* [PATCH 2.6.27.7-9-pae #7 SMP 1/1] networking tcp: Writing tcp socket be atomic
@ 2010-02-03 9:12 john ye
2010-02-03 16:52 ` David Miller
0 siblings, 1 reply; 4+ messages in thread
From: john ye @ 2010-02-03 9:12 UTC (permalink / raw)
To: davem, kuznet, netdev, jmorris, kaber; +Cc: linux-kernel
Subject: [PATCH 2.6.27.7-9-pae #7 SMP 1/1] networking tcp: Writing tcp socket be atomic
from: John Ye <johny@asimco.com.cn>
Writing tcp socket is not atomic in current kernel. When a socket is written by
multi-processes or threads,the other end will read interleaved garbage data.
This simple patch is to resolve this issue, to make the stream socket writing
be atomic under certain data size limit.
Similar to file system pipe ( with a max atomic write limit ), an atomic
socket can be written by multi processes or threads.
But it’s more than pipe. The pipe can only be used by multi processes in a
local system, the atomic stream socket can be used remotely to send data
among machines without user level locking involved.
How to test this patch:
1) apply the patch to kernel and modules, reboot from the new patched kernel
2) #define TCP_ATOMIC 20 in your test.c (TCP_ATOMIC is defined as 20 in kernel)
3) create a tcp socket, set the atomic option.
for example:
int val = 512;
int len = 4;
if(setsockopt(s, IPPROTO_TCP, TCP_ATOMIC, &val, len) == -1) {
perror("setsockopt");
return -1 ;
}
will set the atomic max data size to 512 bytes
to get the current atomic size for socket s,
val = 0;
len = 4;
if(getsockopt(s, IPPROTO_TCP, TCP_ATOMIC, &val, &len) == -1) {
perror("setsockopt");
return -1 ;
}
4) Then, connect to a tcp server, fork a child process.
let both main process and child process write() or send() its own data block to the server.
From the server, the received data bytes will be interleaved if no TCP_ATOMIC is set.
(I have a testing c code ready)
Signed-off-by: John Ye (Seeker) johny@asimco.com.cn
---
--- linux/net/ipv4/tcp.c 2008-12-05 09:48:57.000000000 +0800
+++ linux/net/ipv4/tcp.c 2010-02-03 15:15:11.000000000 +0800
@@ -822,6 +822,7 @@
int mss_now, size_goal;
int err, copied;
long timeo;
+ int atomic; /* is atomic write? johnye. Feb 2, 2010 */
lock_sock(sk);
TCP_CHECK_TIMER(sk);
@@ -849,6 +850,11 @@
if (sk->sk_err || (sk->sk_shutdown & SEND_SHUTDOWN))
goto do_error;
+
+ /* for multi-seg data or too big chunk, no atomic. johnye. */
+ atomic = tp->atomic_size;
+ if(iovlen > 1 || iov->iov_len > atomic) atomic = 0;
+
while (--iovlen >= 0) {
int seglen = iov->iov_len;
unsigned char __user *from = iov->iov_base;
@@ -889,14 +895,28 @@
if (copy > seglen)
copy = seglen;
+ /* if atomic write. johnye */
+ if (atomic)
+ copy = seglen;
+
/* Where to copy to? */
if (skb_tailroom(skb) > 0) {
/* We have some space in skb head. Superb! */
- if (copy > skb_tailroom(skb))
+ /* consider atomic write, johnye */
+ if (copy > skb_tailroom(skb)) {
+ if(atomic)
+ goto skb_page_start; /* q mark yet, johnye */
+
copy = skb_tailroom(skb);
+ }
if ((err = skb_add_data(skb, from, copy)) != 0)
goto do_fault;
- } else {
+
+ goto skb_page_done;
+ //} else {
+ }
+ skb_page_start:
+ {
int merge = 0;
int i = skb_shinfo(skb)->nr_frags;
struct page *page = TCP_PAGE(sk);
@@ -925,8 +945,17 @@
} else
off = 0;
- if (copy > PAGE_SIZE - off)
- copy = PAGE_SIZE - off;
+ /* consider atomic write, johnye */
+ if (copy > PAGE_SIZE - off) {
+ if (atomic && page) {
+ put_page(page);
+ TCP_PAGE(sk) = page = NULL;
+ off = 0;
+ merge = 0;
+ } else {
+ copy = PAGE_SIZE - off;
+ }
+ }
if (!sk_wmem_schedule(sk, copy))
goto wait_for_memory;
@@ -968,6 +997,7 @@
TCP_OFF(sk) = off + copy;
}
+ skb_page_done:
if (!copied)
TCP_SKB_CB(skb)->flags &= ~TCPCB_FLAG_PSH;
@@ -2019,6 +2049,16 @@
lock_sock(sk);
switch (optname) {
+
+ /* set the atomic write max size. johnye */
+ case TCP_ATOMIC:
+ if(val > 1024) {
+ err = -EINVAL;
+ break;
+ }
+ tp->atomic_size = val;
+ break;
+
case TCP_MAXSEG:
/* Values greater than interface MTU won't take effect. However
* at the point when this call is done we typically don't yet
@@ -2276,6 +2316,12 @@
return -EINVAL;
switch (optname) {
+
+ /* get the atomic write max size. johnye */
+ case TCP_ATOMIC:
