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SubjectRe: [PATCH 1/6] scsi_dh: get module reference outside of device handler
On 10/19/2014 05:59 PM, Christoph Hellwig wrote:
> We need to grab a reference to the module before calling the attach
> routines to avoid a small race vs module removal. It also cleans up
> the code significantly as a side effect.
>
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
> drivers/scsi/device_handler/scsi_dh.c | 31 ++++++++++++++++++++---------
> drivers/scsi/device_handler/scsi_dh_alua.c | 4 ----
> drivers/scsi/device_handler/scsi_dh_emc.c | 4 ----
> drivers/scsi/device_handler/scsi_dh_hp_sw.c | 4 ----
> drivers/scsi/device_handler/scsi_dh_rdac.c | 4 ----
> 5 files changed, 22 insertions(+), 25 deletions(-)
>
> diff --git a/drivers/scsi/device_handler/scsi_dh.c b/drivers/scsi/device_handler/scsi_dh.c
> index 33e422e..1a8dbf3 100644
> --- a/drivers/scsi/device_handler/scsi_dh.c
> +++ b/drivers/scsi/device_handler/scsi_dh.c
> @@ -102,23 +102,36 @@ static int scsi_dh_handler_attach(struct scsi_device *sdev,
>
> if (sdev->scsi_dh_data) {
> if (sdev->scsi_dh_data->scsi_dh != scsi_dh)
> - err = -EBUSY;
> - else
> - kref_get(&sdev->scsi_dh_data->kref);
> - } else if (scsi_dh->attach) {
> + return -EBUSY;
> +
> + kref_get(&sdev->scsi_dh_data->kref);
> + return 0;
> + }
> +
> + if (scsi_dh->attach) {
> + if (!try_module_get(scsi_dh->module))
> + return -EINVAL;
> +
> err = scsi_dh->attach(sdev);
> - if (!err) {
> - kref_init(&sdev->scsi_dh_data->kref);
> - sdev->scsi_dh_data->sdev = sdev;
> + if (err) {
> + module_put(scsi_dh->module);
> + return err;
> }
> +
> + kref_init(&sdev->scsi_dh_data->kref);
> + sdev->scsi_dh_data->sdev = sdev;
> }
> return err;
> }
>
> static void __detach_handler (struct kref *kref)
> {
> - struct scsi_dh_data *scsi_dh_data = container_of(kref, struct scsi_dh_data, kref);
> - scsi_dh_data->scsi_dh->detach(scsi_dh_data->sdev);
> + struct scsi_dh_data *scsi_dh_data =
> + container_of(kref, struct scsi_dh_data, kref);
> + struct scsi_device_handler *scsi_dh = scsi_dh_data->scsi_dh;
> +
> + scsi_dh->detach(scsi_dh_data->sdev);
> + module_put(scsi_dh->module);
> }
>
> /*
Is it guaranteed that you cannot call ->attach() for devices which
already have a device_handler attached?
You've skipped the case

scsi_dh != sdev->scsi_dh_data->scsi_dh

IE someone called 'attach()' on a device which already has a
different device_handler attached to it.

Cheers,

Hannes
--
Dr. Hannes Reinecke zSeries & Storage
hare@suse.de +49 911 74053 688
SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: J. Hawn, J. Guild, F. Imendörffer, HRB 16746 (AG Nürnberg)
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