[PATCH] igb: cope with large MAX_SKB_FRAGS.

[Corinna Vinschen <vinschen@redhat.com>]

From: Paolo Abeni <pabeni@redhat.com>

Sabrina reports that the igb driver does not cope well with large
MAX_SKB_FRAG values: setting MAX_SKB_FRAG to 45 causes payload
corruption on TX.

The root cause of the issue is that the driver does not take into
account properly the (possibly large) shared info size when selecting
the ring layout, and will try to fit two packets inside the same 4K
page even when the 1st fraglist will trump over the 2nd head.

Address the issue forcing the driver to fit a single packet per page,
leaving there enough room to store the (currently) largest possible
skb_shared_info.

Fixes: 3948b05950fd ("net: introduce a config option to tweak MAX_SKB_FRAG")
Reported-by: Jan Tluka <jtluka@redhat.com>
Reported-by: Jirka Hladky <jhladky@redhat.com>
Reported-by: Sabrina Dubroca <sd@queasysnail.net>
Tested-by: Sabrina Dubroca <sd@queasysnail.net>
Tested-by: Corinna Vinschen <vinschen@redhat.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
---
 drivers/net/ethernet/intel/igb/igb_main.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/net/ethernet/intel/igb/igb_main.c b/drivers/net/ethernet/intel/igb/igb_main.c
index a3f100769e39..22fb2c322bca 100644
--- a/drivers/net/ethernet/intel/igb/igb_main.c
+++ b/drivers/net/ethernet/intel/igb/igb_main.c
@@ -4833,6 +4833,7 @@ static void igb_set_rx_buffer_len(struct igb_adapter *adapter,
 
 #if (PAGE_SIZE < 8192)
 	if (adapter->max_frame_size > IGB_MAX_FRAME_BUILD_SKB ||
+	    SKB_HEAD_ALIGN(adapter->max_frame_size) > (PAGE_SIZE / 2) ||
 	    rd32(E1000_RCTL) & E1000_RCTL_SBP)
 		set_ring_uses_large_buffer(rx_ring);
 #endif
-- 
2.44.0