+ val = tp->atomic_size;
+ break;
+
case TCP_MAXSEG:
val = tp->mss_cache;
if (!val && ((1 << sk->sk_state) & (TCPF_CLOSE | TCPF_LISTEN)))
--- linux/include/linux/tcp.h 2008-10-10 06:13:53.000000000 +0800
+++ linux/include/linux/tcp.h 2010-02-03 13:54:55.000000000 +0800
@@ -97,6 +97,8 @@
#define TCP_CONGESTION 13 /* Congestion control algorithm */
#define TCP_MD5SIG 14 /* TCP MD5 Signature (RFC2385) */
+#define TCP_ATOMIC 20 /* atomic TCP socket writting */
+
#define TCPI_OPT_TIMESTAMPS 1
#define TCPI_OPT_SACK 2
#define TCPI_OPT_WSCALE 4
@@ -411,6 +413,7 @@
#endif
int linger2;
+ u32 atomic_size; /* for atomic tcp socket write, johnye. Feb 2, 2010 */
};
static inline struct tcp_sock *tcp_sk(const struct sock *sk)
---
^ permalink raw reply [flat|nested] 4+ messages in thread* Re: [PATCH 2.6.27.7-9-pae #7 SMP 1/1] networking tcp: Writing tcp socket be atomic
2010-02-03 9:12 [PATCH 2.6.27.7-9-pae #7 SMP 1/1] networking tcp: Writing tcp socket be atomic john ye
@ 2010-02-03 16:52 ` David Miller
2010-02-04 2:03 ` John Ye
0 siblings, 1 reply; 4+ messages in thread
From: David Miller @ 2010-02-03 16:52 UTC (permalink / raw)
To: johny; +Cc: kuznet, netdev, jmorris, kaber, linux-kernel
Locking belongs inside of the application, not in the kernel.
As evidenced by the fact that you had to add new socket options, the
application needs to be modified anyways.
It's therefore just as easy to add the appropriate locking to the
sequences where the application writes over the TCP socket. And
it avoids having to modify the kernel at all.
^ permalink raw reply [flat|nested] 4+ messages in thread
* RE: [PATCH 2.6.27.7-9-pae #7 SMP 1/1] networking tcp: Writing tcp socket be atomic
2010-02-03 16:52 ` David Miller
@ 2010-02-04 2:03 ` John Ye
2010-02-04 2:19 ` David Miller
0 siblings, 1 reply; 4+ messages in thread
From: John Ye @ 2010-02-04 2:03 UTC (permalink / raw)
To: David Miller; +Cc: kuznet, netdev, jmorris, kaber, linux-kernel
David,
Thanks.
The option TCP_ATOMIC is not a must.
We can make atomic be default if the data size is less than a fixed size, just the same as pipe.
For example, if the data size is less than 512, we don't split the data so it goes atomically.
John Ye
-----Original Message-----
From: David Miller [mailto:davem@davemloft.net]
Sent: 2010年2月4日 0:53
To: John Ye
Cc: kuznet@ms2.inr.ac.ru; netdev@vger.kernel.org; jmorris@namei.org; kaber@coreworks.de; linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2.6.27.7-9-pae #7 SMP 1/1] networking tcp: Writing tcp socket be atomic
Locking belongs inside of the application, not in the kernel.
As evidenced by the fact that you had to add new socket options, the
application needs to be modified anyways.
It's therefore just as easy to add the appropriate locking to the
sequences where the application writes over the TCP socket. And
it avoids having to modify the kernel at all.
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH 2.6.27.7-9-pae #7 SMP 1/1] networking tcp: Writing tcp socket be atomic
2010-02-04 2:03 ` John Ye
@ 2010-02-04 2:19 ` David Miller
0 siblings, 0 replies; 4+ messages in thread
From: David Miller @ 2010-02-04 2:19 UTC (permalink / raw)
To: johny; +Cc: kuznet, netdev, jmorris, kaber, linux-kernel
From: "John Ye" <johny@asimco.com.cn>
Date: Thu, 4 Feb 2010 10:03:44 +0800
> The option TCP_ATOMIC is not a must. We can make atomic be default
> if the data size is less than a fixed size, just the same as pipe.
> For example, if the data size is less than 512, we don't split the
> data so it goes atomically.
This completely ignores the core issue.
And that is, for the second time, that the application is where such
atomicity guarentees should be implemented.
And because of that any implementation of your kernel changes are
inappropriate, TCP_ATOMIC socket option or not.
^ permalink raw reply [flat|nested] 4+ messages in thread
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2010-02-03 9:12 [PATCH 2.6.27.7-9-pae #7 SMP 1/1] networking tcp: Writing tcp socket be atomic john ye
2010-02-03 16:52 ` David Miller
2010-02-04 2:03 ` John Ye
2010-02-04 2:19 ` David Miller
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