Re: [RESEND] [PATCH] tcp: fix for splice receive when used with software LRO

[Octavian Purdila <opurdila@ixiacom.com>]

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On Saturday 21 June 2008, Jarek Poplawski wrote:

> Octavian, since these readability changes later in this thread are quite
> substantial, my proposal is to separate them from this bug fix. I'll need
> more time to check them, but they are probably rather for net-next, while
> the bug fix could probably make to current. If you agree with this try to
> resend this once more as a new thread with David in To or Cc (and maybe
> re-diff this to more current tree). You can add my ack below if you like.
>

Yes, I completely agree. Here is yet another patch which incorporates your 
earlier suggestions, hope I get them right. Minimally tested, rediffed to 
current net-2.6. I'll send this one to David once you acked it.

Thanks for the shepherding :) ,
tavi






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commit 41f5beb8a6e12e0c2588aee82ba68c46baf9d5f2
Author: Octavian Purdila <opurdila@ixiacom.com>
Date:   Sat Jun 21 03:17:10 2008 +0300

    tcp: fix for splice receive when used with software LRO
    
    If an skb has nr_frags set to zero but its frag_list is not empty (as
    it can happen if software LRO is enabled), and a previous
    tcp_read_sock has consumed the linear part of the skb, then
    __skb_splice_bits:
    
    (a) incorrectly reports an error and
    
    (b) forgets to update the offset to account for the linear part
    
    Any of the two problems will cause the subsequent __skb_splice_bits
    call (the one that handles the frag_list skbs) to either skip data,
    or, if the unadjusted offset is greater then the size of the next skb
    in the frag_list, make tcp_splice_read loop forever.
    
    Signed-off-by: Octavian Purdila <opurdila@ixiacom.com>

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 1e556d3..d912982 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -1290,7 +1290,6 @@ static int __skb_splice_bits(struct sk_buff *skb, unsigned int *offset,
 			     unsigned int *total_len,
 			     struct splice_pipe_desc *spd)
 {
-	unsigned int nr_pages = spd->nr_pages;
 	unsigned int poff, plen, len, toff, tlen;
 	int headlen, seg;
 
@@ -1340,7 +1339,7 @@ static int __skb_splice_bits(struct sk_buff *skb, unsigned int *offset,
 		 * in going over fragments when the output is full.
 		 */
 		if (spd_fill_page(spd, virt_to_page(p), plen, poff, skb))
-			goto done;
+			goto err;
 
 		tlen -= plen;
 	}
@@ -1370,17 +1369,15 @@ map_frag:
 			break;
 
 		if (spd_fill_page(spd, f->page, plen, poff, skb))
-			break;
+			goto err;
 
 		tlen -= plen;
 	}
 
-done:
-	if (spd->nr_pages - nr_pages) {
-		*offset = 0;
-		*total_len = tlen;
-		return 0;
-	}
+	*offset = toff;
+	*total_len = tlen;
+
+	return 0;
 err:
 	return 1;
 }