linux-kernel - Re: [PATCH V2] scsi: libsas: Directly kick-off EH when ATA device fell off

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Date:   Mon, 19 Dec 2022 09:23:03 +0000
From:   John Garry <john.g.garry@...cle.com>
To:     Xingui Yang <yangxingui@...wei.com>, jejb@...ux.ibm.com,
        martin.petersen@...cle.com, damien.lemoal@...nsource.wdc.com,
        linux-ide@...r.kernel.org, hare@...e.com, hch@....de
Cc:     linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org,
        linuxarm@...wei.com, prime.zeng@...ilicon.com,
        kangfenglong@...wei.com
Subject: Re: [PATCH V2] scsi: libsas: Directly kick-off EH when ATA device
 fell off

On 16/12/2022 10:03, Xingui Yang wrote:
> If the ATA device fell off, call sas_ata_device_link_abort() directly and
> mark all outstanding QCs as failed and kick-off EH Immediately. This avoids
> having to wait for block layer timeouts.
> 
> Signed-off-by: Xingui Yang <yangxingui@...wei.com>
> ---
> Changes to v1:
> - Use dev_is_sata() to check ATA device type
>   drivers/scsi/libsas/sas_discover.c | 3 +++
>   1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/scsi/libsas/sas_discover.c b/drivers/scsi/libsas/sas_discover.c
> index d5bc1314c341..a12b65eb4a2a 100644
> --- a/drivers/scsi/libsas/sas_discover.c
> +++ b/drivers/scsi/libsas/sas_discover.c
> @@ -362,6 +362,9 @@ static void sas_destruct_ports(struct asd_sas_port *port)
>   
>   void sas_unregister_dev(struct asd_sas_port *port, struct domain_device *dev)
>   {
> +	if (test_bit(SAS_DEV_GONE, &dev->state) && dev_is_sata(dev))
> +		sas_ata_device_link_abort(dev, false);

Firstly, I think that there is a bug in sas_ata_device_link_abort() -> 
ata_link_abort() code in that the host lock in not grabbed, as the 
comment in ata_port_abort() mentions. Having said that, libsas had 
already some dodgy host locking usage - specifically dropping the lock 
for the queuing path (that's something else to be fixed up ... I think 
that is due to queue command CB calling task_done() in some cases), but 
I still think that sas_ata_device_link_abort() should be fixed (to grab 
the host lock).

Secondly, this just seems like a half solution to the age-old problem - 
that is, EH eventually kicking in only after 30 seconds when a disk is 
removed with active IO. I say half solution as SAS disks still have this 
issue for libsas. Can we instead push to try to solve both of them now?

There was a broad previous discussion on this:
https://urldefense.com/v3/__https://lore.kernel.org/linux-scsi/Ykqg0kr0F*2Fyzk2XW@infradead.org/__;JQ!!ACWV5N9M2RV99hQ!MwAZFXXIwuP0lv-kuUIJ0ekUiGBWlTBhU3oQjyOf_yuP1rHDJb8UKMzJjndXNQ-W1PQGJXzgc0bQUsHh4NGh21EOc50$

 From that discussion, Hannes was doing some related prep work series, 
but I don't think it got completed.

Thanks,
John

> +
>   	if (!test_bit(SAS_DEV_DESTROY, &dev->state) &&
>   	    !list_empty(&dev->disco_list_node)) {
>   		/* this rphy never saw sas_rphy_add */