[SCSI] st: fix a bug in sgl_map_user_pages failure path

Nick and I had already been looking at drivers/scsi/{sg.c,st.c},
brought there by __put_page in sg.c's peculiar sg_rb_correct4mmap,
which we'd like to remove.  But that's irrelevant to your pain, except...

One extract from the patches I'd like to send Doug and Kai for 2.6.15
or 2.6.16 is this below: since the incomplete get_user_pages path omits
to reset res, but has already released all the pages, it will result in
premature freeing of user pages, and behaviour just like you've seen.

Though I'd have thought incomplete get_user_pages was an exceptional
case, and a bit surprised you'd encounter it.  Perhaps there's some
other premature freeing in the driver, and this instance has nothing
whatever to do with it.

If the problem were easily reproducible, it'd be great if you could
try this patch; but I think you've said it's not :-(

Signed-off-by: Kai Makisara <kai.makisara@kolumbus.fi>
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>

diff --git a/drivers/scsi/st.c b/drivers/scsi/st.c
index 770c4324f3d5750e51eae824fd59a985209b9732..b1056d290ae27b25b807fa125a78340540b58163 100644 (file)
--- a/drivers/scsi/st.c
+++ b/drivers/scsi/st.c
@@ -4509,6 +4509,7 @@ static int sgl_map_user_pages(struct scatterlist *sgl, const unsigned int max_pa
        if (res > 0) {
                for (j=0; j < res; j++)
                        page_cache_release(pages[j]);
+               res = 0;
        }
        kfree(pages);
        return res;