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Miller" , Jakub Kicinski , Paolo Abeni , Simon Horman , netdev@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH net] gro_cells: Avoid packet re-ordering for cloned skbs Message-ID: <20250120153156.6bff963c@samweis> In-Reply-To: References: <20250109142724.29228-1-tbogendoerfer@suse.de> <20250113122818.2e6292a9@samweis> X-Mailer: Claws Mail 4.3.0 (GTK 3.24.34; x86_64-suse-linux-gnu) Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable X-Rspamd-Queue-Id: 4CC0821182 X-Spam-Score: -4.01 X-Rspamd-Action: no action X-Spamd-Result: default: False [-4.01 / 50.00]; BAYES_HAM(-3.00)[100.00%]; NEURAL_HAM_LONG(-1.00)[-1.000]; MID_RHS_NOT_FQDN(0.50)[]; R_DKIM_ALLOW(-0.20)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; MX_GOOD(-0.01)[]; RCVD_VIA_SMTP_AUTH(0.00)[]; RBL_SPAMHAUS_BLOCKED_OPENRESOLVER(0.00)[2a07:de40:b281:104:10:150:64:97:from]; RCVD_TLS_ALL(0.00)[]; ASN(0.00)[asn:25478, ipnet:::/0, country:RU]; ARC_NA(0.00)[]; TO_DN_SOME(0.00)[]; MIME_TRACE(0.00)[0:+]; RECEIVED_SPAMHAUS_BLOCKED_OPENRESOLVER(0.00)[2a07:de40:b281:106:10:150:64:167:received]; RCPT_COUNT_SEVEN(0.00)[7]; SPAMHAUS_XBL(0.00)[2a07:de40:b281:104:10:150:64:97:from]; FROM_EQ_ENVFROM(0.00)[]; FROM_HAS_DN(0.00)[]; FUZZY_BLOCKED(0.00)[rspamd.com]; RCVD_COUNT_TWO(0.00)[2]; TO_MATCH_ENVRCPT_ALL(0.00)[]; DBL_BLOCKED_OPENRESOLVER(0.00)[suse.de:email,suse.de:dkim,imap1.dmz-prg2.suse.org:rdns,imap1.dmz-prg2.suse.org:helo]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; DKIM_TRACE(0.00)[suse.de:+] X-Rspamd-Server: rspamd1.dmz-prg2.suse.org X-Spam-Flag: NO X-Spam-Level: On Mon, 13 Jan 2025 13:55:18 +0100 Eric Dumazet wrote: > On Mon, Jan 13, 2025 at 12:28=E2=80=AFPM Thomas Bogendoerfer > wrote: > > > > On Thu, 9 Jan 2025 15:56:24 +0100 > > Eric Dumazet wrote: > > =20 > > > On Thu, Jan 9, 2025 at 3:27=E2=80=AFPM Thomas Bogendoerfer > > > wrote: =20 > > > > > > > > gro_cells_receive() passes a cloned skb directly up the stack and > > > > could cause re-ordering against segments still in GRO. To avoid > > > > this copy the skb and let GRO do it's work. > > > > > > > > Fixes: c9e6bc644e55 ("net: add gro_cells infrastructure") > > > > Signed-off-by: Thomas Bogendoerfer > > > > --- > > > > net/core/gro_cells.c | 11 ++++++++++- > > > > 1 file changed, 10 insertions(+), 1 deletion(-) > > > > > > > > diff --git a/net/core/gro_cells.c b/net/core/gro_cells.c > > > > index ff8e5b64bf6b..2f8d688f9d82 100644 > > > > --- a/net/core/gro_cells.c > > > > +++ b/net/core/gro_cells.c > > > > @@ -20,11 +20,20 @@ int gro_cells_receive(struct gro_cells *gcells,= struct sk_buff *skb) > > > > if (unlikely(!(dev->flags & IFF_UP))) > > > > goto drop; > > > > > > > > - if (!gcells->cells || skb_cloned(skb) || netif_elide_gro(de= v)) { > > > > + if (!gcells->cells || netif_elide_gro(dev)) { > > > > +netif_rx: > > > > res =3D netif_rx(skb); > > > > goto unlock; > > > > } > > > > + if (skb_cloned(skb)) { > > > > + struct sk_buff *n; > > > > > > > > + n =3D skb_copy(skb, GFP_KERNEL); =20 > > > > > > I do not think we want this skb_copy(). This is going to fail too oft= en. =20 > > > > ok > > =20 > > > Can you remind us why we have this skb_cloned() check here ? =20 > > > > some fields of the ip/tcp header are going to be changed in the first g= ro > > segment =20 >=20 > Presumably we should test skb_header_cloned() >=20 > This means something like skb_cow_head(skb, 0) could be much more > reasonable than skb_copy(). I don't think this will work, because at that point it's skb->data points at the IPv6 header in my test case (traffic between two namespaces connected via ip6 tunnel over ipvlan). Correct header offsets are set after later, when gro_cells napi routine runs. Do you see another option ? Thomas. --=20 SUSE Software Solutions Germany GmbH HRB 36809 (AG N=C3=BCrnberg) Gesch=C3=A4ftsf=C3=BChrer: Ivo Totev, Andrew McDonald, Werner Knoblich