This patch series fixes the same issue which was fixed in Xen with commit
97a6d1bb2b658ac85ed88205ccd1ab809899884d ("xen-netfront: Fix handling packets on
compound pages with skb_linearize").
It is relatively easy to create a packet which is small in size but occupies
more than 30 (MAX_PAGE_BUFFER_COUNT-2) pages. Here is a kernel-mode reproducer
which tries sending a packet with only 34 bytes of payload (but on 34 pages)
and fails:
#include <linux/module.h>
#include <linux/init.h>
#include <linux/net.h>
#include <linux/in.h>
#include <net/sock.h>
static int __init sendfb_init(void)
{
struct socket *sock;
int i, ret;
struct sockaddr_in in4_addr = { 0 };
struct page *pages[17];
unsigned long flags;
ret = sock_create_kern(AF_INET, SOCK_STREAM, IPPROTO_TCP, &sock);
if (ret) {
pr_err("failed to create socket: %d!\n", ret);
return ret;
}
in4_addr.sin_family = AF_INET;
/* www.google.com, 74.125.133.99 */
in4_addr.sin_addr.s_addr = cpu_to_be32(0x4a7d8563);
in4_addr.sin_port = cpu_to_be16(80);
ret = sock->ops->connect(sock, (struct sockaddr *)&in4_addr, sizeof(in4_addr), 0);
if (ret) {
pr_err("failed to connect: %d!\n", ret);
return ret;
}
/* We can send up to 17 frags */
flags = MSG_MORE;
for (i = 0; i < 17; i++) {
if (i == 16)
flags = MSG_EOR;
pages[i] = alloc_pages(GFP_KERNEL | __GFP_COMP, 1);
if (!pages[i]) {
pr_err("out of memory!");
goto free_pages;
}
sock->ops->sendpage(sock, pages[i], PAGE_SIZE -1, 2, flags);
}
free_pages:
for (; i > 0; i--)
__free_pages(pages[i - 1], 1);
printk("sendfb_init: test done\n");
return -1;
}
module_init(sendfb_init);
MODULE_LICENSE("GPL");
A try to load such module results in multiple
'kernel: hv_netvsc vmbus_15 eth0: Packet too big: 100' messages as all retries
fail as well. It should also be possible to trigger the issue from userspace, I
expect e.g. NFS under heavy load to get stuck sometimes.
Vitaly Kuznetsov (2):
hv_netvsc: use single existing drop path in netvsc_start_xmit
hv_netvsc: try linearizing big SKBs before dropping them
drivers/net/hyperv/netvsc_drv.c | 39 ++++++++++++++++++++++++++-------------
1 file changed, 26 insertions(+), 13 deletions(-)
--
1.9.3
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