Re: [PATCH V3] scsi: core: put LLD module refcnt after SCSI device is released

[Yi Zhang <yi.zhang@redhat.com>]

Tested-by: Yi Zhang <yi.zhang@redhat.com>

This patch fixed one panic issue which I found on s390x with blktests srp tests.
https://lore.kernel.org/linux-block/CAHj4cs8XNtkzbbiLnFmVu82wYeQpLkVp6_wCtrnbhODay+OP9w@mail.gmail.com/#t

On Thu, Sep 30, 2021 at 8:44 PM Ming Lei <ming.lei@redhat.com> wrote:
>
> SCSI host release is triggered when SCSI device is freed, and we have to
> make sure that LLD module won't be unloaded before SCSI host instance is
> released because shost->hostt is required in host release handler.
>
> So make sure to put LLD module refcnt after SCSI device is released.
>
> Fix one kernel panic of 'BUG: unable to handle page fault for address'
> reported by Changhui and Yi.
>
> Reported-by: Changhui Zhong <czhong@redhat.com>
> Reported-by: Yi Zhang <yi.zhang@redhat.com>
> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Signed-off-by: Ming Lei <ming.lei@redhat.com>
> ---
>  drivers/scsi/scsi.c        |  4 +++-
>  drivers/scsi/scsi_sysfs.c  | 12 ++++++++++++
>  include/scsi/scsi_device.h |  1 +
>  3 files changed, 16 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/scsi/scsi.c b/drivers/scsi/scsi.c
> index b241f9e3885c..291ecc33b1fe 100644
> --- a/drivers/scsi/scsi.c
> +++ b/drivers/scsi/scsi.c
> @@ -553,8 +553,10 @@ EXPORT_SYMBOL(scsi_device_get);
>   */
>  void scsi_device_put(struct scsi_device *sdev)
>  {
> -       module_put(sdev->host->hostt->module);
> +       struct module *mod = sdev->host->hostt->module;
> +
>         put_device(&sdev->sdev_gendev);
> +       module_put(mod);
>  }
>  EXPORT_SYMBOL(scsi_device_put);
>
> diff --git a/drivers/scsi/scsi_sysfs.c b/drivers/scsi/scsi_sysfs.c
> index 86793259e541..9ada26814011 100644
> --- a/drivers/scsi/scsi_sysfs.c
> +++ b/drivers/scsi/scsi_sysfs.c
> @@ -449,9 +449,16 @@ static void scsi_device_dev_release_usercontext(struct work_struct *work)
>         struct scsi_vpd *vpd_pg80 = NULL, *vpd_pg83 = NULL;
>         struct scsi_vpd *vpd_pg0 = NULL, *vpd_pg89 = NULL;
>         unsigned long flags;
> +       struct module *mod;
> +       bool put_mod = false;
>
>         sdev = container_of(work, struct scsi_device, ew.work);
>
> +       if (sdev->put_lld_mod_ref) {
> +               mod = sdev->host->hostt->module;
> +               put_mod = true;
> +       }
> +
>         scsi_dh_release_device(sdev);
>
>         parent = sdev->sdev_gendev.parent;
> @@ -502,11 +509,16 @@ static void scsi_device_dev_release_usercontext(struct work_struct *work)
>
>         if (parent)
>                 put_device(parent);
> +       if (put_mod)
> +               module_put(mod);
>  }
>
>  static void scsi_device_dev_release(struct device *dev)
>  {
>         struct scsi_device *sdp = to_scsi_device(dev);
> +
> +       sdp->put_lld_mod_ref = try_module_get(sdp->host->hostt->module);
> +
>         execute_in_process_context(scsi_device_dev_release_usercontext,
>                                    &sdp->ew);
>  }
> diff --git a/include/scsi/scsi_device.h b/include/scsi/scsi_device.h
> index 430b73bd02ac..54b46d590e2d 100644
> --- a/include/scsi/scsi_device.h
> +++ b/include/scsi/scsi_device.h
> @@ -206,6 +206,7 @@ struct scsi_device {
>         unsigned rpm_autosuspend:1;     /* Enable runtime autosuspend at device
>                                          * creation time */
>         unsigned ignore_media_change:1; /* Ignore MEDIA CHANGE on resume */
> +       unsigned put_lld_mod_ref:1;     /* Put LLD module ref in release */
>
>         bool offline_already;           /* Device offline message logged */
>
> --
> 2.31.1
>


-- 
Best Regards,
  Yi Zhang