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Date: Sat, 20 Mar 2021 10:45:28 +0200
From: Martin Zaharinov <micron10@...il.com>
To: Wei Wang <weiwan@...gle.com>
Cc: "David S . Miller" <davem@...emloft.net>,
Jakub Kicinski <kuba@...nel.org>, netdev@...r.kernel.org,
Alexander Duyck <alexanderduyck@...com>,
Eric Dumazet <edumazet@...gle.com>,
Paolo Abeni <pabeni@...hat.com>,
Hannes Frederic Sowa <hannes@...essinduktion.org>
Subject: Re: [PATCH net v4] net: fix race between napi kthread mode and busy
poll
Hi Wei
Check this:
[ 39.706567] ------------[ cut here ]------------
[ 39.706568] RTNL: assertion failed at net/ipv4/udp_tunnel_nic.c (557)
[ 39.706585] WARNING: CPU: 0 PID: 429 at net/ipv4/udp_tunnel_nic.c:557 __udp_tunnel_nic_reset_ntf+0xea/0x100
[ 39.706594] Modules linked in: i40e(+) nf_nat_sip nf_conntrack_sip nf_nat_pptp nf_conntrack_pptp nf_nat_tftp nf_conntrack_tftp nf_nat_ftp nf_conntrack_ftp nf_nat nf_conntrack nf_defrag_ipv6 nf_defrag_ipv4 acpi_ipmi ipmi_si ipmi_devintf ipmi_msghandler rtc_cmos megaraid_sas
[ 39.706614] CPU: 0 PID: 429 Comm: kworker/0:2 Tainted: G O 5.11.7 #1
[ 39.706618] Hardware name: Supermicro X11DPi-N(T)/X11DPi-NT, BIOS 3.4 11/23/2020
[ 39.706619] Workqueue: events work_for_cpu_fn
[ 39.706627] RIP: 0010:__udp_tunnel_nic_reset_ntf+0xea/0x100
[ 39.706631] Code: c0 79 f1 00 00 0f 85 4e ff ff ff ba 2d 02 00 00 48 c7 c6 45 3c 3a 93 48 c7 c7 40 de 39 93 c6 05 a0 79 f1 00 01 e8 f5 ad 0c 00 <0f> 0b e9 28 ff ff ff 66 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00
[ 39.706634] RSP: 0018:ffffa8390d9b3b38 EFLAGS: 00010292
[ 39.706637] RAX: 0000000000000039 RBX: ffff8e02630b2768 RCX: 00000000ffdfffff
[ 39.706639] RDX: 00000000ffdfffff RSI: ffff8e80ad400000 RDI: 0000000000000001
[ 39.706641] RBP: ffff8e025df72000 R08: ffff8e80bb3fffe8 R09: 00000000ffffffea
[ 39.706643] R10: 00000000ffdfffff R11: 80000000ffe00000 R12: ffff8e02630b2008
[ 39.706645] R13: 0000000000000000 R14: ffff8e024a88ba00 R15: 0000000000000000
[ 39.706646] FS: 0000000000000000(0000) GS:ffff8e40bf800000(0000) knlGS:0000000000000000
[ 39.706649] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 39.706651] CR2: 00000000004d8f40 CR3: 0000002ca140a002 CR4: 00000000001706f0
[ 39.706652] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 39.706654] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[ 39.706656] Call Trace:
[ 39.706658] i40e_setup_pf_switch+0x617/0xf80 [i40e]
[ 39.706683] i40e_probe.part.0.cold+0x8dc/0x109e [i40e]
[ 39.706708] ? acpi_ns_check_object_type+0xd4/0x193
[ 39.706713] ? acpi_ns_check_package_list+0xfd/0x205
[ 39.706716] ? __kmalloc+0x37/0x160
[ 39.706720] ? kmem_cache_alloc+0xcb/0x120
[ 39.706723] ? irq_get_irq_data+0x5/0x20
[ 39.706726] ? mp_check_pin_attr+0xe/0xf0
[ 39.706729] ? irq_get_irq_data+0x5/0x20
[ 39.706731] ? mp_map_pin_to_irq+0xb7/0x2c0
[ 39.706735] ? acpi_register_gsi_ioapic+0x86/0x150
[ 39.706739] ? pci_conf1_read+0x9f/0xf0
[ 39.706743] ? pci_bus_read_config_word+0x2e/0x40
[ 39.706746] local_pci_probe+0x1b/0x40
[ 39.706750] work_for_cpu_fn+0xb/0x20
[ 39.706754] process_one_work+0x1ec/0x350
[ 39.706758] worker_thread+0x24b/0x4d0
[ 39.706760] ? process_one_work+0x350/0x350
[ 39.706762] kthread+0xea/0x120
[ 39.706766] ? kthread_park+0x80/0x80
[ 39.706770] ret_from_fork+0x1f/0x30
[ 39.706774] ---[ end trace 7a203f3ec972a377 ]---
Martin
> On 17 Mar 2021, at 0:36, Wei Wang <weiwan@...gle.com> wrote:
>
> Currently, napi_thread_wait() checks for NAPI_STATE_SCHED bit to
> determine if the kthread owns this napi and could call napi->poll() on
> it. However, if socket busy poll is enabled, it is possible that the
> busy poll thread grabs this SCHED bit (after the previous napi->poll()
> invokes napi_complete_done() and clears SCHED bit) and tries to poll
> on the same napi. napi_disable() could grab the SCHED bit as well.
