From: Pavel Emelyanov Date: Thu, 14 Mar 2013 03:29:40 +0000 (+0000) Subject: skb: Propagate pfmemalloc on skb from head page only X-Git-Url: http://git.lede-project.org./?a=commitdiff_plain;h=cca7af3889bfa343d33d5e657a38d876abd10e58;p=openwrt%2Fstaging%2Fblogic.git skb: Propagate pfmemalloc on skb from head page only Hi. I'm trying to send big chunks of memory from application address space via TCP socket using vmsplice + splice like this mem = mmap(128Mb); vmsplice(pipe[1], mem); /* splice memory into pipe */ splice(pipe[0], tcp_socket); /* send it into network */ When I'm lucky and a huge page splices into the pipe and then into the socket _and_ client and server ends of the TCP connection are on the same host, communicating via lo, the whole connection gets stuck! The sending queue becomes full and app stops writing/splicing more into it, but the receiving queue remains empty, and that's why. The __skb_fill_page_desc observes a tail page of a huge page and erroneously propagates its page->pfmemalloc value onto socket (the pfmemalloc on tail pages contain garbage). Then this skb->pfmemalloc leaks through lo and due to the tcp_v4_rcv sk_filter if (skb->pfmemalloc && !sock_flag(sk, SOCK_MEMALLOC)) /* true */ return -ENOMEM goto release_and_discard; no packets reach the socket. Even TCP re-transmits are dropped by this, as skb cloning clones the pfmemalloc flag as well. That said, here's the proper page->pfmemalloc propagation onto socket: we must check the huge-page's head page only, other pages' pfmemalloc and mapping values do not contain what is expected in this place. However, I'm not sure whether this fix is _complete_, since pfmemalloc propagation via lo also oesn't look great. Both, bit propagation from page to skb and this check in sk_filter, were introduced by c48a11c7 (netvm: propagate page->pfmemalloc to skb), in v3.5 so Mel and stable@ are in Cc. Signed-off-by: Pavel Emelyanov Acked-by: Eric Dumazet Acked-by: Mel Gorman Signed-off-by: David S. Miller --- diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h index 6f2bb860e051..441f5bfdab8e 100644 --- a/include/linux/skbuff.h +++ b/include/linux/skbuff.h @@ -1288,11 +1288,13 @@ static inline void __skb_fill_page_desc(struct sk_buff *skb, int i, * do not lose pfmemalloc information as the pages would not be * allocated using __GFP_MEMALLOC. */ - if (page->pfmemalloc && !page->mapping) - skb->pfmemalloc = true; frag->page.p = page; frag->page_offset = off; skb_frag_size_set(frag, size); + + page = compound_head(page); + if (page->pfmemalloc && !page->mapping) + skb->pfmemalloc = true; } /**