Hi, On Thu, Jun 20, 2019 at 02:02:21PM +0800, Herbert Xu wrote: > On Mon, Jun 17, 2019 at 09:15:02PM +0000, 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 <christophe.leroy@xxxxxx> > > Fixes: 4225fc8555a9 ("lib/scatterlist: use page iterator in the mapping iterator") > > Cc: stable@xxxxxxxxxxxxxxx > > --- > > 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 <herbert@xxxxxxxxxxxxxxxxxxx> > Home Page: http://gondor.apana.org.au/~herbert/ > PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt