* Lockdep warning after c0feea594e058223973db94c1c32a830c9807c86
@ 2022-10-12 21:08 sdf
2022-10-13 16:45 ` Martin KaFai Lau
2022-10-13 20:39 ` Jakub Sitnicki
0 siblings, 2 replies; 5+ messages in thread
From: sdf @ 2022-10-12 21:08 UTC (permalink / raw)
To: john.fastabend, jakub; +Cc: netdev, bpf
Hi John & Jakub,
Upstream commit c0feea594e05 ("workqueue: don't skip lockdep work
dependency in cancel_work_sync()") seems to trigger the following
lockdep warning during test_prog's sockmap_listen:
[ +0.003631] WARNING: possible circular locking dependency detected
[ +0.003647] 6.0.0-dbx-DEV #10 Not tainted
[ +0.002402] ------------------------------------------------------
[ +0.003685] kworker/1:0/23 is trying to acquire lock:
[ +0.003012] ffff888100b1e3f0 (sk_lock-AF_INET){+.+.}-{0:0}, at:
tcp_sendpage+0x28/0x80
[ +0.004655]
but task is already holding lock:
[ +0.003434] ffff88810642c360 (&psock->work_mutex){+.+.}-{3:3}, at:
sk_psock_backlog+0x2e/0x370
[ +0.005043]
which lock already depends on the new lock.
[ +0.004792]
the existing dependency chain (in reverse order) is:
[ +0.004397]
-> #2 (&psock->work_mutex){+.+.}-{3:3}:
[ +0.003732] __mutex_lock_common+0xdf/0xe70
[ +0.002958] mutex_lock_nested+0x20/0x30
[ +0.002685] sk_psock_backlog+0x2e/0x370
[ +0.002689] process_one_work+0x22c/0x3b0
[ +0.002815] worker_thread+0x21b/0x400
[ +0.002652] kthread+0xf7/0x110
[ +0.002406] ret_from_fork+0x1f/0x30
[ +0.002512]
-> #1 ((work_completion)(&psock->work)){+.+.}-{0:0}:
[ +0.004457] __flush_work+0x6b/0xd0
[ +0.002638] __cancel_work_timer+0x11a/0x1a0
[ +0.002973] cancel_work_sync+0x10/0x20
[ +0.002724] sk_psock_stop+0x298/0x2b0
[ +0.002969] sock_map_close+0xd8/0x140
[ +0.002739] inet_release+0x57/0x80
[ +0.002475] sock_close+0x4b/0xe0
[ +0.002380] __fput+0x101/0x230
[ +0.002347] ____fput+0xe/0x10
[ +0.002259] task_work_run+0x5d/0xb0
[ +0.002535] exit_to_user_mode_loop+0xd6/0xf0
[ +0.003019] exit_to_user_mode_prepare+0xa6/0x100
[ +0.003201] syscall_exit_to_user_mode+0x5b/0x160
[ +0.003145] do_syscall_64+0x49/0x80
[ +0.002549] entry_SYSCALL_64_after_hwframe+0x63/0xcd
[ +0.003410]
-> #0 (sk_lock-AF_INET){+.+.}-{0:0}:
[ +0.003906] __lock_acquire+0x16f4/0x30c0
[ +0.002837] lock_acquire+0xc5/0x1c0
[ +0.002599] lock_sock_nested+0x32/0x80
[ +0.002690] tcp_sendpage+0x28/0x80
[ +0.002435] inet_sendpage+0x7b/0xe0
[ +0.002534] kernel_sendpage+0x5d/0xa0
[ +0.002709] skb_send_sock+0x24b/0x2d0
[ +0.002662] sk_psock_backlog+0x106/0x370
[ +0.002908] process_one_work+0x22c/0x3b0
[ +0.002736] worker_thread+0x21b/0x400
[ +0.002552] kthread+0xf7/0x110
[ +0.002252] ret_from_fork+0x1f/0x30
[ +0.002480]
