[PATCH v2] SUNRPC: Fix the recent bv_offset fix

[PATCH v2] SUNRPC: Fix the recent bv_offset fix

[Chuck Lever]

From: Chuck Lever <chuck.lever@oracle.com>

Jeff confirmed his original fix addressed his pynfs test failure,
but this same bug also impacted qemu: accessing qcow2 virtual disks
using direct I/O was failing. Jeff's fix missed that you have to
shorten the bio_vec element by the same amount as you increased
the page offset.

Reported-by: Maxim Levitsky <mlevitsk@redhat.com>
Fixes: c96e2a695e00 ("sunrpc: set the bv_offset of first bvec in svc_tcp_sendmsg")
Tested-by: Maxim Levitsky <mlevitsk@redhat.com>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
---
 net/sunrpc/svcsock.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

v2:
- Correct Maxim's email addresses.

diff --git a/net/sunrpc/svcsock.c b/net/sunrpc/svcsock.c
index 2eb8df44f894..589020ed909d 100644
--- a/net/sunrpc/svcsock.c
+++ b/net/sunrpc/svcsock.c
@@ -1244,8 +1244,10 @@ static int svc_tcp_sendmsg(struct socket *sock, struct xdr_buf *xdr,
 	if (ret != head->iov_len)
 		goto out;
 
-	if (xdr_buf_pagecount(xdr))
+	if (xdr_buf_pagecount(xdr)) {
 		xdr->bvec[0].bv_offset = offset_in_page(xdr->page_base);
+		xdr->bvec[0].bv_len -= offset_in_page(xdr->page_base);
+	}
 
 	msg.msg_flags = MSG_SPLICE_PAGES;
 	iov_iter_bvec(&msg.msg_iter, ITER_SOURCE, xdr->bvec,

Re: [PATCH v2] SUNRPC: Fix the recent bv_offset fix

[Jeff Layton]

On Mon, 2023-08-28 at 09:23 -0400, Chuck Lever wrote:
> From: Chuck Lever <chuck.lever@oracle.com>
> 
> Jeff confirmed his original fix addressed his pynfs test failure,
> but this same bug also impacted qemu: accessing qcow2 virtual disks
> using direct I/O was failing. Jeff's fix missed that you have to
> shorten the bio_vec element by the same amount as you increased
> the page offset.
> 
> Reported-by: Maxim Levitsky <mlevitsk@redhat.com>
> Fixes: c96e2a695e00 ("sunrpc: set the bv_offset of first bvec in svc_tcp_sendmsg")
> Tested-by: Maxim Levitsky <mlevitsk@redhat.com>
> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
> ---
>  net/sunrpc/svcsock.c |    4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> v2:
> - Correct Maxim's email addresses.
> 
> diff --git a/net/sunrpc/svcsock.c b/net/sunrpc/svcsock.c
> index 2eb8df44f894..589020ed909d 100644
> --- a/net/sunrpc/svcsock.c
> +++ b/net/sunrpc/svcsock.c
> @@ -1244,8 +1244,10 @@ static int svc_tcp_sendmsg(struct socket *sock, struct xdr_buf *xdr,
>  	if (ret != head->iov_len)
>  		goto out;
>  
> -	if (xdr_buf_pagecount(xdr))
> +	if (xdr_buf_pagecount(xdr)) {
>  		xdr->bvec[0].bv_offset = offset_in_page(xdr->page_base);
> +		xdr->bvec[0].bv_len -= offset_in_page(xdr->page_base);
> +	}
>  
>  	msg.msg_flags = MSG_SPLICE_PAGES;
>  	iov_iter_bvec(&msg.msg_iter, ITER_SOURCE, xdr->bvec,
> 
> 

Reviewed-by: Jeff Layton <jlayton@kernel.org>