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Message-ID: <8280ec1c-c274-ba8d-b533-3316865fe5c1@huawei.com>
Date:   Thu, 27 Oct 2022 11:45:08 +0100
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Subject: Re: [PATCH RFC v3 1/7] ata: libata-scsi: Add
 ata_scsi_queue_internal()
To:     Damien Le Moal <damien.lemoal@opensource.wdc.com>,
        <jejb@linux.ibm.com>, <martin.petersen@oracle.com>, <hare@suse.de>,
        <bvanassche@acm.org>, <hch@lst.de>, <ming.lei@redhat.com>,
        <niklas.cassel@wdc.com>
CC:     <axboe@kernel.dk>, <jinpu.wang@cloud.ionos.com>,
        <linux-block@vger.kernel.org>, <linux-kernel@vger.kernel.org>,
        <linux-ide@vger.kernel.org>, <linux-scsi@vger.kernel.org>,
        <linuxarm@huawei.com>
References: <1666693976-181094-1-git-send-email-john.garry@huawei.com>
 <1666693976-181094-2-git-send-email-john.garry@huawei.com>
 <8ed42281-4400-a0ed-92f1-c57b9de726a4@opensource.wdc.com>
From:   John Garry <john.garry@huawei.com>
In-Reply-To: <8ed42281-4400-a0ed-92f1-c57b9de726a4@opensource.wdc.com>
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On 27/10/2022 02:42, Damien Le Moal wrote:
> On 10/25/22 19:32, John Garry wrote:
>> Add a function to handle queued ATA internal SCSI cmnds - does much the
>> same as ata_exec_internal_sg() does (which will be fixed up later to
>> actually queue internal cmnds through this function).
>>
>> Signed-off-by: John Garry <john.garry@huawei.com>
>> ---
>>   drivers/ata/libata-sata.c |  3 +++
>>   drivers/ata/libata-scsi.c | 43 +++++++++++++++++++++++++++++++++++++++
>>   drivers/ata/libata.h      |  3 ++-
>>   include/linux/libata.h    |  6 ++++++
>>   4 files changed, 54 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/ata/libata-sata.c b/drivers/ata/libata-sata.c
>> index b6806d41a8c5..e8b828c56542 100644
>> --- a/drivers/ata/libata-sata.c
>> +++ b/drivers/ata/libata-sata.c
>> @@ -1258,6 +1258,9 @@ int ata_sas_queuecmd(struct scsi_cmnd *cmd, struct ata_port *ap)
>>   {
>>   	int rc = 0;
>>   
>> +	if (blk_mq_is_reserved_rq(scsi_cmd_to_rq(cmd)))
>> +		return ata_scsi_queue_internal(cmd, ap->link.device);
>> +
>>   	if (likely(ata_dev_enabled(ap->link.device)))
>>   		rc = __ata_scsi_queuecmd(cmd, ap->link.device);
>>   	else {
>> diff --git a/drivers/ata/libata-scsi.c b/drivers/ata/libata-scsi.c
>> index 476e0ef4bd29..30d7c90b0c35 100644
>> --- a/drivers/ata/libata-scsi.c
>> +++ b/drivers/ata/libata-scsi.c
>> @@ -3965,6 +3965,49 @@ static inline ata_xlat_func_t ata_get_xlat_func(struct ata_device *dev, u8 cmd)
>>   	return NULL;
>>   }
>>   
>> +unsigned int ata_scsi_queue_internal(struct scsi_cmnd *scmd,
>> +				     struct ata_device *dev)
>> +{
>> +	struct ata_link *link = dev->link;
>> +	struct ata_port *ap = link->ap;
>> +	struct ata_queued_cmd *qc;
>> +
>> +	/* no internal command while frozen */
>> +	if (ap->pflags & ATA_PFLAG_FROZEN)
>> +		goto did_err;
>> +
>> +	/* initialize internal qc */
>> +	qc = __ata_qc_from_tag(ap, ATA_TAG_INTERNAL);
>> +	link->preempted_tag = link->active_tag;
>> +	link->preempted_sactive = link->sactive;
>> +	ap->preempted_qc_active = ap->qc_active;
>> +	ap->preempted_nr_active_links = ap->nr_active_links;
>> +	link->active_tag = ATA_TAG_POISON;
>> +	link->sactive = 0;
>> +	ap->qc_active = 0;
>> +	ap->nr_active_links = 0;
>> +
>> +	if (qc->dma_dir != DMA_NONE) {
>> +		int n_elem;
>> +
>> +		n_elem = 1;
>> +		qc->n_elem = n_elem;
>> +		qc->sg = scsi_sglist(scmd);
>> +		qc->nbytes = qc->sg->length;
>> +		ata_sg_init(qc, qc->sg, n_elem);
>> +	}
>> +
>> +	scmd->submitter = SUBMITTED_BY_BLOCK_LAYER;
>> +
>> +	ata_qc_issue(qc);
> 
> Arg, no ! This potentially mixes NCQ and non-NCQ commands, which is
> forbidden by ATA spec. You need to use something like:
> 
> 	if (ap->ops->qc_defer) {
> 		if ((rc = ap->ops->qc_defer(qc)))
> 			goto defer;
> 	}
> 
> 	ata_qc_issue(qc);
> 
> which is done in __ata_scsi_queuecmd() -> ata_scsi_translate()
> 
> Unless you guarantee that ata_scsi_queue_internal() is always called
> from libata EH context ?

