lkml.org 
[lkml]   [2008]   [Jan]   [23]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
SubjectRe: [PATCH 2.6.23.14] SCSI : scsi_device_lookup/scsi_device_lookup_by_target return NULL for an existent scsi_device

This sounds like a return to the old behavior, where sdevs in SDEV_DEL
were ignored. However, it too had lots of bad effects. We'd have to go
back to the threads over the last 2 years that justified resurrecting
the sdev. Start looking at threads like :
http://marc.info/?l=linux-scsi&m=115555788730468&w=2
http://marc.info/?l=linux-scsi&m=116837744314913&w=2
http://marc.info/?l=linux-scsi&m=117139230702785&w=2
http://marc.info/?l=linux-scsi&m=117991046126294&w=2
Also, there's multiple parts to this - the sdev struct, and the sysfs objects
and thus namespace associated with the struct, etc.

So, in my mind, if this reverts to ignoring sdevs in SDEV_DEL, and creates
a duplicate sdev in SDEV_RUNNING, then it's the wrong patch. What should
be considered is where did the resurrection of the sdev go wrong. I
remember that Hannes did some updates
http://marc.info/?l=linux-scsi&m=118215727101887&w=2
but I don't believe these ever got merged upstream. Perhaps that's a good
place to start.

-- james s


Nagendra Tomar wrote:
> __scsi_device_lookup and __scsi_device_lookup_by_target do not
> check for the sdev_state and hence return scsi_devices with
> sdev_state set to SDEV_DEL also. It has the following side effects.
>
> We can have two scsi_devices with the same HBTL queued in
> the scsi_host->__devices/scsi_target->devices list, one
> in the SDEV_DEL state and the other in, say SDEV_RUNNING state.
> If the one in the SDEV_DEL state is before the one in SDEV_RUNNING
> state, (which will almost always be the case) the scsi_device_lookup and
> scsi_device_lookup_by_target will never find the totally legitimate
> scsi_device (the one in the SDEV_RUNNING state).
>
> This is because __scsi_device_lookup/__scsi_device_lookup_by_target
> always returns the first one in the list (which in our case is the
> one with the SDEV_DEL state) and the scsi_device_get() which is called by
> scsi_device_lookup/scsi_device_lookup_by_target will return -ENXIO
> for this scsi_device, resulting in scsi_device_lookup and
> scsi_device_lookup_by_target to return NULL.
>
> So we _cannot_ lookup a perfectly valid device present in the
> list of scsi_devices.
>
> The right thing to do is to not have __scsi_device_lookup
> and __scsi_device_lookup_by_target match a device if the scsi_device
> state is SDEV_DEL. This will also make these functions similar in
> behaviour to their scsi_device_lookup/scsi_device_lookup_by_target
> counterparts, as the comments in the code suggest.
>
> One way by which we can have two scsi_devices in the list is
> as follows.
> Suppose a scsi_device has some outstanding command(s) when
> scsi_remove_device is called for it. Due to the extra ref being held
> by the command in flight, the __scsi_remove_device->put_device call
> will not actually free the scsi_device and it will remain in the
> scsi_device list albeit in the SDEV_DEL state. Now if we do a
> scsi_add_device for the same HBTL, a new device with the same HBTL
> (this one in SDEV_RUNNING state) gets added to the scsi_device list.
>
> Infact if we call scsi_add_device one more time, it happily
> goes ahead and tries to add it once more, as
> scsi_probe_and_add_lun->scsi_device_lookup_by_target does not return
> the already existing device. This will though result in the kobject
> EEXIST warning dump.
>
> The patch below solves the problem described here by not
> returning scsi_devices in SDEV_DEL state, thus allowing scsi_device
> in SDEV_RUNNING state (if any) to be correctly returned, instead.
>
>
> Thanx,
> Tomar
>
>
> Signed-off-by: Nagendra Singh Tomar <nagendra_tomar@adaptec.com>
> ---
>
> --- linux-2.6.23.14/drivers/scsi/scsi.c.orig 2008-01-23 18:06:02.000000000 +0530
> +++ linux-2.6.23.14/drivers/scsi/scsi.c 2008-01-23 19:17:35.000000000 +0530
> @@ -951,7 +951,7 @@ struct scsi_device *__scsi_device_lookup
> struct scsi_device *sdev;
>
> list_for_each_entry(sdev, &starget->devices, same_target_siblings) {
> - if (sdev->lun ==lun)
> + if (sdev->lun == lun && sdev->sdev_state != SDEV_DEL)
> return sdev;
> }
>
> @@ -1008,7 +1008,7 @@ struct scsi_device *__scsi_device_lookup
>
> list_for_each_entry(sdev, &shost->__devices, siblings) {
> if (sdev->channel == channel && sdev->id == id &&
> - sdev->lun ==lun)
> + sdev->lun == lun && sdev->sdev_state != SDEV_DEL)
> return sdev;
> }
>
>
>
> ___________________________________________________________
> Support the World Aids Awareness campaign this month with Yahoo! For Good http://uk.promotions.yahoo.com/forgood/
> -
> To unsubscribe from this list: send the line "unsubscribe linux-scsi" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at http://vger.kernel.org/majordomo-info.html
>


\
 
 \ /
  Last update: 2008-01-23 15:13    [W:0.063 / U:0.328 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site