From: Evgeniy Polyakov <johnpol@2ka•mipt.ru>
To: Eric Dumazet <dada1@cosmosbay•com>
Cc: David Miller <davem@davemloft•net>, Jens Axboe <axboe@kernel•dk>,
netdev@vger•kernel.org, Rusty Russell <rusty@rustcorp•com.au>
Subject: Re: [take 2] Fix for the fundamental network/block layer race in sendfile().
Date: Tue, 8 Apr 2008 21:26:52 +0400 [thread overview]
Message-ID: <20080408172652.GA4877@2ka.mipt.ru> (raw)
In-Reply-To: <47FB6C03.3070708@cosmosbay.com>
On Tue, Apr 08, 2008 at 02:58:43PM +0200, Eric Dumazet (dada1@cosmosbay•com) wrote:
> >With this patch it is now guaranteed that data was transferred over the
> >wire after splice/sendfile returns.
> >
> 1) So a nonblocking operation (O_NDELAY) can become a blocking one now ?
No, it should not - ->sendpage() will return -EAGAIN and we will break
from the main loop before going into sleep.
> >P.S. Previous patch was not an April 1 joke as long as this one :)
> >
> >
> Hum, I see you forgot me in CC list, dont try to escape :)
My fault, sorry :)
> >+static void skb_splice_destructor(struct skb_shared_info *shi)
> >+{
> >+ if (shi->nr_frags) {
> >+ int i;
> >+ struct pipe_inode_info *pipe;
> >+
> >+ for (i = 0; i < shi->nr_frags; i++) {
> >+ struct page *page = shi->frags[i].page;
> >+
> >+ if (page->lru.prev == (struct list_head *)page) {
> >+ pipe = (struct pipe_inode_info
> >*)page->lru.next;
> >
> Unless I mistaken, you store in page->lru.next some info to find
> your pipe pointer, assuming it is unique for this page.
>
> What happens if two threads are doing a splice()/sendfile() using the
> same underlying (source) file (and same pages in this file)
Page will be referenced twice (for each thread) and each thread will
have own pipe_inode_info structure, so each one will sleep on own wait
queue and will be awakened separately, where its release counter will be
dropped.
> >diff --git a/fs/splice.c b/fs/splice.c
> >index 0670c91..dcda32e 100644
> >--- a/fs/splice.c
> >+++ b/fs/splice.c
> >@@ -29,6 +29,7 @@
> > #include <linux/syscalls.h>
> > #include <linux/uio.h>
> > #include <linux/security.h>
> >+#include <net/sock.h>
> >
> > /*
> > * Attempt to steal a page from a pipe buffer. This should perhaps go into
> >@@ -535,6 +536,8 @@ static int pipe_to_sendpage(struct pipe_inode_info
> >*pipe,
> > if (!ret) {
> > more = (sd->flags & SPLICE_F_MORE) || sd->len <
> > sd->total_len;
> >
> >+ buf->page->lru.next = (void *)pipe;
> >
> is it really allowed here, are you the only user ot this page ?
Yes, it should be safe - afaics no slab pages or slab allocated data are
allowed in ->sendpage() (there is even BUG_ON() somewhere in
tcp_sendpage()/release code), so both lru pointers can be reused.
--
Evgeniy Polyakov
next prev parent reply other threads:[~2008-04-08 17:27 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2008-03-28 9:20 Network/block layer race Evgeniy Polyakov
2008-03-28 20:40 ` David Miller
2008-03-28 20:56 ` Evgeniy Polyakov
2008-03-28 21:07 ` David Miller
2008-03-28 21:51 ` Evgeniy Polyakov
2008-04-01 16:49 ` Fix for the fundamental network/block layer race in sendfile() Evgeniy Polyakov
2008-04-01 17:14 ` Mika Penttilä
2008-04-01 17:36 ` Evgeniy Polyakov
2008-04-01 17:19 ` Eric Dumazet
2008-04-01 17:47 ` Evgeniy Polyakov
2008-04-01 18:07 ` Evgeniy Polyakov
2008-04-01 19:21 ` Eric Dumazet
2008-04-01 19:45 ` Evgeniy Polyakov
2008-04-01 20:59 ` Eric Dumazet
2008-04-01 21:14 ` Evgeniy Polyakov
2008-04-08 12:25 ` [take 2] " Evgeniy Polyakov
2008-04-08 12:58 ` Eric Dumazet
2008-04-08 17:26 ` Evgeniy Polyakov [this message]
2008-04-08 21:30 ` Evgeniy Polyakov
2008-04-09 11:33 ` Jens Axboe
2011-06-06 16:29 ` IPv6 DNSSL (rfc6106): please include the patch to pass it to user space Carlos Carvalho
2011-06-06 19:40 ` David Miller
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20080408172652.GA4877@2ka.mipt.ru \
--to=johnpol@2ka$(echo .)mipt.ru \
--cc=axboe@kernel$(echo .)dk \
--cc=dada1@cosmosbay$(echo .)com \
--cc=davem@davemloft$(echo .)net \
--cc=netdev@vger$(echo .)kernel.org \
--cc=rusty@rustcorp$(echo .)com.au \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox