Re: [PATCH] smb: client: Fix error cleanup in smb_extract_iter_to_rdma()

[Stefan Metzmacher]

Hi David,

> > Fix smb_extract_iter_to_rdma() to use pre-decrement, not post-decrement, so
> > that it cleans up the correct slots.
> >
> > Fixes: e5fbdde43017 ("cifs: Add a function to build an RDMA SGE list from an iterator")
> > Closes: https://sashiko.dev/#/patchset/20260326104544.509518-1-dhowells%40redhat.com
> > Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
> > cc: Steve French <sfrench@xxxxxxxxx>
> > cc: Stefan Metzmacher <metze@xxxxxxxxx>
> > cc: Paulo Alcantara <pc@xxxxxxxxxxxxx>
> > cc: Tom Talpey <tom@xxxxxxxxxx>
> > cc: linux-cifs@xxxxxxxxxxxxxxx
> > cc: linux-fsdevel@xxxxxxxxxxxxxxx
> > ---
> >   fs/smb/client/smbdirect.c |    2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/fs/smb/client/smbdirect.c b/fs/smb/client/smbdirect.c
> > index 7d5f66bdbb30..4978755c035c 100644
> > --- a/fs/smb/client/smbdirect.c
> > +++ b/fs/smb/client/smbdirect.c
> > @@ -3394,7 +3394,7 @@ static ssize_t smb_extract_iter_to_rdma(struct iov_iter *iter, size_t len,
> >   
> >   	if (ret < 0) {
> >   		while (rdma->nr_sge > before) {
> > -			struct ib_sge *sge = &rdma->sge[rdma->nr_sge--];
> > +			struct ib_sge *sge = &rdma->sge[--rdma->nr_sge];

Can you please use logic like this?

-               while (state->num_sge > before) {
-                       struct ib_sge *sge = &state->sge[state->num_sge--];
+               for (size_t i = before; i < state->num_sge; i++) {
+                       struct ib_sge *sge = &state->sge[i];

At least for me that is much easier to understand.

And as Greg pointed out we first need a fix for upstream, there
the function is smbdirect_map_sges_from_iter in fs/smb/smbdirect/connection.c

Also the commit message needs to be adjusted for the new name.

Then we need a backportable fix for smb_extract_iter_to_rdma in
fs/smb/client/smbdirect.c with the same logic.

Thanks!
metze

> >   			ib_dma_unmap_single(rdma->device, sge->addr, sge->length,
> >   					    rdma->direction);
> <formletter>
>
> This is not the correct way to submit patches for inclusion in the
> stable kernel tree.  Please read:
>      https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html
> for how to do this properly.
>
> </formletter>