> This patch tries to fix this race by adding a new bit
> NAPI_STATE_SCHED_THREADED in napi->state. This bit gets set in
> ____napi_schedule() if the threaded mode is enabled, and gets cleared
> in napi_complete_done(), and we only poll the napi in kthread if this
> bit is set. This helps distinguish the ownership of the napi between
> kthread and other scenarios and fixes the race issue.
>
> Fixes: 29863d41bb6e ("net: implement threaded-able napi poll loop support")
> Reported-by: Martin Zaharinov <micron10@...il.com>
> Suggested-by: Jakub Kicinski <kuba@...nel.org>
> Signed-off-by: Wei Wang <weiwan@...gle.com>
> Cc: Alexander Duyck <alexanderduyck@...com>
> Cc: Eric Dumazet <edumazet@...gle.com>
> Cc: Paolo Abeni <pabeni@...hat.com>
> Cc: Hannes Frederic Sowa <hannes@...essinduktion.org>
> ---
> Change since v3:
> - Add READ_ONCE() for thread->state and add comments in
> ____napi_schedule().
>
> include/linux/netdevice.h | 2 ++
> net/core/dev.c | 19 ++++++++++++++++++-
> 2 files changed, 20 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
> index 5b67ea89d5f2..87a5d186faff 100644
> --- a/include/linux/netdevice.h
> +++ b/include/linux/netdevice.h
> @@ -360,6 +360,7 @@ enum {
> NAPI_STATE_IN_BUSY_POLL, /* sk_busy_loop() owns this NAPI */
> NAPI_STATE_PREFER_BUSY_POLL, /* prefer busy-polling over softirq processing*/
> NAPI_STATE_THREADED, /* The poll is performed inside its own thread*/
> + NAPI_STATE_SCHED_THREADED, /* Napi is currently scheduled in threaded mode */
> };
>
> enum {
> @@ -372,6 +373,7 @@ enum {
> NAPIF_STATE_IN_BUSY_POLL = BIT(NAPI_STATE_IN_BUSY_POLL),
> NAPIF_STATE_PREFER_BUSY_POLL = BIT(NAPI_STATE_PREFER_BUSY_POLL),
> NAPIF_STATE_THREADED = BIT(NAPI_STATE_THREADED),
> + NAPIF_STATE_SCHED_THREADED = BIT(NAPI_STATE_SCHED_THREADED),
> };
>
> enum gro_result {
> diff --git a/net/core/dev.c b/net/core/dev.c
> index 6c5967e80132..d3195a95f30e 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -4294,6 +4294,13 @@ static inline void ____napi_schedule(struct softnet_data *sd,
> */
> thread = READ_ONCE(napi->thread);
> if (thread) {
> + /* Avoid doing set_bit() if the thread is in
> + * INTERRUPTIBLE state, cause napi_thread_wait()
> + * makes sure to proceed with napi polling
> + * if the thread is explicitly woken from here.
> + */
> + if (READ_ONCE(thread->state) != TASK_INTERRUPTIBLE)
> + set_bit(NAPI_STATE_SCHED_THREADED, &napi->state);
> wake_up_process(thread);
> return;
> }
> @@ -6486,6 +6493,7 @@ bool napi_complete_done(struct napi_struct *n, int work_done)
> WARN_ON_ONCE(!(val & NAPIF_STATE_SCHED));
>
> new = val & ~(NAPIF_STATE_MISSED | NAPIF_STATE_SCHED |
> + NAPIF_STATE_SCHED_THREADED |
> NAPIF_STATE_PREFER_BUSY_POLL);
>
> /* If STATE_MISSED was set, leave STATE_SCHED set,
> @@ -6968,16 +6976,25 @@ static int napi_poll(struct napi_struct *n, struct list_head *repoll)
>
> static int napi_thread_wait(struct napi_struct *napi)
> {
> + bool woken = false;
> +
> set_current_state(TASK_INTERRUPTIBLE);
>
> while (!kthread_should_stop() && !napi_disable_pending(napi)) {
> - if (test_bit(NAPI_STATE_SCHED, &napi->state)) {
> + /* Testing SCHED_THREADED bit here to make sure the current
> + * kthread owns this napi and could poll on this napi.
> + * Testing SCHED bit is not enough because SCHED bit might be
> + * set by some other busy poll thread or by napi_disable().
> + */
> + if (test_bit(NAPI_STATE_SCHED_THREADED, &napi->state) || woken) {
> WARN_ON(!list_empty(&napi->poll_list));
> __set_current_state(TASK_RUNNING);
> return 0;
> }
>
> schedule();
> + /* woken being true indicates this thread owns this napi. */
> + woken = true;
> set_current_state(TASK_INTERRUPTIBLE);
> }
> __set_current_state(TASK_RUNNING);
> --
> 2.31.0.rc2.261.g7f71774620-goog
>
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