Messages in this thread | | | Subject | Re: [ 04/21] target/pscsi: Fix page increment | From | "Nicholas A. Bellinger" <> | Date | Mon, 18 Mar 2013 14:00:34 -0700 |
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On Mon, 2013-03-18 at 13:35 +0800, Asias He wrote: > On Sat, Mar 16, 2013 at 02:10:22AM +0000, Ben Hutchings wrote: > > On Tue, 2013-03-12 at 15:44 -0700, Greg Kroah-Hartman wrote: > > > 3.0-stable review patch. If anyone has any objections, please let me know. > > > > > > ------------------ > > > > > > From: Asias He <asias@redhat.com> > > > > > > commit 472b72f2db7831d7dbe22ffdff4adee3bd49b05d upstream. > > > > > > The page++ is wrong. It makes bio_add_pc_page() pointing to a wrong page > > > address if the 'while (len > 0 && data_len > 0) { ... }' loop is > > > executed more than one once. > > > > > > Signed-off-by: Asias He <asias@redhat.com> > > > Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org> > > > Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> > > > > > > --- > > > drivers/target/target_core_pscsi.c | 1 - > > > 1 file changed, 1 deletion(-) > > > > > > --- a/drivers/target/target_core_pscsi.c > > > +++ b/drivers/target/target_core_pscsi.c > > > @@ -1210,7 +1210,6 @@ static int __pscsi_map_task_SG( > > > bio = NULL; > > > } > > > > > > - page++; > > > len -= bytes; > > > data_len -= bytes; > > > off = 0; > > > > So in case a fragment crosses a page boundary, we wrap around to the > > beginning of the same page? That doesn't look right. > > If the fragment crosses a page boundary, what is the correct page > for it? > > Nicholas, can we assume sg->length + sg->offset should be less than PAGE_SIZE here? >
sg->length + sg->offset can be less than or equal to PAGE_SIZE here.
For everything other than tcm_loop + tcm_vhost using externally allocated SGLs, we can expect fragments to never cross the page boundary.
For tcm_loop + tcm_vhost, there are a few special cases with control CDB paylaods (usually going through scsi-generic) where we can have a non zero sg->offset, but at least in the cases I've seen this is still not using SGL elements that exceed PAGE_SIZE.
So, I think this logic is OK for SGLs that cross page boundries, given that it's done outside of the inner loop where *page is set during each for_each_sg(). The case where this logic is broken, and that the 'page ++' was addressing is when sg->length > PAGE_SIZE.
--nab
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