Re: [PATCH] ata: libata: Set DID_TIME_OUT for commands that actually timed out

[Damien Le Moal <dlemoal@kernel.org>]

On 10/23/24 19:55, Niklas Cassel wrote:
> When ata_qc_complete() schedules a command for EH using
> ata_qc_schedule_eh(), blk_abort_request() will be called, which leads to
> req->q->mq_ops->timeout() / scsi_timeout() being called.
> 
> scsi_timeout(), if the LLDD has no abort handler (libata has no abort
> handler), will set host byte to DID_TIME_OUT, and then call
> scsi_eh_scmd_add() to add the command to EH.
> 
> Thus, when commands first enter libata's EH strategy_handler, all the
> commands that have been added to EH will have DID_TIME_OUT set.
> 
> Commit e5dd410acb34 ("ata: libata: Clear DID_TIME_OUT for ATA PT commands
> with sense data") clears this bogus DID_TIME_OUT flag for all commands
> that reached libata's EH strategy_handler.
> 
> libata has its own flag (AC_ERR_TIMEOUT), that it sets for commands that
> have not received a completion at the time of entering EH.
> 
> ata_eh_worth_retry() has no special handling for AC_ERR_TIMEOUT, so by
> default timed out commands will get flag ATA_QCFLAG_RETRY set and will be
> retried after the port has been reset (ata_eh_link_autopsy() always
> triggers a port reset if any command has AC_ERR_TIMEOUT set).
> 
> For commands that have ATA_QCFLAG_RETRY set, but also has an error flag
> set (e.g. AC_ERR_TIMEOUT), ata_eh_finish() will not increment
> scmd->allowed, so the command will at most be retried (scmd->allowed
> number of times, which by default is set to 3).
> 
> However, scsi_eh_flush_done_q() will only retry commands for which
> scsi_noretry_cmd() returns false.
> 
> For commands that has DID_TIME_OUT set, if the command is either
> has FAILFAST or if the command is a passthrough command, scsi_noretry_cmd()
> will return true. Thus, such commands will never be retried.
> 
> Thus, make sure that libata sets SCSI's DID_TIME_OUT flag for commands that
> actually timed out (libata's AC_ERR_TIMEOUT flag), such that timed out
> commands will once again not be retried if they are also a FAILFAST or
> passthrough command.
> 
> Cc: stable@vger.kernel.org
> Fixes: e5dd410acb34 ("ata: libata: Clear DID_TIME_OUT for ATA PT commands with sense data")
> Reported-by: Lai, Yi <yi1.lai@linux.intel.com>
> Closes: https://lore.kernel.org/linux-ide/ZxYz871I3Blsi30F@ly-workstation/
> Signed-off-by: Niklas Cassel <cassel@kernel.org>

Looks good.

Reviewed-by: Damien Le Moal <dlemoal@kernel.org>

> ---
>  drivers/ata/libata-eh.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/ata/libata-eh.c b/drivers/ata/libata-eh.c
> index fa41ea57a978..3b303d4ae37a 100644
> --- a/drivers/ata/libata-eh.c
> +++ b/drivers/ata/libata-eh.c
> @@ -651,6 +651,7 @@ void ata_scsi_cmd_error_handler(struct Scsi_Host *host, struct ata_port *ap,
>  			/* the scmd has an associated qc */
>  			if (!(qc->flags & ATA_QCFLAG_EH)) {
>  				/* which hasn't failed yet, timeout */
> +				set_host_byte(scmd, DID_TIME_OUT);
>  				qc->err_mask |= AC_ERR_TIMEOUT;
>  				qc->flags |= ATA_QCFLAG_EH;
>  				nr_timedout++;


-- 
Damien Le Moal
Western Digital Research