linux-kernel - Re: [PATCH v2] scsi: libsas: Reset num_scatter if libata mark qc as NODATA

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Message-ID: <CABGCNpBABSkdSQf=c2T9qMTGgJPL7Si9Ft_DvC8WiLtT_vmL1Q@mail.gmail.com>
Date:   Thu, 1 Apr 2021 15:34:58 -0700
From:   Jolly Shah <jollys@...gle.com>
To:     luojiaxing <luojiaxing@...wei.com>
Cc:     John Garry <john.garry@...wei.com>,
        Jason Yan <yanaijie@...wei.com>, jejb@...ux.ibm.com,
        martin.petersen@...cle.com, a.darwish@...utronix.de,
        dan.carpenter@...cle.com, b.zolnierkie@...sung.com,
        linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] scsi: libsas: Reset num_scatter if libata mark qc as NODATA

Hi Luojiaxing,


On Mon, Mar 22, 2021 at 1:41 AM luojiaxing <luojiaxing@...wei.com> wrote:
>
>
> On 2021/3/20 20:14, John Garry wrote:
> > On 19/03/2021 01:43, Jason Yan wrote:
> >>
> >>
> >> 在 2021/3/19 6:56, Jolly Shah 写道:
> >>> When the cache_type for the scsi device is changed, the scsi layer
> >>> issues a MODE_SELECT command. The caching mode details are communicated
> >>> via a request buffer associated with the scsi command with data
> >>> direction set as DMA_TO_DEVICE (scsi_mode_select). When this command
> >>> reaches the libata layer, as a part of generic initial setup, libata
> >>> layer sets up the scatterlist for the command using the scsi command
> >>> (ata_scsi_qc_new). This command is then translated by the libata layer
> >>> into ATA_CMD_SET_FEATURES (ata_scsi_mode_select_xlat). The libata layer
> >>> treats this as a non data command (ata_mselect_caching), since it only
> >>> needs an ata taskfile to pass the caching on/off information to the
> >>> device. It does not need the scatterlist that has been setup, so it
> >>> does
> >>> not perform dma_map_sg on the scatterlist (ata_qc_issue).
> >>> Unfortunately,
> >>> when this command reaches the libsas layer(sas_ata_qc_issue), libsas
> >>> layer sees it as a non data command with a scatterlist. It cannot
> >>> extract the correct dma length, since the scatterlist has not been
> >>> mapped with dma_map_sg for a DMA operation. When this partially
> >>> constructed SAS task reaches pm80xx LLDD, it results in below warning.
> >>>
> >>> "pm80xx_chip_sata_req 6058: The sg list address
> >>> start_addr=0x0000000000000000 data_len=0x0end_addr_high=0xffffffff
> >>> end_addr_low=0xffffffff has crossed 4G boundary"
> >>>
> >>> This patch updates code to handle ata non data commands separately so
> >>> num_scatter and total_xfer_len remain 0.
> >>>
> >>> Fixes: 53de092f47ff ("scsi: libsas: Set data_dir as DMA_NONE if
> >>> libata marks qc as NODATA")
> >>> Signed-off-by: Jolly Shah <jollys@...gle.com>
> >
> > Reviewed-by: John Garry <john.garry@...wei.com>
> >
> > @luojiaxing, can you please test this?
>
>
> Sure, let me take a look, and reply the test result here later
>

Wanted to follow up on test results. Any updates?

Thanks,
Jolly

>
> Thanks
>
> Jiaxing
>
>
> >
> >>> ---
> >>> v2:
> >>> - reorganized code to avoid setting num_scatter twice
> >>>
> >>>   drivers/scsi/libsas/sas_ata.c | 9 ++++-----
> >>>   1 file changed, 4 insertions(+), 5 deletions(-)
> >>>
> >>> diff --git a/drivers/scsi/libsas/sas_ata.c
> >>> b/drivers/scsi/libsas/sas_ata.c
> >>> index 024e5a550759..8b9a39077dba 100644
> >>> --- a/drivers/scsi/libsas/sas_ata.c
> >>> +++ b/drivers/scsi/libsas/sas_ata.c
> >>> @@ -201,18 +201,17 @@ static unsigned int sas_ata_qc_issue(struct
> >>> ata_queued_cmd *qc)
> >>>           memcpy(task->ata_task.atapi_packet, qc->cdb,
> >>> qc->dev->cdb_len);
> >>>           task->total_xfer_len = qc->nbytes;
> >>>           task->num_scatter = qc->n_elem;
> >>> +        task->data_dir = qc->dma_dir;
> >>> +    } else if (qc->tf.protocol == ATA_PROT_NODATA) {
> >>> +        task->data_dir = DMA_NONE;
> >>
> >> Hi Jolly & John,
> >>
> >> We only set DMA_NONE for ATA_PROT_NODATA, I'm curious about why
> >> ATA_PROT_NCQ_NODATA and ATAPI_PROT_NODATA do not need to set DMA_NONE?
> >
> > So we can see something like atapi_eh_tur() -> ata_exec_internal(),
> > which is a ATAPI NONDATA and has DMA_NONE, so should be ok.
> >
> > Other cases, like those using the xlate function on the qc for
> > ATA_PROT_NCQ_NODATA, could be checked further.
> >
> > For now, we're just trying to fix the fix.
> >
> >>
> >> Thanks,
> >> Jason
> >>
> >>
> >>>       } else {
> >>>           for_each_sg(qc->sg, sg, qc->n_elem, si)
> >>>               xfer += sg_dma_len(sg);
> >>>           task->total_xfer_len = xfer;
> >>>           task->num_scatter = si;
> >>> -    }
> >>> -
> >>> -    if (qc->tf.protocol == ATA_PROT_NODATA)
> >>> -        task->data_dir = DMA_NONE;
> >>> -    else
> >>>           task->data_dir = qc->dma_dir;
> >>> +    }
> >>>       task->scatter = qc->sg;
> >>>       task->ata_task.retry_count = 1;
> >>>       task->task_state_flags = SAS_TASK_STATE_PENDING;
> >>>
> >> .
> >
> >
> > .
> >
>