[ovs-dev] [PATCH] datapath: stt: linearize in SKIP_ZERO_COPY case

Neal Shrader neal at digitalocean.com
Fri Jun 22 22:18:50 UTC 2018

During the investigation of a kernel panic, we encountered a condition
that triggered a kernel panic due to a large skb with an unusual
geometry.  Inside of the STT codepath, an effort is made to linearize
such packets to avoid trouble during both fragment reassembly and
segmentation in the linux networking core.

As currently implemented, kernels with CONFIG_SLUB defined will skip
this process because it does not expect an skb with a frag_list to be
present.  This patch removes the assumption, and allows these skb to
be linearized as intended.  We confirmed this corrects the panic we

Reported-by: Johannes Erdfelt <johannes at erdfelt.com>
Reported-at: https://mail.openvswitch.org/pipermail/ovs-discuss/2018-May/046800.html
Requested-by: Pravin Shelar <pshelar at ovn.org>
Signed-off-by: Neal Shrader <neal at digitalocean.com>
 datapath/linux/compat/stt.c | 7 -------
 1 file changed, 7 deletions(-)

diff --git a/datapath/linux/compat/stt.c b/datapath/linux/compat/stt.c
index ca9f03988..64fc550fe 100644
--- a/datapath/linux/compat/stt.c
+++ b/datapath/linux/compat/stt.c
@@ -559,12 +559,6 @@ static int __try_to_segment(struct sk_buff *skb, bool csum_partial,
 static int try_to_segment(struct sk_buff *skb)
-	/* coalesce_skb() since does not generate frag-list no need to
-	 * linearize it here.
-	 */
-	return 0;
 	struct stthdr *stth = stt_hdr(skb);
 	bool csum_partial = !!(stth->flags & STT_CSUM_PARTIAL);
 	bool ipv4 = !!(stth->flags & STT_PROTO_IPV4);
@@ -572,7 +566,6 @@ static int try_to_segment(struct sk_buff *skb)
 	int l4_offset = stth->l4_offset;
 	return __try_to_segment(skb, csum_partial, ipv4, tcp, l4_offset);
 static int segment_skb(struct sk_buff **headp, bool csum_partial,

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