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Tsirkin" To: Koichiro Den Cc: virtualization@lists.linux.dev, jasowang@redhat.com, xuanzhuo@linux.alibaba.com, eperezma@redhat.com, andrew+netdev@lunn.ch, davem@davemloft.net, edumazet@google.com, kuba@kernel.org, pabeni@redhat.com, jiri@resnulli.us, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org Subject: Re: [PATCH net-next v3 1/7] virtio_net: correct netdev_tx_reset_queue() invocation point Message-ID: <20241205101611-mutt-send-email-mst@kernel.org> References: <20241204050724.307544-1-koichiro.den@canonical.com> <20241204050724.307544-2-koichiro.den@canonical.com> <20241205052729-mutt-send-email-mst@kernel.org> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Thu, Dec 05, 2024 at 10:16:35PM +0900, Koichiro Den wrote: > On Thu, Dec 05, 2024 at 09:43:38PM +0900, Koichiro Den wrote: > > On Thu, Dec 05, 2024 at 05:33:36AM -0500, Michael S. Tsirkin wrote: > > > On Wed, Dec 04, 2024 at 02:07:18PM +0900, Koichiro Den wrote: > > > > When virtnet_close is followed by virtnet_open, some TX completions can > > > > possibly remain unconsumed, until they are finally processed during the > > > > first NAPI poll after the netdev_tx_reset_queue(), resulting in a crash > > > > [1]. > > > > > > > > > So it's a bugfix. Why net-next not net? > > > > I was mistaken (I just read netdev-FAQ again). I'll resend to net, with > > adjustments reflecting your feedback. > > > > > > > > > Commit b96ed2c97c79 ("virtio_net: move netdev_tx_reset_queue() call > > > > before RX napi enable") was not sufficient to eliminate all BQL crash > > > > cases for virtio-net. > > > > > > > > This issue can be reproduced with the latest net-next master by running: > > > > `while :; do ip l set DEV down; ip l set DEV up; done` under heavy network > > > > TX load from inside the machine. > > > > > > > > netdev_tx_reset_queue() can actually be dropped from virtnet_open path; > > > > the device is not stopped in any case. For BQL core part, it's just like > > > > traffic nearly ceases to exist for some period. For stall detector added > > > > to BQL, even if virtnet_close could somehow lead to some TX completions > > > > delayed for long, followed by virtnet_open, we can just take it as stall > > > > as mentioned in commit 6025b9135f7a ("net: dqs: add NIC stall detector > > > > based on BQL"). Note also that users can still reset stall_max via sysfs. > > > > > > > > So, drop netdev_tx_reset_queue() from virtnet_enable_queue_pair(). This > > > > eliminates the BQL crashes. Note that netdev_tx_reset_queue() is now > > > > explicitly required in freeze/restore path, so this patch adds it to > > > > free_unused_bufs(). > > > > > > I don't much like that free_unused_bufs now has this side effect. > > > I think would be better to just add a loop in virtnet_restore. > > > Or if you want to keep it there, pls rename the function > > > to hint it does more. > > > > It makes sense. I would go for the former. Thanks. > > Hmm, as Jacob pointed out in v1 > (https://lore.kernel.org/all/20241202181445.0da50076@kernel.org/), > it looks better to follow the rule of thumb. OK then. I'm fine with keeping your code as is, just a squash, and add a comment /* * Rule of thumb is netdev_tx_reset_queue() should follow any * skb freeing not followed by netdev_tx_completed_queue() */ > Taking