other info that might help us debug this:
[ +0.004778] Chain exists of:
sk_lock-AF_INET --> (work_completion)(&psock->work) -->
&psock->work_mutex
[ +0.007265] Possible unsafe locking scenario:
[ +0.003496] CPU0 CPU1
[ +0.002717] ---- ----
[ +0.002809] lock(&psock->work_mutex);
[ +0.002335]
lock((work_completion)(&psock->work));
[ +0.004496] lock(&psock->work_mutex);
[ +0.003766] lock(sk_lock-AF_INET);
[ +0.002185]
*** DEADLOCK ***
[ +0.003600] 3 locks held by kworker/1:0/23:
[ +0.002698] #0: ffff888100055138 ((wq_completion)events){+.+.}-{0:0},
at: process_one_work+0x1d6/0x3b0
[ +0.005552] #1: ffffc900001e7e58
((work_completion)(&psock->work)){+.+.}-{0:0}, at:
process_one_work+0x1fc/0x3b0
[ +0.006085] #2: ffff88810642c360 (&psock->work_mutex){+.+.}-{3:3}, at:
sk_psock_backlog+0x2e/0x370
[ +0.005424]
stack backtrace:
[ +0.002689] CPU: 1 PID: 23 Comm: kworker/1:0 Not tainted 6.0.0-dbx-DEV #10
[ +0.004086] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
rel-1.16.0-0-gd239552ce722-prebuilt.qemu.org 04/01/2014
[ +0.006806] Workqueue: events sk_psock_backlog
[ +0.002699] Call Trace:
[ +0.001577] <TASK>
[ +0.001350] dump_stack_lvl+0x69/0xaa
[ +0.002225] dump_stack+0x10/0x12
[ +0.002051] print_circular_bug+0x289/0x290
[ +0.002531] check_noncircular+0x12c/0x140
[ +0.002578] __lock_acquire+0x16f4/0x30c0
[ +0.002483] ? ret_from_fork+0x1f/0x30
[ +0.002297] ? __this_cpu_preempt_check+0x13/0x20
[ +0.002869] ? lock_is_held_type+0xf8/0x160
[ +0.002511] lock_acquire+0xc5/0x1c0
[ +0.002165] ? tcp_sendpage+0x28/0x80
[ +0.002367] lock_sock_nested+0x32/0x80
[ +0.002401] ? tcp_sendpage+0x28/0x80
[ +0.002262] tcp_sendpage+0x28/0x80
[ +0.002148] inet_sendpage+0x7b/0x[ 12.231432] sysrq: Power Off
e0
[ +0.002202[ 12.234545] kvm: exiting hardware virtualization
] kernel_sendpage+0x5d/0xa0
[ +0.002277] skb_send_sock+0x24b/0x2d0
[ +0.002278] ? _raw_spin_unlock_irqrestore+0x35/0x60
[ +0.003030] ? __this_cpu_preempt_check+0x13/0x20
[ +0.002861] ? lockdep_hardirqs_on+0x97/0x140
[ +0.002685] ? trace_hardirqs_on+0x47/0x50
[ +0.002576] ? _raw_spin_unlock_irqrestore+0x40/0x60
[ +0.003207] sk_psock_backlog+0x106/0x370
[ +0.002476] process_one_work+0x22c/0x3b0
[ +0.002473] worker_thread+0x21b/0x400
[ +0.002335] kthread+0xf7/0x110
[ +0.001954] ? rcu_lock_release+0x20/0x20
[ +0.002444] ? kthread_blkcg+0x30/0x30
[ +0.002325] ret_from_fork+0x1f/0x30
[ +0.002221] </TASK>
This is on bpf-next:
commit d31ada3b511141f4b78cae5a05cc2dad887c40b7 (HEAD -> bpf-next,
bpf-next/master)
Author: David Vernet <void@manifault.com>
Date: Tue Oct 11 11:52:55 2022 -0500
selftests/bpf: Alphabetize DENYLISTs
Are you ware? Any idea what's wrong?