This will be called synchronously called from ata_exec_internal_sg(), so 
the same rules on NCQ vs non-NCQ would apply here. As I see, 
ata_exec_internal_sg() assumes non-NCQ mode and is not multi-thread safe.

Thanks,
John

> 
>> +
>> +	return 0;
>> +did_err:
>> +	scmd->result = (DID_ERROR << 16);
>> +	scsi_done(scmd);
>> +	return 0;
>> +}
>> +
>>   int __ata_scsi_queuecmd(struct scsi_cmnd *scmd, struct ata_device *dev)
>>   {
>>   	u8 scsi_op = scmd->cmnd[0];
>> diff --git a/drivers/ata/libata.h b/drivers/ata/libata.h
>> index 0c2df1e60768..15cd1cd618b8 100644
>> --- a/drivers/ata/libata.h
>> +++ b/drivers/ata/libata.h
>> @@ -82,7 +82,6 @@ extern int ata_port_probe(struct ata_port *ap);
>>   extern void __ata_port_probe(struct ata_port *ap);
>>   extern unsigned int ata_read_log_page(struct ata_device *dev, u8 log,
>>   				      u8 page, void *buf, unsigned int sectors);
>> -
>>   #define to_ata_port(d) container_of(d, struct ata_port, tdev)
>>   
>>   /* libata-acpi.c */
>> @@ -130,6 +129,8 @@ extern int ata_scsi_user_scan(struct Scsi_Host *shost, unsigned int channel,
>>   void ata_scsi_sdev_config(struct scsi_device *sdev);
>>   int ata_scsi_dev_config(struct scsi_device *sdev, struct ata_device *dev);
>>   int __ata_scsi_queuecmd(struct scsi_cmnd *scmd, struct ata_device *dev);
>> +unsigned int ata_scsi_queue_internal(struct scsi_cmnd *scmd,
>> +				     struct ata_device *dev);
>>   
>>   /* libata-eh.c */
>>   extern unsigned int ata_internal_cmd_timeout(struct ata_device *dev, u8 cmd);
>> diff --git a/include/linux/libata.h b/include/linux/libata.h
>> index 827d5838cd23..8938b584520f 100644
>> --- a/include/linux/libata.h
>> +++ b/include/linux/libata.h
>> @@ -764,7 +764,9 @@ struct ata_link {
>>   
>>   	struct device		tdev;
>>   	unsigned int		active_tag;	/* active tag on this link */
>> +	unsigned int		preempted_tag;
>>   	u32			sactive;	/* active NCQ commands */
>> +	u32			preempted_sactive;
>>   
>>   	unsigned int		flags;		/* ATA_LFLAG_xxx */
>>   
>> @@ -857,6 +859,10 @@ struct ata_port {
>>   #ifdef CONFIG_ATA_ACPI
>>   	struct ata_acpi_gtm	__acpi_init_gtm; /* use ata_acpi_init_gtm() */
>>   #endif
>> +
>> +	u64 preempted_qc_active;
>> +	int preempted_nr_active_links;
>> +
>>   	/* owned by EH */
>>   	u8			sector_buf[ATA_SECT_SIZE] ____cacheline_aligned;
>>   };
>