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SubjectRe: [PATCH v3] sd: Ignore sync cache failures when not supported
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On Tue, 2017-05-09 at 17:43 +0200, Thierry Escande wrote:
> From: Derek Basehore <dbasehore@chromium.org>
>
> Some external hard drives don't support the sync command even though the
> hard drive has write cache enabled. In this case, upon suspend request,
> sync cache failures are ignored if the error code in the sense header is
> ILLEGAL_REQUEST. There's not much we can do for these drives, so we
> shouldn't fail to suspend for this error case. The drive may stay
> powered if that's the setup for the port it's plugged into.
>
> Signed-off-by: Derek Basehore <dbasehore@chromium.org>
> Signed-off-by: Thierry Escande <thierry.escande@collabora.com>
> ---
>
> v3 changes:
> - Pass the sense_hdr structure to sd_sync_cache() instead of the
> lonely sense_key field
>
> v2 changes:
> - Change sense_key type to u8 in sd_sync_cache()
>
> drivers/scsi/sd.c | 34 +++++++++++++++++++++++++---------
> 1 file changed, 25 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c
> index fcfeddc..ee69fee 100644
> --- a/drivers/scsi/sd.c
> +++ b/drivers/scsi/sd.c
> @@ -1489,17 +1489,21 @@ static unsigned int sd_check_events(struct gendisk *disk, unsigned int clearing)
> return retval;
> }
>
> -static int sd_sync_cache(struct scsi_disk *sdkp)
> +static int sd_sync_cache(struct scsi_disk *sdkp, struct scsi_sense_hdr *sshdr)
> {
> int retries, res;
> struct scsi_device *sdp = sdkp->device;
> const int timeout = sdp->request_queue->rq_timeout
> * SD_FLUSH_TIMEOUT_MULTIPLIER;
> - struct scsi_sense_hdr sshdr;
> + struct scsi_sense_hdr my_sshdr;
>
> if (!scsi_device_online(sdp))
> return -ENODEV;
>
> + /* caller might not be interested in sense, but we need it */
> + if (!sshdr)
> + sshdr = &my_sshdr;
> +
> for (retries = 3; retries > 0; --retries) {
> unsigned char cmd[10] = { 0 };
>
> @@ -1508,7 +1512,7 @@ static int sd_sync_cache(struct scsi_disk *sdkp)
> * Leave the rest of the command zero to indicate
> * flush everything.
> */
> - res = scsi_execute(sdp, cmd, DMA_NONE, NULL, 0, NULL, &sshdr,
> + res = scsi_execute(sdp, cmd, DMA_NONE, NULL, 0, NULL, sshdr,
> timeout, SD_MAX_RETRIES, 0, RQF_PM, NULL);
> if (res == 0)
> break;
> @@ -1518,11 +1522,12 @@ static int sd_sync_cache(struct scsi_disk *sdkp)
> sd_print_result(sdkp, "Synchronize Cache(10) failed", res);
>
> if (driver_byte(res) & DRIVER_SENSE)
> - sd_print_sense_hdr(sdkp, &sshdr);
> + sd_print_sense_hdr(sdkp, sshdr);
> +
> /* we need to evaluate the error return */
> - if (scsi_sense_valid(&sshdr) &&
> - (sshdr.asc == 0x3a || /* medium not present */
> - sshdr.asc == 0x20)) /* invalid command */
> + if (scsi_sense_valid(sshdr) &&
> + (sshdr->asc == 0x3a || /* medium not present */
> + sshdr->asc == 0x20)) /* invalid command */
> /* this is no error here */
> return 0;
>
> @@ -3323,7 +3328,7 @@ static void sd_shutdown(struct device *dev)
>
> if (sdkp->WCE && sdkp->media_present) {
> sd_printk(KERN_NOTICE, sdkp, "Synchronizing SCSI cache\n");
> - sd_sync_cache(sdkp);
> + sd_sync_cache(sdkp, NULL);
> }
>
> if (system_state != SYSTEM_RESTART && sdkp->device->manage_start_stop) {
> @@ -3335,6 +3340,7 @@ static void sd_shutdown(struct device *dev)
> static int sd_suspend_common(struct device *dev, bool ignore_stop_errors)
> {
> struct scsi_disk *sdkp = dev_get_drvdata(dev);
> + struct scsi_sense_hdr sshdr = { .sense_key = NO_SENSE };
> int ret = 0;
>
> if (!sdkp) /* E.g.: runtime suspend following sd_remove() */
> @@ -3342,8 +3348,17 @@ static int sd_suspend_common(struct device *dev, bool ignore_stop_errors)
>
> if (sdkp->WCE && sdkp->media_present) {
> sd_printk(KERN_NOTICE, sdkp, "Synchronizing SCSI cache\n");
> - ret = sd_sync_cache(sdkp);
> + ret = sd_sync_cache(sdkp, &sshdr);
> if (ret) {
> + /*
> + * If this drive doesn't support sync, there's not much
> + * to do and suspend shouldn't fail.
> + */
> + if (sshdr.sense_key == ILLEGAL_REQUEST) {
> + ret = 0;
> + goto start_stop;
> + }
> +
> /* ignore OFFLINE device */
> if (ret == -ENODEV)
> ret = 0;

I think you need to check for scsi_sense_valid(sshdr) prior to
examining the .sense_key. Also, I believe the check for -ENODEV
should be made prior to checking the sense code, for consistency.
You could also take the opportunity to eliminate both gotos in
this code block, like this (untested):

--
if (ret == -ENODEV)
return 0;

else if ((scsi_sense_valid(sshdr) &&
(sshdr.sense_key == ILLEGAL_REQUEST))
ret = 0;

--

Comments?

-Ewan

> @@ -3351,6 +3366,7 @@ static int sd_suspend_common(struct device *dev, bool ignore_stop_errors)
> }
> }
>
> +start_stop:
> if (sdkp->device->manage_start_stop) {
> sd_printk(KERN_NOTICE, sdkp, "Stopping disk\n");
> /* an error is not worth aborting a system sleep */


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