Is there some stable fix I'm missing in bpf-next?
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: Lockdep warning after c0feea594e058223973db94c1c32a830c9807c86
2022-10-12 21:08 Lockdep warning after c0feea594e058223973db94c1c32a830c9807c86 sdf
@ 2022-10-13 16:45 ` Martin KaFai Lau
2022-10-13 20:39 ` Jakub Sitnicki
1 sibling, 0 replies; 5+ messages in thread
From: Martin KaFai Lau @ 2022-10-13 16:45 UTC (permalink / raw)
To: john.fastabend, jakub; +Cc: netdev, bpf, sdf
On 10/12/22 2:08 PM, sdf@google.com wrote:
> Hi John & Jakub,
>
> Upstream commit c0feea594e05 ("workqueue: don't skip lockdep work
> dependency in cancel_work_sync()") seems to trigger the following
> lockdep warning during test_prog's sockmap_listen:
>
> [ +0.003631] WARNING: possible circular locking dependency detected
> [ +0.003647] 6.0.0-dbx-DEV #10 Not tainted
> [ +0.002402] ------------------------------------------------------
> [ +0.003685] kworker/1:0/23 is trying to acquire lock:
> [ +0.003012] ffff888100b1e3f0 (sk_lock-AF_INET){+.+.}-{0:0}, at:
> tcp_sendpage+0x28/0x80
> [ +0.004655]
> but task is already holding lock:
> [ +0.003434] ffff88810642c360 (&psock->work_mutex){+.+.}-{3:3}, at:
> sk_psock_backlog+0x2e/0x370
> [ +0.005043]
> which lock already depends on the new lock.
>
> [ +0.004792]
> the existing dependency chain (in reverse order) is:
> [ +0.004397]
> -> #2 (&psock->work_mutex){+.+.}-{3:3}:
> [ +0.003732] __mutex_lock_common+0xdf/0xe70
> [ +0.002958] mutex_lock_nested+0x20/0x30
> [ +0.002685] sk_psock_backlog+0x2e/0x370
> [ +0.002689] process_one_work+0x22c/0x3b0
> [ +0.002815] worker_thread+0x21b/0x400
> [ +0.002652] kthread+0xf7/0x110
> [ +0.002406] ret_from_fork+0x1f/0x30
> [ +0.002512]
> -> #1 ((work_completion)(&psock->work)){+.+.}-{0:0}:
> [ +0.004457] __flush_work+0x6b/0xd0
> [ +0.002638] __cancel_work_timer+0x11a/0x1a0
> [ +0.002973] cancel_work_sync+0x10/0x20
> [ +0.002724] sk_psock_stop+0x298/0x2b0
> [ +0.002969] sock_map_close+0xd8/0x140
> [ +0.002739] inet_release+0x57/0x80
> [ +0.002475] sock_close+0x4b/0xe0
> [ +0.002380] __fput+0x101/0x230
> [ +0.002347] ____fput+0xe/0x10
> [ +0.002259] task_work_run+0x5d/0xb0
> [ +0.002535] exit_to_user_mode_loop+0xd6/0xf0
> [ +0.003019] exit_to_user_mode_prepare+0xa6/0x100
> [ +0.003201] syscall_exit_to_user_mode+0x5b/0x160
> [ +0.003145] do_syscall_64+0x49/0x80
> [ +0.002549] entry_SYSCALL_64_after_hwframe+0x63/0xcd
> [ +0.003410]
> -> #0 (sk_lock-AF_INET){+.+.}-{0:0}:
> [ +0.003906] __lock_acquire+0x16f4/0x30c0
> [ +0.002837] lock_acquire+0xc5/0x1c0
> [ +0.002599] lock_sock_nested+0x32/0x80
> [ +0.002690] tcp_sendpage+0x28/0x80
> [ +0.002435] inet_sendpage+0x7b/0xe0
> [ +0.002534] kernel_sendpage+0x5d/0xa0
> [ +0.002709] skb_send_sock+0x24b/0x2d0
> [ +0.002662] sk_psock_backlog+0x106/0x370
> [ +0.002908] process_one_work+0x22c/0x3b0
> [ +0.002736] worker_thread+0x21b/0x400
