Re: [PATCH v5 1/3] scsi: core: Add new helper to iterate all devices of host

[Hannes Reinecke]

On 6/12/24 17:06, Wenchao Hao wrote:
> On 6/12/24 4:33 PM, Hannes Reinecke wrote:
> > On 6/5/24 11:17, Wenchao Hao wrote:
> > > shost_for_each_device() would skip devices which is in SDEV_CANCEL or
> > > SDEV_DEL state, for some scenarios, we donot want to skip these devices,
> > > so add a new macro shost_for_each_device_include_deleted() to handle it.
> > >
> > > Following changes are introduced:
> > >
> > > 1. Rework scsi_device_get(), add new helper __scsi_device_get() which
> > >      determine if skip deleted scsi_device by parameter "skip_deleted".
> > > 2. Add new parameter "skip_deleted" to __scsi_iterate_devices() which
> > >      is used when calling __scsi_device_get()
> > > 3. Update shost_for_each_device() to call __scsi_iterate_devices() with
> > >      "skip_deleted" true
> > > 4. Add new macro shost_for_each_device_include_deleted() which call
> > >      __scsi_iterate_devices() with "skip_deleted" false
> > >
> > > Signed-off-by: Wenchao Hao <haowenchao22@xxxxxxxxx>
> > > ---
> > >    drivers/scsi/scsi.c        | 46 ++++++++++++++++++++++++++------------
> > >    include/scsi/scsi_device.h | 25 ++++++++++++++++++---
> > >    2 files changed, 54 insertions(+), 17 deletions(-)
> > >
> > > diff --git a/drivers/scsi/scsi.c b/drivers/scsi/scsi.c
> > > index 3e0c0381277a..5913de543d93 100644
> > > --- a/drivers/scsi/scsi.c
> > > +++ b/drivers/scsi/scsi.c
> > > @@ -735,20 +735,18 @@ int scsi_cdl_enable(struct scsi_device *sdev, bool enable)
> > >        return 0;
> > >    }
> > >    -/**
> > > - * scsi_device_get  -  get an additional reference to a scsi_device
> > > +/*
> > > + * __scsi_device_get  -  get an additional reference to a scsi_device
> > >     * @sdev:    device to get a reference to
> > > - *
> > > - * Description: Gets a reference to the scsi_device and increments the use count
> > > - * of the underlying LLDD module.  You must hold host_lock of the
> > > - * parent Scsi_Host or already have a reference when calling this.
> > > - *
> > > - * This will fail if a device is deleted or cancelled, or when the LLD module
> > > - * is in the process of being unloaded.
> > > + * @skip_deleted: when true, would return failed if device is deleted
> > >     */
> > > -int scsi_device_get(struct scsi_device *sdev)
> > > +static int __scsi_device_get(struct scsi_device *sdev, bool skip_deleted)
> > >    {
> > > -    if (sdev->sdev_state == SDEV_DEL || sdev->sdev_state == SDEV_CANCEL)
> > > +    /*
> > > +     * if skip_deleted is true and device is in removing, return failed
> > > +     */
> > > +    if (skip_deleted &&
> > > +        (sdev->sdev_state == SDEV_DEL || sdev->sdev_state == SDEV_CANCEL))
> > >            goto fail;
> >
> > Nack.
> > SDEV_DEL means the device is about to be deleted, so we _must not_ access it at all.
>
> Sorry I added SDEV_DEL here at hand without understanding what it means.
> Actually, just include scsi_device which is in SDEV_CANCEL would fix the
> issues I described.
>
> The issues are because device removing concurrent with error handle.
> Normally, error handle would not be triggered when scsi_device is in
> SDEV_DEL. Below is my analysis, if it is wrong, please correct me.
>
> If there are scsi_cmnd remain unfinished when removing scsi_device,
> the removing process would waiting for all commands to be finished.
> If commands error happened and trigger error handle, the removing
> process would be blocked until error handle finished, because
> __scsi_remove_device called  del_gendisk() which would wait all
> requests to be finished. So now scsi_device is in SDEV_CANCEL.
>
> If the scsi_device is already in SDEV_DEL, then no scsi_cmnd has been
> dispatched to this scsi_device, then error handle would never triggered.
>
> I want to change the new function __scsi_device_get() as following,
> please help to review.
>
> /*
>   * __scsi_device_get  -  get an additional reference to a scsi_device
>   * @sdev:	device to get a reference to
>   * @skip_canceled: when true, would return failed if device is deleted
>   */
> static int __scsi_device_get(struct scsi_device *sdev, bool skip_canceled)
> {
> 	/*
> 	 * if skip_canceled is true and device is in removing, return failed
> 	 */
> 	if (sdev->sdev_state == SDEV_DEL ||
> 	    (sdev->sdev_state == SDEV_CANCEL && skip_canceled))
> 		goto fail;
> 	if (!try_module_get(sdev->host->hostt->module))
> 		goto fail;
> 	if (!get_device(&sdev->sdev_gendev))
> 		goto fail_put_module;
> 	return 0;
>
> fail_put_module:
> 	module_put(sdev->host->hostt->module);
> fail:
> 	return -ENXIO;
> }
I don't think that's required.
With your above analysis, wouldn't the problem be solved with:

diff --git a/drivers/scsi/scsi_sysfs.c b/drivers/scsi/scsi_sysfs.c
index 775df00021e4..911fcfa80d69 100644
--- a/drivers/scsi/scsi_sysfs.c
+++ b/drivers/scsi/scsi_sysfs.c
@@ -1470,6 +1470,8 @@ void __scsi_remove_device(struct scsi_device *sdev)
        if (sdev->sdev_state == SDEV_DEL)
                return;

+       scsi_block_when_processing_errors(sdev);
+
        if (sdev->is_visible) {
                /*
                 * If scsi_internal_target_block() is running concurrently,

Hmm?

Cheers,

Hannes
--
Dr. Hannes Reinecke                  Kernel Storage Architect
hare@xxxxxxx                                +49 911 74053 688
SUSE Software Solutions GmbH, Frankenstr. 146, 90461 Nürnberg
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