Re: [PATCH] st: don't doublefree pages from scatterlist

[Mike Christie <michaelc@cs.wisc.edu>]

Hugh Dickins wrote:
> On some architectures, mapping the scatterlist may coalesce entries:
> if that coalesced list is then used for freeing the pages afterwards,
> there's a danger that pages may be doubly freed (and others leaked).
> 
> Fix SCSI Tape's sgl_unmap_user_pages by freeing from the pagelist used
> in sgl_map_user_pages.  Fixes Ryan Richter's crash on x86_64, with Bad
> page state mapcount 2 from sgl_unmap_user_pages, and consequent mayhem.
> 

Is this crash occuring with 2.6.16-rc1? I ask becuase in that kernel the 
scatterlist passed into scsi_execute_async

if (scsi_execute_async(STp->device, cmd, direction,
			&((STp->buffer)->sg[0]), bytes,

is not the same one that gets send down to the device/HBA.

scsi_execute_async takes the scatterlist passed to it from st or sg, 
uses it as a hint to build a request + bios, then later when the request 
is sent to the device a new scatterlist is sent to the device and the 
device does the pci/dma operation on that scatterlist from the 
block/scsi layer.