Re: [PATCH v4 1/4] lib/scatterlist: Fix mapping iterator when sg->offset is greater than PAGE_SIZE
On Mon, Jun 24, 2019 at 08:35:33PM +0300, Imre Deak wrote: > Hi, > > On Thu, Jun 20, 2019 at 02:02:21PM +0800, Herbert Xu wrote: > > On Mon, Jun 17, 2019 at 09:15:02PM +, Christophe Leroy wrote: > > > All mapping iterator logic is based on the assumption that sg->offset > > > is always lower than PAGE_SIZE. > > > > > > But there are situations where sg->offset is such that the SG item > > > is on the second page. > > could you explain how sg->offset becomes >= PAGE_SIZE? The network stack can produce SG list elements that are longer than PAGE_SIZE. If you the iterate over it one page at a time then the offset can exceed PAGE_SIZE. Cheers, -- Email: Herbert Xu Home Page: http://gondor.apana.org.au/~herbert/ PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
Re: [PATCH v4 1/4] lib/scatterlist: Fix mapping iterator when sg->offset is greater than PAGE_SIZE
Hi,
On Thu, Jun 20, 2019 at 02:02:21PM +0800, Herbert Xu wrote:
> On Mon, Jun 17, 2019 at 09:15:02PM +, Christophe Leroy wrote:
> > All mapping iterator logic is based on the assumption that sg->offset
> > is always lower than PAGE_SIZE.
> >
> > But there are situations where sg->offset is such that the SG item
> > is on the second page.
could you explain how sg->offset becomes >= PAGE_SIZE?
--Imre
> > In that case sg_copy_to_buffer() fails
> > properly copying the data into the buffer. One of the reason is
> > that the data will be outside the kmapped area used to access that
> > data.
> >
> > This patch fixes the issue by adjusting the mapping iterator
> > offset and pgoffset fields such that offset is always lower than
> > PAGE_SIZE.
> >
> > Signed-off-by: Christophe Leroy
> > Fixes: 4225fc8555a9 ("lib/scatterlist: use page iterator in the mapping
> > iterator")
> > Cc: sta...@vger.kernel.org
> > ---
> > lib/scatterlist.c | 9 +++--
> > 1 file changed, 7 insertions(+), 2 deletions(-)
>
> Good catch.
>
> > @@ -686,7 +686,12 @@ static bool sg_miter_get_next_page(struct
> > sg_mapping_iter *miter)
> > sg = miter->piter.sg;
> > pgoffset = miter->piter.sg_pgoffset;
> >
> > - miter->__offset = pgoffset ? 0 : sg->offset;
> > + offset = pgoffset ? 0 : sg->offset;
> > + while (offset >= PAGE_SIZE) {
> > + miter->piter.sg_pgoffset = ++pgoffset;
> > + offset -= PAGE_SIZE;
> > + }
>
> How about
>
> miter->piter.sg_pgoffset += offset >> PAGE_SHIFT;
> offset &= PAGE_SIZE - 1;
>
> Thanks,
> --
> Email: Herbert Xu
> Home Page: http://gondor.apana.org.au/~herbert/
> PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
Re: [PATCH v4 1/4] lib/scatterlist: Fix mapping iterator when sg->offset is greater than PAGE_SIZE
On Mon, Jun 17, 2019 at 09:15:02PM +, Christophe Leroy wrote:
> All mapping iterator logic is based on the assumption that sg->offset
> is always lower than PAGE_SIZE.
>
> But there are situations where sg->offset is such that the SG item
> is on the second page. In that case sg_copy_to_buffer() fails
> properly copying the data into the buffer. One of the reason is
> that the data will be outside the kmapped area used to access that
> data.
>
> This patch fixes the issue by adjusting the mapping iterator
> offset and pgoffset fields such that offset is always lower than
> PAGE_SIZE.
>
> Signed-off-by: Christophe Leroy
> Fixes: 4225fc8555a9 ("lib/scatterlist: use page iterator in the mapping
> iterator")
> Cc: sta...@vger.kernel.org
> ---
> lib/scatterlist.c | 9 +++--
> 1 file changed, 7 insertions(+), 2 deletions(-)
Good catch.
> @@ -686,7 +686,12 @@ static bool sg_miter_get_next_page(struct
> sg_mapping_iter *miter)
> sg = miter->piter.sg;
> pgoffset = miter->piter.sg_pgoffset;
>
> - miter->__offset = pgoffset ? 0 : sg->offset;
> + offset = pgoffset ? 0 : sg->offset;
> + while (offset >= PAGE_SIZE) {
> + miter->piter.sg_pgoffset = ++pgoffset;
> + offset -= PAGE_SIZE;
> + }
How about
miter->piter.sg_pgoffset += offset >> PAGE_SHIFT;
offset &= PAGE_SIZE - 1;
Thanks,
--
Email: Herbert Xu
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
