io_uring/net: fix overexcessive retries

Length parameter of io_sg_from_iter() can be smaller than the iterator's
size, as it's with TCP, so when we set from->count at the end of the
function we truncate the iterator forcing TCP to return preliminary with
a short send. It affects zerocopy sends with large payload sizes and
leads to retries and possible request failures.

Fixes: 3ff1a0d395c00 ("io_uring: enable managed frags with register buffers")
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/0bc0d5179c665b4ef5c328377c84c7a1f298467e.1661530037.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/io_uring/net.c b/io_uring/net.c
index 0af8a02df580f4933fdd42e8957eb8f63e59f369..7a5468cc905e74d2c2704aca1271ce8a318a1da8 100644 (file)
--- a/io_uring/net.c
+++ b/io_uring/net.c
@@ -956,7 +956,7 @@ static int io_sg_from_iter(struct sock *sk, struct sk_buff *skb,
        shinfo->nr_frags = frag;
        from->bvec += bi.bi_idx;
        from->nr_segs -= bi.bi_idx;
-       from->count = bi.bi_size;
+       from->count -= copied;
        from->iov_offset = bi.bi_bvec_done;
 
        skb->data_len += copied;