both suggestions > from Jacob and you, adding a loop to remove_vq_common(), just after > free_unused_bufs(), seems more fitting now, like this: > > static void remove_vq_common(struct virtnet_info *vi) > { > + int i; > + > virtio_reset_device(vi->vdev); > > /* Free unused buffers in both send and recv, if any. */ > free_unused_bufs(vi); > > + /* Tx unused buffers flushed, so reset BQL counter */ > + for (i = 0; i < vi->max_queue_pairs; i++) > + netdev_tx_reset_queue(netdev_get_tx_queue(vi->dev, i)); > + > free_receive_bufs(vi); > > What do you think? > > Thanks, > > -Koichiro Den > > > > > > > > > > > > > > > > > [1]: > > > > ------------[ cut here ]------------ > > > > kernel BUG at lib/dynamic_queue_limits.c:99! > > > > Oops: invalid opcode: 0000 [#1] PREEMPT SMP NOPTI > > > > CPU: 7 UID: 0 PID: 1598 Comm: ip Tainted: G N 6.12.0net-next_main+ #2 > > > > Tainted: [N]=TEST > > > > Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), \ > > > > BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014 > > > > RIP: 0010:dql_completed+0x26b/0x290 > > > > Code: b7 c2 49 89 e9 44 89 da 89 c6 4c 89 d7 e8 ed 17 47 00 58 65 ff 0d > > > > 4d 27 90 7e 0f 85 fd fe ff ff e8 ea 53 8d ff e9 f3 fe ff ff <0f> 0b 01 > > > > d2 44 89 d1 29 d1 ba 00 00 00 00 0f 48 ca e9 28 ff ff ff > > > > RSP: 0018:ffffc900002b0d08 EFLAGS: 00010297 > > > > RAX: 0000000000000000 RBX: ffff888102398c80 RCX: 0000000080190009 > > > > RDX: 0000000000000000 RSI: 000000000000006a RDI: 0000000000000000 > > > > RBP: ffff888102398c00 R08: 0000000000000000 R09: 0000000000000000 > > > > R10: 00000000000000ca R11: 0000000000015681 R12: 0000000000000001 > > > > R13: ffffc900002b0d68 R14: ffff88811115e000 R15: ffff8881107aca40 > > > > FS: 00007f41ded69500(0000) GS:ffff888667dc0000(0000) > > > > knlGS:0000000000000000 > > > > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > > > > CR2: 0000556ccc2dc1a0 CR3: 0000000104fd8003 CR4: 0000000000772ef0 > > > > PKRU: 55555554 > > > > Call Trace: > > > > > > > > ? die+0x32/0x80 > > > > ? do_trap+0xd9/0x100 > > > > ? dql_completed+0x26b/0x290 > > > > ? dql_completed+0x26b/0x290 > > > > ? do_error_trap+0x6d/0xb0 > > > > ? dql_completed+0x26b/0x290 > > > > ? exc_invalid_op+0x4c/0x60 > > > > ? dql_completed+0x26b/0x290 > > > > ? asm_exc_invalid_op+0x16/0x20 > > > > ? dql_completed+0x26b/0x290 > > > > __free_old_xmit+0xff/0x170 [virtio_net] > > > > free_old_xmit+0x54/0xc0 [virtio_net] > > > > virtnet_poll+0xf4/0xe30 [virtio_net] > > > > ? __update_load_avg_cfs_rq+0x264/0x2d0 > > > > ? update_curr+0x35/0x260 > > > > ? reweight_entity+0x1be/0x260 > > > > __napi_poll.constprop.0+0x28/0x1c0 > > > > net_rx_action+0x329/0x420 > > > > ? enqueue_hrtimer+0x35/0x90 > > > > ? trace_hardirqs_on+0x1d/0x80 > > > > ? kvm_sched_clock_read+0xd/0x20 > > > > ? sched_clock+0xc/0x30 > > > > ? kvm_sched_clock_read+0xd/0x20 > > > > ? sched_clock+0xc/0x30 > > > > ? sched_clock_cpu+0xd/0x1a0 > > > > handle_softirqs+0x138/0x3e0 > > > > do_softirq.part.0+0x89/0xc0 > > > > > > > > > > > > __local_bh_enable_ip+0xa7/0xb0 > > > > virtnet_open+0xc8/0x310 [virtio_net] > > > > __dev_open+0xfa/0x1b0 > > > > __dev_change_flags+0x1de/0x250 > > > > dev_change_flags+0x22/0x60 > > > > do_setlink.isra.0+0x2df/0x10b0 > > > > ? rtnetlink_rcv_msg+0x34f/0x3f0 > > > > ? netlink_rcv_skb+0x54/0x100 > > > > ? netlink_unicast+0x23e/0x390 > > > > ? netlink_sendmsg+0x21e/0x490 > > > > ? ____sys_sendmsg+0x31b/0x350 > > > > ? avc_has_perm_noaudit+0x67/0xf0 > > > > ? cred_has_capability.isra.0+0x75/0x110 > > > > ? __nla_validate_parse+0x5f/0xee0 > > > > ? __pfx___probestub_irq_enable+0x3/0x10 > > > > ? __create_object+0x5e/0x90 > > > > ? security_capable+0x3b/0x70 > > > > rtnl_newlink+0x784/0xaf0 > > > > ? avc_has_perm_noaudit+0x67/0xf0 > > > > ? cred_has_capability.isra.0+0x75/0x110 > > > > ? stack_depot_save_flags+0x24/0x6d0 > > > > ? __pfx_rtnl_newlink+0x10/0x10 > > > > rtnetlink_rcv_msg+0x34f/0x3f0 > > > > ? do_syscall_64+0x6c/0x180 > > > > ? entry_SYSCALL_64_after_hwframe+0x76/0x7e > > > > ? __pfx_rtnetlink_rcv_msg+0x10/0x10 > > > > netlink_rcv_skb+0x54/0x100 > > > > netlink_unicast+0x23e/0x390 > > > > netlink_sendmsg+0x21e/0x490 > > > > ____sys_sendmsg+0x31b/0x350 > > > > ? copy_msghdr_from_user+0x6d/0xa0 > > > > ___sys_sendmsg+0x86/0xd0 > > > > ? __pte_offset_map+0x17/0x160 > > > > ? preempt_count_add+0x69/0xa0 > > > > ? __call_rcu_common.constprop.0+0x147/0x610 > > > > ? preempt_count_add+0x69/0xa0 > > > > ? preempt_count_add+0x69/0xa0 > > > > ? _raw_spin_trylock+0x13/0x60 > > > > ? trace_hardirqs_on+0x1d/0x80 > > > > __sys_sendmsg+0x66/0xc0 > > > > do_syscall_64+0x6c/0x180 > > > > entry_SYSCALL_64_after_hwframe+0x76/0x7e > > > > RIP: 0033:0x7f41defe5b34 > > > > Code: 15 e1 12 0f 00 f7 d8 64 89 02 b8 ff ff ff ff eb bf 0f 1f 44 00 00 > > > > f3 0f 1e fa 80 3d 35 95 0f 00 00 74 13 b8 2e 00 00 00 0f 05 <48> 3d 00 > > > > f0 ff ff 77 4c c3 0f 1f 00 55 48 89 e5 48 83 ec 20 89 55 > > > > RSP: 002b:00007ffe5336ecc8 EFLAGS: 00000202 ORIG_RAX: 000000000000002e > > > > RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 00007f41defe5b34 > > > > RDX: 0000000000000000 RSI: 00007ffe5336ed30 RDI: 0000000000000003 > > > > RBP: 00007ffe5336eda0 R08: 0000000000000010 R09: 0000000000000001 > > > > R10: 00007ffe5336f6f9 R11: 0000000000000202 R12: 0000000000000003 > > > > R13: 0000000067452259 R14: 0000556ccc28b040 R15: 0000000000000000 > > > > > > > > [...] > > > > ---[ end Kernel panic - not syncing: Fatal exception in interrupt ]--- > > > > > > > > Fixes: c8bd1f7f3e61 ("virtio_net: add support for Byte Queue Limits") > > > > Cc: # v6.11+ > > > > Signed-off-by: Koichiro Den > > > > --- > > > > drivers/net/virtio_net.c | 2 +- > > > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > > > > > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c > > > > index 64c87bb48a41..48ce8b3881b6 100644 > > > > --- a/drivers/net/virtio_net.c > > > > +++ b/drivers/net/virtio_net.c > > > > @@ -3054,7 +3054,6 @@ static int virtnet_enable_queue_pair(struct virtnet_info *vi, int qp_index) > > > > if (err < 0) > > > > goto err_xdp_reg_mem_model; > > > > > > > > - netdev_tx_reset_queue(netdev_get_tx_queue(vi->dev, qp_index)); > > > > virtnet_napi_enable(vi->rq[qp_index].vq, &vi->rq[qp_index].napi); > > > > virtnet_napi_tx_enable(vi, vi->sq[qp_index].vq, &vi->sq[qp_index].napi); > > > > > > > > @@ -6243,6 +6242,7 @@ static void free_unused_bufs(struct virtnet_info *vi) > > > > struct virtqueue *vq = vi->sq[i].vq; > > > > while ((buf = virtqueue_detach_unused_buf(vq)) != NULL) > > > > virtnet_sq_free_unused_buf(vq, buf); > > > > + netdev_tx_reset_queue(netdev_get_tx_queue(vi->dev, i)); > > > > cond_resched(); > > > > } > > > > > > > > -- > > > > 2.43.0 > > >