Re: [PATCH net v2 1/2] Revert "tuntap: add missing xdp flush"

[Sergei Shtylyov]

On 2/22/2018 9:24 AM, Jason Wang wrote:


This reverts commit 762c330d670e3d4b795cf7a8d761866fdd1eef49. The
reason is we try to batch packets for devmap which causes calling
xdp_do_flush() under the process context. Simply disable premmption


   s/under/in/.
   Disabling preemption.


may not work since process may move among processors which lead
xdp_do_flush() to miss some flushes on some processors.

So simply revert the patch, a follow-up path will add the xdp flush
correctly.

Reported-by: Christoffer Dall 
Fixes: 762c330d670e ("tuntap: add missing xdp flush")
Signed-off-by: Jason Wang 

[...]

MBR, Sergei

[PATCH net v2 1/2] Revert "tuntap: add missing xdp flush"

[Jason Wang]

This reverts commit 762c330d670e3d4b795cf7a8d761866fdd1eef49. The
reason is we try to batch packets for devmap which causes calling
xdp_do_flush() under the process context. Simply disable premmption
may not work since process may move among processors which lead
xdp_do_flush() to miss some flushes on some processors.

So simply revert the patch, a follow-up path will add the xdp flush
correctly.

Reported-by: Christoffer Dall 
Fixes: 762c330d670e ("tuntap: add missing xdp flush")
Signed-off-by: Jason Wang 
---
 drivers/net/tun.c | 15 ---
 1 file changed, 15 deletions(-)

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index b52258c..2823a4a 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -181,7 +181,6 @@ struct tun_file {
struct tun_struct *detached;
struct ptr_ring tx_ring;
struct xdp_rxq_info xdp_rxq;
-   int xdp_pending_pkts;
 };
 
 struct tun_flow_entry {
@@ -1662,7 +1661,6 @@ static struct sk_buff *tun_build_skb(struct tun_struct 
*tun,
case XDP_REDIRECT:
get_page(alloc_frag->page);
alloc_frag->offset += buflen;
-   ++tfile->xdp_pending_pkts;
err = xdp_do_redirect(tun->dev, , xdp_prog);
if (err)
goto err_redirect;
@@ -1984,11 +1982,6 @@ static ssize_t tun_chr_write_iter(struct kiocb *iocb, 
struct iov_iter *from)
result = tun_get_user(tun, tfile, NULL, from,
  file->f_flags & O_NONBLOCK, false);
 
-   if (tfile->xdp_pending_pkts) {
-   tfile->xdp_pending_pkts = 0;
-   xdp_do_flush_map();
-   }
-
tun_put(tun);
return result;
 }
@@ -2325,13 +2318,6 @@ static int tun_sendmsg(struct socket *sock, struct 
msghdr *m, size_t total_len)
ret = tun_get_user(tun, tfile, m->msg_control, >msg_iter,
   m->msg_flags & MSG_DONTWAIT,
   m->msg_flags & MSG_MORE);
-
-   if (tfile->xdp_pending_pkts >= NAPI_POLL_WEIGHT ||
-   !(m->msg_flags & MSG_MORE)) {
-   tfile->xdp_pending_pkts = 0;
-   xdp_do_flush_map();
-   }
-
tun_put(tun);
return ret;
 }
@@ -3163,7 +3149,6 @@ static int tun_chr_open(struct inode *inode, struct file 
* file)
sock_set_flag(>sk, SOCK_ZEROCOPY);
 
memset(>tx_ring, 0, sizeof(tfile->tx_ring));
-   tfile->xdp_pending_pkts = 0;
 
return 0;
 }
-- 
2.7.4