Re: [PATCH] scsi: properly count the number of pages in scsi_req_map_sg()

Bryan Holty
2006-03-23T16:51:58Z

On Thursday 23 March 2006 08:52, Christoph Hellwig wrote:
> On Tue, Mar 21, 2006 at 06:19:12PM +0200, Dan Aloni wrote:
> > These scatterlists can be generated using the sg driver. Though I am
> > actually running a customized version of the sg driver, it seems the
> > conversion from a userspace array of sg_iovec_t to scatterlist stays
> > the same and also applies to the original driver (see
> > st_map_user_pages()).
>
> What kernel version did you reproduce this with? Since 2.6.16 sg should
> obey all request size/alingment limitations. If not that's a bug in
> scsi_execute_async and it's helpers and should be fixed there.
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I am able to reproduce this with 2.6.16-rc5 - 2.6.16. There is a problem in
scsi_req_map_sg which is called by scsi_execute_async.

Currently, scsi_req_map_sg assumes every sgl entry is page aligned. It will
cause later slab corruption by under-allocating the number of bio entries if
sgl[0].offset + sgl[last].length > PAGE_SIZE.

Dan pointed this out, and I have submitted a patch that I believe correctly
fixes the issue. Just waiting for some feedback.

--
Bryan Holty