Re: [PATCH 2.6.23.14] SCSI : scsi_device_lookup/scsi_device_lookup_by_targetreturn NULL for an existent scsi_device
From: James Smart
Date: Wed Jan 23 2008 - 09:09:59 EST
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@xxxxxxxxxxx>
---
--- 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;
}
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