Re: [PATCH v2] ata: libata-core: do not issue non-internal commands once EH is pending

Niklas Cassel
2022-11-09T09:28:28Z

On Wed, Nov 09, 2022 at 08:11:17AM +0100, Hannes Reinecke wrote:
> Thanks for the detailed explanation, Niklas.
>
> However, one fundamental thing is still unresolved:
> I've switched SCSI EH to do asynchronous aborts with commit e494f6a72839
> ("[SCSI] improved eh timeout handler"); since then commands will be aborted
> without invoking SCSI EH.
>
> This goes _fundamentally_ against libata's .eh_strategy (as it's never
> invoked), and as such libata _cannot_ use command aborts.
> Which typically wouldn't matter as ATA doesn't have command aborts, and
> realistically any error is causing the NCQ queue to be drained.
>
> So SCSI EH scsi_abort_command() really shouldn't queue a workqueue item, as
> it'll never be able to do anything meaningful.
>
> You need this patch:
>
> diff --git a/drivers/scsi/scsi_error.c b/drivers/scsi/scsi_error.c
> index be2a70c5ac6d..4fb72b73871e 100644
> --- a/drivers/scsi/scsi_error.c
> +++ b/drivers/scsi/scsi_error.c
> @@ -242,6 +242,11 @@ scsi_abort_command(struct scsi_cmnd *scmd)
> return FAILED;
> }
>
> + if (!hostt->eh_abort_handler) {
> + /* No abort handler, fail command directly */
> + return FAILED;
> + }
> +
> spin_lock_irqsave(shost->host_lock, flags);
> if (shost->eh_deadline != -1 && !shost->last_reset)
> shost->last_reset = jiffies;
>
> to avoid having libata trying to queue a (pointless) abort workqueue item,
> and get rid of the various workqueue thingies you mentioned above.
>
> And it's a sensible fix anyway, will be sending it as a separate patch.

Hello Hannes,

This is how it looks before your patch:
scsi_logging_level -s -E 7

[ 33.737069] sd 0:0:0:0: [sda] tag#0 abort scheduled
[ 33.738812] sd 0:0:0:0: [sda] tag#3 abort scheduled
[ 33.749085] sd 0:0:0:0: [sda] tag#0 aborting command
[ 33.751393] sd 0:0:0:0: [sda] tag#0 cmd abort failed
[ 33.753541] sd 0:0:0:0: [sda] tag#3 aborting command
[ 33.755565] sd 0:0:0:0: [sda] tag#3 cmd abort failed
[ 33.763051] scsi host0: Waking error handler thread
[ 33.765727] scsi host0: scsi_eh_0: waking up 0/2/2
[ 33.768815] ata1.00: exception Emask 0x0 SAct 0x9 SErr 0x0 action 0x0
[ 33.772211] ata1.00: irq_stat 0x40000000
[ 33.774187] ata1.00: failed command: WRITE FPDMA QUEUED
[ 33.776962] ata1.00: cmd 61/00:00:00:00:0f/01:00:00:00:00/40 tag 0 ncq dma 131072 out
[ 33.776962] res 43/04:00:00:00:00/00:00:00:00:00/00 Emask 0x400 (NCQ error) <F>
[ 33.783598] ata1.00: status: { DRDY SENSE ERR }
[ 33.785252] ata1.00: error: { ABRT }
[ 33.791290] ata1.00: configured for UDMA/100
[ 33.792195] sd 0:0:0:0: [sda] tag#0 scsi_eh_0: flush finish cmd
[ 33.793426] sd 0:0:0:0: [sda] tag#3 scsi_eh_0: flush finish cmd
[ 33.794653] ata1: EH complete

So we do get the scmd:s sent to ATA EH (strategy_handler).

In scmd_eh_abort_handler(), scsi_try_to_abort_cmd() will return FAILED
since hostt->eh_abort_handler is not implemented for libata, so
scmd_eh_abort_handler() will do goto out; which calls scsi_eh_scmd_add().

This is how it looks after your patch:
scsi_logging_level -s -E 7

[ 223.417749] scsi host0: Waking error handler thread
[ 223.419782] scsi host0: scsi_eh_0: waking up 0/2/2
[ 223.423101] ata1.00: exception Emask 0x0 SAct 0x80002 SErr 0x0 action 0x0
[ 223.425362] ata1.00: irq_stat 0x40000008
[ 223.426778] ata1.00: failed command: WRITE FPDMA QUEUED
[ 223.428925] ata1.00: cmd 61/00:08:00:00:0f/01:00:00:00:00/40 tag 1 ncq dma 131072 out
[ 223.428925] res 43/04:00:00:00:00/00:00:00:00:00/00 Emask 0x400 (NCQ error) <F>
[ 223.436077] ata1.00: status: { DRDY SENSE ERR }
[ 223.438015] ata1.00: error: { ABRT }
[ 223.441179] ata1.00: Security Log not supported
[ 223.445698] ata1.00: Security Log not supported
[ 223.448475] ata1.00: configured for UDMA/100
[ 223.449790] sd 0:0:0:0: [sda] tag#1 scsi_eh_0: flush finish cmd
[ 223.451063] sd 0:0:0:0: [sda] tag#19 scsi_eh_0: flush finish cmd
[ 223.452648] ata1: EH complete

So your patch looks good to me, like you said, it removes a
a pointless queue_work().

Do we perhaps want to remove the !hostt->eh_abort_handler check
from scmd_eh_abort_handler(), now when you've moved it earlier
(to scsi_abort_command()) ? Perhaps we need to keep it, since
the function used for checking this, scsi_try_to_abort_cmd()
is used in other places as well.

Kind regards,
Niklas