diff mbox series

[net,v2,4/5] dpaa_eth: execute xdp_do_flush() before napi_complete_done()

Message ID 20230125074901.2737-5-magnus.karlsson@gmail.com (mailing list archive)
State Accepted
Commit b534013798b77f81a36f36dafd59bab9de837619
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 fail 1 blamed authors not CCed: camelia.groza@nxp.com; 4 maintainers not CCed: john.fastabend@gmail.com hawk@kernel.org camelia.groza@nxp.com edumazet@google.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, 18 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. 25, 2023, 7:49 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 followed 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: a1e031ffb422 ("dpaa_eth: add XDP_REDIRECT support")
Signed-off-by: Magnus Karlsson <magnus.karlsson@intel.com>
Acked-by: Toke Høiland-Jørgensen <toke@redhat.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/freescale/dpaa/dpaa_eth.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

Comments

Camelia Alexandra Groza Jan. 25, 2023, 2:58 p.m. UTC | #1 
> -----Original Message-----
> From: Magnus Karlsson <magnus.karlsson@gmail.com>
> Sent: Wednesday, January 25, 2023 9:49
> To: magnus.karlsson@intel.com; bjorn@kernel.org; ast@kernel.org;
> daniel@iogearbox.net; netdev@vger.kernel.org;
> jonathan.lemon@gmail.com; maciej.fijalkowski@intel.com;
> kuba@kernel.org; toke@redhat.com; pabeni@redhat.com;
> davem@davemloft.net; aelior@marvell.com; manishc@marvell.com;
> horatiu.vultur@microchip.com; UNGLinuxDriver@microchip.com;
> mst@redhat.com; jasowang@redhat.com; Ioana Ciornei
> <ioana.ciornei@nxp.com>; Madalin Bucur <madalin.bucur@nxp.com>
> Cc: bpf@vger.kernel.org
> Subject: [PATCH net v2 4/5] dpaa_eth: execute xdp_do_flush() before
> napi_complete_done()
> 
> 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 followed 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: a1e031ffb422 ("dpaa_eth: add XDP_REDIRECT support")
> Signed-off-by: Magnus Karlsson <magnus.karlsson@intel.com>
> Acked-by: Toke Høiland-Jørgensen <toke@redhat.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/
> ---

Acked-by: Camelia Groza <camelia.groza@nxp.com>

Thanks!

>  drivers/net/ethernet/freescale/dpaa/dpaa_eth.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/net/ethernet/freescale/dpaa/dpaa_eth.c
> b/drivers/net/ethernet/freescale/dpaa/dpaa_eth.c
> index 3f8032947d86..027fff9f7db0 100644
> --- a/drivers/net/ethernet/freescale/dpaa/dpaa_eth.c
> +++ b/drivers/net/ethernet/freescale/dpaa/dpaa_eth.c
> @@ -2410,6 +2410,9 @@ static int dpaa_eth_poll(struct napi_struct *napi, int
> budget)
> 
>  	cleaned = qman_p_poll_dqrr(np->p, budget);
> 
> +	if (np->xdp_act & XDP_REDIRECT)
> +		xdp_do_flush();
> +
>  	if (cleaned < budget) {
>  		napi_complete_done(napi, cleaned);
>  		qman_p_irqsource_add(np->p, QM_PIRQ_DQRI);
> @@ -2417,9 +2420,6 @@ static int dpaa_eth_poll(struct napi_struct *napi, int
> budget)
>  		qman_p_irqsource_add(np->p, QM_PIRQ_DQRI);
>  	}
> 
> -	if (np->xdp_act & XDP_REDIRECT)
> -		xdp_do_flush();
> -
>  	return cleaned;
>  }
> 
> --
> 2.34.1
diff mbox series

Patch

diff --git a/drivers/net/ethernet/freescale/dpaa/dpaa_eth.c b/drivers/net/ethernet/freescale/dpaa/dpaa_eth.c
index 3f8032947d86..027fff9f7db0 100644
--- a/drivers/net/ethernet/freescale/dpaa/dpaa_eth.c
+++ b/drivers/net/ethernet/freescale/dpaa/dpaa_eth.c
@@ -2410,6 +2410,9 @@  static int dpaa_eth_poll(struct napi_struct *napi, int budget)
 
 	cleaned = qman_p_poll_dqrr(np->p, budget);
 
+	if (np->xdp_act & XDP_REDIRECT)
+		xdp_do_flush();
+
 	if (cleaned < budget) {
 		napi_complete_done(napi, cleaned);
 		qman_p_irqsource_add(np->p, QM_PIRQ_DQRI);
@@ -2417,9 +2420,6 @@  static int dpaa_eth_poll(struct napi_struct *napi, int budget)
 		qman_p_irqsource_add(np->p, QM_PIRQ_DQRI);
 	}
 
-	if (np->xdp_act & XDP_REDIRECT)
-		xdp_do_flush();
-
 	return cleaned;
 }