| Message ID | a6d8c192-2fa5-bc5e-4253-a93a65c0a4fe@redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Tue, Feb 13, 2018 at 10:15:20PM +0800, Jason Wang wrote: > > > On 2018年02月13日 21:21, Christoffer Dall wrote: > >With v4.16-rc1 I see a low of these when running my KVM/ARM test loop: > > > > BUG: using smp_processor_id() in preemptible [00000000] code: vhost-2877/2900 > > caller is debug_smp_processor_id+0x1c/0x28 > > CPU: 0 PID: 2900 Comm: vhost-2877 Not tainted 4.16.0-rc1 #1333 > > Hardware name: APM X-Gene Mustang board (DT) > > Call trace: > > dump_backtrace+0x0/0x180 > > show_stack+0x24/0x30 > > dump_stack+0x8c/0xac > > check_preemption_disabled+0xf8/0x100 > > debug_smp_processor_id+0x1c/0x28 > > xdp_do_flush_map+0x24/0x48 > > tun_sendmsg+0x90/0xa0 > > handle_tx+0x254/0x548 > > handle_tx_kick+0x20/0x30 > > vhost_worker+0xc0/0x158 > > kthread+0x104/0x130 > > ret_from_fork+0x10/0x1c > > > >I confirmed that reverting > > 762c330d670e, "tuntap: add missing xdp flush", 2018-02-07 > >solves the problem for me. > > > >I'm not at all familiar with this part of the kernel and not sure what > >the proper fix is. I'd be grateful if you could take a look and I'm > >happy to help test etc. > > > > Thanks for the reporting. Looking like it was because I try hard to do > batching for XDP devmap which seems a little hard since it assumes XDP was > running inside NAPI. Simply disable preemption can silent the warning but > may lead other issue e.g miss some CPU where the process run previously. The > only way is to disable batching now. > > Please help to test the attached patch. > I can confirm that the patch solves the issue. I put some stress on a VM using tuntap by running netperf in TCP_STREAM, TCP_MAERTS, and TCP_RR on there, and I didn't see any warnings: Tested-by: Christoffer Dall <christoffer.dall@linaro.org> Thanks, -Christoffer
On 2018年02月13日 22:35, Christoffer Dall wrote: > On Tue, Feb 13, 2018 at 10:15:20PM +0800, Jason Wang wrote: >> >> On 2018年02月13日 21:21, Christoffer Dall wrote: >>> With v4.16-rc1 I see a low of these when running my KVM/ARM test loop: >>> >>> BUG: using smp_processor_id() in preemptible [00000000] code: vhost-2877/2900 >>> caller is debug_smp_processor_id+0x1c/0x28 >>> CPU: 0 PID: 2900 Comm: vhost-2877 Not tainted 4.16.0-rc1 #1333 >>> Hardware name: APM X-Gene Mustang board (DT) >>> Call trace: >>> dump_backtrace+0x0/0x180 >>> show_stack+0x24/0x30 >>> dump_stack+0x8c/0xac >>> check_preemption_disabled+0xf8/0x100 >>> debug_smp_processor_id+0x1c/0x28 >>> xdp_do_flush_map+0x24/0x48 >>> tun_sendmsg+0x90/0xa0 >>> handle_tx+0x254/0x548 >>> handle_tx_kick+0x20/0x30 >>> vhost_worker+0xc0/0x158 >>> kthread+0x104/0x130 >>> ret_from_fork+0x10/0x1c >>> >>> I confirmed that reverting >>> 762c330d670e, "tuntap: add missing xdp flush", 2018-02-07 >>> solves the problem for me. >>> >>> I'm not at all familiar with this part of the kernel and not sure what >>> the proper fix is. I'd be grateful if you could take a look and I'm >>> happy to help test etc. >>> >> Thanks for the reporting. Looking like it was because I try hard to do >> batching for XDP devmap which seems a little hard since it assumes XDP was >> running inside NAPI. Simply disable preemption can silent the warning but >> may lead other issue e.g miss some CPU where the process run previously. The >> only way is to disable batching now. >> >> Please help to test the attached patch. >> > I can confirm that the patch solves the issue. I put some stress on a > VM using tuntap by running netperf in TCP_STREAM, TCP_MAERTS, and TCP_RR > on there, and I didn't see any warnings: > > Tested-by: Christoffer Dall <christoffer.dall@linaro.org> > > Thanks, > -Christoffer Thanks for the testing. Will post a formal patch soon.
From 289267a71bc417bd86aa0040d2f3822e9c5aee37 Mon Sep 17 00:00:00 2001
From: Jason Wang <jasowang@redhat.com>
Date: Tue, 13 Feb 2018 22:06:04 +0800
Subject: [PATCH] tuntap: try not batch packets for devmap
Commit 762c330d670e ("tuntap: add missing xdp flush") tries to fix the
devmap stall caused by missed xdp flush by counting the pending xdp
redirected packets and flush when it exceeds NAPI_POLL_WEIGHT or
MSG_MORE is clear. This may lead BUG() since xdp_do_flush() was
called under process context with preemption enabled. Simply disable
preemption may silent the warning but be not enough since process may
move between different CPUS during a batch which cause xdp_do_flush()
misses some CPU where the process run previously. For -net, fix this
by simply calling xdp_do_flush() immediately after xdp_do_redirect(),
a side effect is that this removes any possibility of batching which
could be addressed in the future.
Reported-by: Christoffer Dall <christoffer.dall@linaro.org>
Fixes: 762c330d670e ("tuntap: add missing xdp flush")
Signed-off-by: Jason Wang <jasowang@redhat.com>
---
drivers/net/tun.c | 15 +--------------
1 file changed, 1 insertion(+), 14 deletions(-)
diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index 17e496b..6a4cd97 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 {
@@ -1666,10 +1665,10 @@ 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, xdp_prog);
if (err)
goto err_redirect;
+ xdp_do_flush_map();
rcu_read_unlock();
return NULL;
case XDP_TX:
@@ -1988,11 +1987,6 @@ 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;
}
@@ -2330,12 +2324,6 @@ static int tun_sendmsg(struct socket *sock, struct msghdr *m, size_t total_len)
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;
}
@@ -3167,7 +3155,6 @@ static int tun_chr_open(struct inode *inode, struct file * file)
sock_set_flag(&tfile->sk, SOCK_ZEROCOPY);
memset(&tfile->tx_ring, 0, sizeof(tfile->tx_ring));
- tfile->xdp_pending_pkts = 0;
return 0;
}
--
2.7.4