diff mbox series

[net,2/5] lan966x: execute xdp_do_flush() before napi_complete_done()

Message ID 20230117092533.5804-3-magnus.karlsson@gmail.com (mailing list archive)
State Superseded
Delegated to: Netdev Maintainers
Headers show
Series net: xdp: execute xdp_do_flush() before napi_complete_done() | expand

Checks

Context Check Description
netdev/tree_selection success Clearly marked for net
netdev/fixes_present success Fixes tag present in non-next series
netdev/subject_prefix success Link
netdev/cover_letter success Series has a cover letter
netdev/patch_count success Link
netdev/header_inline success No static functions without inline keyword in header files
netdev/build_32bit success Errors and warnings before: 0 this patch: 0
netdev/cc_maintainers warning 3 maintainers not CCed: edumazet@google.com hawk@kernel.org john.fastabend@gmail.com
netdev/build_clang success Errors and warnings before: 0 this patch: 0
netdev/module_param success Was 0 now: 0
netdev/verify_signedoff success Signed-off-by tag matches author and committer
netdev/check_selftest success No net selftest shell script
netdev/verify_fixes success Fixes tag looks correct
netdev/build_allmodconfig_warn success Errors and warnings before: 0 this patch: 0
netdev/checkpatch success total: 0 errors, 0 warnings, 0 checks, 15 lines checked
netdev/kdoc success Errors and warnings before: 0 this patch: 0
netdev/source_inline success Was 0 now: 0

Commit Message

Magnus Karlsson Jan. 17, 2023, 9:25 a.m. UTC 
From: Magnus Karlsson <magnus.karlsson@intel.com>

Make sure that xdp_do_flush() is always executed before
napi_complete_done(). This is important for two reasons. First, a
redirect to an XSKMAP assumes that a call to xdp_do_redirect() from
napi context X on CPU Y will be follwed by a xdp_do_flush() from the
same napi context and CPU. This is not guaranteed if the
napi_complete_done() is executed before xdp_do_flush(), as it tells
the napi logic that it is fine to schedule napi context X on another
CPU. Details from a production system triggering this bug using the
veth driver can be found following the first link below.

The second reason is that the XDP_REDIRECT logic in itself relies on
being inside a single NAPI instance through to the xdp_do_flush() call
for RCU protection of all in-kernel data structures. Details can be
found in the second link below.

Fixes: a825b611c7c1 ("net: lan966x: Add support for XDP_REDIRECT")
Signed-off-by: Magnus Karlsson <magnus.karlsson@intel.com>
Link: https://lore.kernel.org/r/20221220185903.1105011-1-sbohrer@cloudflare.com
Link: https://lore.kernel.org/all/20210624160609.292325-1-toke@redhat.com/
---
 drivers/net/ethernet/microchip/lan966x/lan966x_fdma.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

Comments

Steen Hegelund Jan. 17, 2023, 11:53 a.m. UTC | #1 
Hi Magnus,

This looks good to me.

Acked-by: Steen Hegelund <Steen.Hegelund@microchip.com>

BR
Steen

On Tue, 2023-01-17 at 10:25 +0100, Magnus Karlsson wrote:
> [Some people who received this message don't often get email from magnus.karlsson@gmail.com. Learn
> why this is important at https://aka.ms/LearnAboutSenderIdentification ]
> 
> EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
> 
> From: Magnus Karlsson <magnus.karlsson@intel.com>
> 
> Make sure that xdp_do_flush() is always executed before
> napi_complete_done(). This is important for two reasons. First, a
> redirect to an XSKMAP assumes that a call to xdp_do_redirect() from
> napi context X on CPU Y will be follwed by a xdp_do_flush() from the
> same napi context and CPU. This is not guaranteed if the
> napi_complete_done() is executed before xdp_do_flush(), as it tells
> the napi logic that it is fine to schedule napi context X on another
> CPU. Details from a production system triggering this bug using the
> veth driver can be found following the first link below.
> 
> The second reason is that the XDP_REDIRECT logic in itself relies on
> being inside a single NAPI instance through to the xdp_do_flush() call
> for RCU protection of all in-kernel data structures. Details can be
> found in the second link below.
> 
> Fixes: a825b611c7c1 ("net: lan966x: Add support for XDP_REDIRECT")
> Signed-off-by: Magnus Karlsson <magnus.karlsson@intel.com>
> Link: https://lore.kernel.org/r/20221220185903.1105011-1-sbohrer@cloudflare.com
> Link: https://lore.kernel.org/all/20210624160609.292325-1-toke@redhat.com/
> ---
>  drivers/net/ethernet/microchip/lan966x/lan966x_fdma.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/net/ethernet/microchip/lan966x/lan966x_fdma.c
> b/drivers/net/ethernet/microchip/lan966x/lan966x_fdma.c
> index 5314c064ceae..55b484b10562 100644
> --- a/drivers/net/ethernet/microchip/lan966x/lan966x_fdma.c
> +++ b/drivers/net/ethernet/microchip/lan966x/lan966x_fdma.c
> @@ -608,12 +608,12 @@ static int lan966x_fdma_napi_poll(struct napi_struct *napi, int weight)
>                 lan966x_fdma_rx_reload(rx);
>         }
> 
> -       if (counter < weight && napi_complete_done(napi, counter))
> -               lan_wr(0xff, lan966x, FDMA_INTR_DB_ENA);
> -
>         if (redirect)
>                 xdp_do_flush();
> 
> +       if (counter < weight && napi_complete_done(napi, counter))
> +               lan_wr(0xff, lan966x, FDMA_INTR_DB_ENA);
> +
>         return counter;
>  }
> 
> --
> 2.34.1
>
diff mbox series

Patch

diff --git a/drivers/net/ethernet/microchip/lan966x/lan966x_fdma.c b/drivers/net/ethernet/microchip/lan966x/lan966x_fdma.c
index 5314c064ceae..55b484b10562 100644
--- a/drivers/net/ethernet/microchip/lan966x/lan966x_fdma.c
+++ b/drivers/net/ethernet/microchip/lan966x/lan966x_fdma.c
@@ -608,12 +608,12 @@  static int lan966x_fdma_napi_poll(struct napi_struct *napi, int weight)
 		lan966x_fdma_rx_reload(rx);
 	}
 
-	if (counter < weight && napi_complete_done(napi, counter))
-		lan_wr(0xff, lan966x, FDMA_INTR_DB_ENA);
-
 	if (redirect)
 		xdp_do_flush();
 
+	if (counter < weight && napi_complete_done(napi, counter))
+		lan_wr(0xff, lan966x, FDMA_INTR_DB_ENA);
+
 	return counter;
 }