Re: [BUG 2.6.17-git] kmem_cache_create: duplicate cache scsi_cmd_cache

Erik Mouw
2006-05-12T20:30:19Z

On Fri, May 12, 2006 at 01:58:45PM -0500, James Bottomley wrote:
> On Fri, 2006-05-12 at 12:47 -0500, James Bottomley wrote:
> > I'll look at the release paths and see if I can work out what it is.
>
> OK, here's the scoop. The problem patch adds a get of driverfs_dev in
> add_disk(), but doesn't put it again until disk_release() (which occurs
> on final put_disk() of the gendisk).
>
> However, in SCSI, the driverfs_dev is the sdev_gendev. That means
> there's a reference held on sdev_gendev until final disk put.
> Unfortunately, we use the driver model driver_remove to trigger
> del_gendisk (which removes the gendisk from visibility and decrements
> the refcount), so we've introduced an unbreakable deadlock in the
> reference counting with this.

That explains why I could only trigger the bug with a disk attached to
the controller.

Thanks for figuring out,

Erik

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