> [ +0.002552] kthread+0xf7/0x110
> [ +0.002252] ret_from_fork+0x1f/0x30
> [ +0.002480]
> other info that might help us debug this:
>
> [ +0.004778] Chain exists of:
> sk_lock-AF_INET --> (work_completion)(&psock->work) -->
> &psock->work_mutex
>
> [ +0.007265] Possible unsafe locking scenario:
>
> [ +0.003496] CPU0 CPU1
> [ +0.002717] ---- ----
> [ +0.002809] lock(&psock->work_mutex);
> [ +0.002335] lock((work_completion)(&psock->work));
> [ +0.004496] lock(&psock->work_mutex);
> [ +0.003766] lock(sk_lock-AF_INET);
> [ +0.002185]
> *** DEADLOCK ***
>
> [ +0.003600] 3 locks held by kworker/1:0/23:
> [ +0.002698] #0: ffff888100055138 ((wq_completion)events){+.+.}-{0:0}, at:
> process_one_work+0x1d6/0x3b0
> [ +0.005552] #1: ffffc900001e7e58
> ((work_completion)(&psock->work)){+.+.}-{0:0}, at: process_one_work+0x1fc/0x3b0
> [ +0.006085] #2: ffff88810642c360 (&psock->work_mutex){+.+.}-{3:3}, at:
> sk_psock_backlog+0x2e/0x370
> [ +0.005424]
> stack backtrace:
> [ +0.002689] CPU: 1 PID: 23 Comm: kworker/1:0 Not tainted 6.0.0-dbx-DEV #10
> [ +0.004086] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
> rel-1.16.0-0-gd239552ce722-prebuilt.qemu.org 04/01/2014
> [ +0.006806] Workqueue: events sk_psock_backlog
> [ +0.002699] Call Trace:
> [ +0.001577] <TASK>
> [ +0.001350] dump_stack_lvl+0x69/0xaa
> [ +0.002225] dump_stack+0x10/0x12
> [ +0.002051] print_circular_bug+0x289/0x290
> [ +0.002531] check_noncircular+0x12c/0x140
> [ +0.002578] __lock_acquire+0x16f4/0x30c0
> [ +0.002483] ? ret_from_fork+0x1f/0x30
> [ +0.002297] ? __this_cpu_preempt_check+0x13/0x20
> [ +0.002869] ? lock_is_held_type+0xf8/0x160
> [ +0.002511] lock_acquire+0xc5/0x1c0
> [ +0.002165] ? tcp_sendpage+0x28/0x80
> [ +0.002367] lock_sock_nested+0x32/0x80
> [ +0.002401] ? tcp_sendpage+0x28/0x80
> [ +0.002262] tcp_sendpage+0x28/0x80
> [ +0.002148] inet_sendpage+0x7b/0x[ 12.231432] sysrq: Power Off
> e0
> [ +0.002202[ 12.234545] kvm: exiting hardware virtualization
> ] kernel_sendpage+0x5d/0xa0
> [ +0.002277] skb_send_sock+0x24b/0x2d0
> [ +0.002278] ? _raw_spin_unlock_irqrestore+0x35/0x60
> [ +0.003030] ? __this_cpu_preempt_check+0x13/0x20
> [ +0.002861] ? lockdep_hardirqs_on+0x97/0x140
> [ +0.002685] ? trace_hardirqs_on+0x47/0x50
> [ +0.002576] ? _raw_spin_unlock_irqrestore+0x40/0x60
> [ +0.003207] sk_psock_backlog+0x106/0x370
> [ +0.002476] process_one_work+0x22c/0x3b0
> [ +0.002473] worker_thread+0x21b/0x400
> [ +0.002335] kthread+0xf7/0x110
> [ +0.001954] ? rcu_lock_release+0x20/0x20
> [ +0.002444] ? kthread_blkcg+0x30/0x30
> [ +0.002325] ret_from_fork+0x1f/0x30
> [ +0.002221] </TASK>
>
> This is on bpf-next:
>
> commit d31ada3b511141f4b78cae5a05cc2dad887c40b7 (HEAD -> bpf-next,
> bpf-next/master)
> Author: David Vernet <void@manifault.com>
> Date: Tue Oct 11 11:52:55 2022 -0500
>
> selftests/bpf: Alphabetize DENYLISTs
>
> Are you ware? Any idea what's wrong?
