On Mon, 14 Jan 2008 14:11:36 -0800
Michael Reed <mdr@xxxxxxx> wrote:
> We're seeing an occasional panic in sg_add() when class_device_create()
> fails. It's obvious in the code that it uses the pointer to sg_class_member
> even though it's invalid. We do see the "class_device_create failed" message.
>
> class_set_devdata(cl_dev, sdp);
> error = cdev_add(cdev, MKDEV(SCSI_GENERIC_MAJOR, sdp->index), 1);
> if (error)
> goto cdev_add_err;
>
> if (sg_sysfs_valid) {
> struct class_device * sg_class_member;
>
> sg_class_member = class_device_create(sg_sysfs_class, NULL,
> MKDEV(SCSI_GENERIC_MAJOR, sdp->index),
> cl_dev->dev, "%s",
> disk->disk_name);
> if (IS_ERR(sg_class_member))
> printk(KERN_WARNING "sg_add: "
> "class_device_create failed\n");
> class_set_devdata(sg_class_member, sdp);
> ^^^^^^^^^^^^^^^^
> error = sysfs_create_link(&scsidp->sdev_gendev.kobj,
> &sg_class_member->kobj, "generic");
> if (error)
> printk(KERN_ERR "sg_add: unable to make symlink "
> "'generic' back to sg%d\n", sdp->index);
> } else
> printk(KERN_WARNING "sg_add: sg_sys Invalid\n");
>
> I'm uncertain of the correct fix. Perhaps it involves a call to cdev_unmap()?
The following patches work for me:
http://marc.info/?l=linux-scsi&m=120037070303939&w=2
http://marc.info/?l=linux-scsi&m=120037070303941&w=2
> I don't have a good way to test a fix as this problem is not easily
> reproduced.
I used the attached patch (though the fault injection feature can do
something better, I guess).
diff --git a/drivers/scsi/sg.c b/drivers/scsi/sg.c
index 527e2eb..4cdd213 100644
--- a/drivers/scsi/sg.c
+++ b/drivers/scsi/sg.c
@@ -1424,12 +1424,16 @@ sg_add(struct class_device *cl_dev, struct class_interface *cl_intf)
sdp->cdev = cdev;
if (sg_sysfs_valid) {
+ static int count = 0;
struct class_device * sg_class_member;
- sg_class_member = class_device_create(sg_sysfs_class, NULL,
- MKDEV(SCSI_GENERIC_MAJOR, sdp->index),
- cl_dev->dev, "%s",
- disk->disk_name);
+ if (++count % 2)
+ sg_class_member = class_device_create(sg_sysfs_class, NULL,
+ MKDEV(SCSI_GENERIC_MAJOR, sdp->index),
+ cl_dev->dev, "%s",
+ disk->disk_name);
+ else
+ sg_class_member = ERR_PTR(-ENOMEM);
if (IS_ERR(sg_class_member)) {
printk(KERN_ERR "sg_add: "
"class_device_create failed\n");
-
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