH v2 00/19] scsi: libsas: Remove in_interrupt() check
Date: Tue, 12 Jan 2021 18:33:06 +0100
Message-ID: <X/3dUkPCC1SrLT4m@lx-t490> (raw)
In-Reply-To: <e9bc0c89-a4d6-1e5b-793d-3c246882210e@huawei.com>

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.

Thanks,

--
Ahmed S. Darwish
Linutronix GmbH

  reply index

Thread overview: 37+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-01-12 11:06 Ahmed S. Darwish
2021-01-12 11:06 ` [PATCH v2 01/19] Documentation: scsi: libsas: Remove notify_ha_event() Ahmed S. Darwish
2021-01-12 11:06 ` [PATCH v2 02/19] scsi: libsas and users: Remove notifier indirection Ahmed S. Darwish
2021-01-12 11:36   ` John Garry
2021-01-12 12:09     ` Ahmed S. Darwish
2021-01-12 13:07     ` [PATCH v3 " Ahmed S. Darwish
2021-01-12 15:43       ` Christoph Hellwig
2021-01-12 11:06 ` [PATCH v2 03/19] scsi: libsas: Introduce a _gfp() variant of event notifiers Ahmed S. Darwish
2021-01-12 15:45   ` Christoph Hellwig
2021-01-12 17:12     ` Sebastian A. Siewior
2021-01-12 11:06 ` [PATCH v2 04/19] scsi: mvsas: Pass gfp_t flags to libsas " Ahmed S. Darwish
2021-01-12 15:46   ` Christoph Hellwig
2021-01-12 17:03     ` Ahmed S. Darwish
2021-01-12 11:06 ` [PATCH v2 05/19] scsi: isci: port: link down: Pass gfp_t flags Ahmed S. Darwish
2021-01-12 11:06 ` [PATCH v2 06/19] scsi: isci: port: link up: " Ahmed S. Darwish
2021-01-12 11:06 ` [PATCH v2 07/19] scsi: isci: port: broadcast change: " Ahmed S. Darwish
2021-01-12 11:06 ` [PATCH v2 08/19] scsi: libsas: Pass gfp_t flags to event notifiers Ahmed S. Darwish
2021-01-12 11:06 ` [PATCH v2 09/19] scsi: pm80xx: Pass gfp_t flags to libsas " Ahmed S. Darwish
2021-01-12 11:06 ` [PATCH v2 10/19] scsi: aic94xx: " Ahmed S. Darwish
2021-01-12 11:06 ` [PATCH v2 11/19] scsi: hisi_sas: " Ahmed S. Darwish
2021-01-12 11:06 ` [PATCH v2 12/19] scsi: libsas: event notifiers API: Add gfp_t flags parameter Ahmed S. Darwish
2021-01-12 11:06 ` [PATCH v2 13/19] scsi: hisi_sas: Switch back to original libsas event notifiers Ahmed S. Darwish
2021-01-12 11:06 ` [PATCH v2 14/19] scsi: aic94xx: " Ahmed S. Darwish
2021-01-12 11:06 ` [PATCH v2 15/19] scsi: pm80xx: " Ahmed S. Darwish
2021-01-12 11:06 ` [PATCH v2 16/19] scsi: libsas: Switch back to original event notifiers API Ahmed S. Darwish
2021-01-12 14:42   ` John Garry
2021-01-12 11:06 ` [PATCH v2 17/19] scsi: isci: Switch back to original libsas event notifiers Ahmed S. Darwish
2021-01-12 11:06 ` [PATCH v2 18/19] scsi: mvsas: " Ahmed S. Darwish
2021-01-12 11:06 ` [PATCH v2 19/19] scsi: libsas: Remove temporarily-added _gfp() API variants Ahmed S. Darwish
2021-01-12 11:53 ` [PATCH v2 00/19] scsi: libsas: Remove in_interrupt() check John Garry
2021-01-12 13:19   ` Ahmed S. Darwish
2021-01-12 16:00     ` John Garry
2021-01-12 17:33       ` Ahmed S. Darwish [this message]
2021-01-14  9:51         ` John Garry
2021-01-15 16:27           ` Ahmed S. Darwish
2021-01-15 16:29             ` John Garry
2021-01-15 16:41               ` Ahmed S. Darwish

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