On Fri, 2018-11-30 at 15:32 -0500, Willem de Bruijn wrote: > From: Willem de Bruijn <will...@google.com> > > With MSG_ZEROCOPY, each skb holds a reference to a struct ubuf_info. > Release of its last reference triggers a completion notification. > > The TCP stack in tcp_sendmsg_locked holds an extra ref independent of > the skbs, because it can build, send and free skbs within its loop, > possibly reaching refcount zero and freeing the ubuf_info too soon. > > The UDP stack currently also takes this extra ref, but does not need > it as all skbs are sent after return from __ip(6)_append_data. > > Avoid the extra refcount_inc and refcount_dec_and_test, and generally > the sock_zerocopy_put in the common path, by passing the initial > reference to the first skb. > > This approach is taken instead of initializing the refcount to 0, as > that would generate error "refcount_t: increment on 0" on the > next skb_zcopy_set. > > Changes > v3 -> v4 > - Move skb_zcopy_set below the only kfree_skb that might cause > a premature uarg destroy before skb_zerocopy_put_abort > - Move the entire skb_shinfo assignment block, to keep that > cacheline access in one place > > Signed-off-by: Willem de Bruijn <will...@google.com>
I like this solution! Acked-by: Paolo Abeni <pab...@redhat.com>