> Is there some stable fix I'm missing in bpf-next?
fwiw, CI has been hitting it pretty often also:
https://github.com/kernel-patches/bpf/actions/runs/3238290042/jobs/5306551130#step:6:5522
Unless bpf-next is missing some fixes, this needs to be addressed.
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: Lockdep warning after c0feea594e058223973db94c1c32a830c9807c86
2022-10-12 21:08 Lockdep warning after c0feea594e058223973db94c1c32a830c9807c86 sdf
2022-10-13 16:45 ` Martin KaFai Lau
@ 2022-10-13 20:39 ` Jakub Sitnicki
2022-10-16 18:11 ` Cong Wang
1 sibling, 1 reply; 5+ messages in thread
From: Jakub Sitnicki @ 2022-10-13 20:39 UTC (permalink / raw)
To: sdf; +Cc: john.fastabend, netdev, bpf, Cong Wang, Martin KaFai Lau
Hi Stan,
On Wed, Oct 12, 2022 at 02:08 PM -07, sdf@google.com wrote:
> Hi John & Jakub,
>
> Upstream commit c0feea594e05 ("workqueue: don't skip lockdep work
> dependency in cancel_work_sync()") seems to trigger the following
> lockdep warning during test_prog's sockmap_listen:
>
> [ +0.003631] WARNING: possible circular locking dependency detected
[...]
> Are you ware? Any idea what's wrong?
> Is there some stable fix I'm missing in bpf-next?
Thanks for bringing it up. I didn't know.
The mentioned commit doesn't look that fresh
commit c0feea594e058223973db94c1c32a830c9807c86
Author: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Date: Fri Jul 29 13:30:23 2022 +0900
workqueue: don't skip lockdep work dependency in cancel_work_sync()
... but then it just landed not so long ago, which explains things:
$ git describe --contains c0feea594e058223973db94c1c32a830c9807c86 --match 'v*'
v6.0-rc7~10^2
I've untangled the call chains leading to the potential dead-lock a
bit. There does seem to be a window of opportunity there.
psock->work.func = sk_psock_backlog()
ACQUIRE psock->work_mutex
sk_psock_handle_skb()
skb_send_sock()
__skb_send_sock()
sendpage_unlocked()
kernel_sendpage()
sock->ops->sendpage = inet_sendpage()
sk->sk_prot->sendpage = tcp_sendpage()
ACQUIRE sk->sk_lock
tcp_sendpage_locked()
RELEASE sk->sk_lock
RELEASE psock->work_mutex
sock_map_close()
ACQUIRE sk->sk_lock
sk_psock_stop()
sk_psock_clear_state(psock, SK_PSOCK_TX_ENABLED)
cancel_work_sync()
__cancel_work_timer()
__flush_work()
// wait for psock->work to finish
RELEASE sk->sk_lock
There is no fix I know of. Need to think. Ideas welcome.
CC Cong, just FYI, because we did rearrange the locking scheme in [1].
However it looks to me like the dead-lock was already there before that.
[1] https://lore.kernel.org/bpf/20210331023237.41094-5-xiyou.wangcong@gmail.com/
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: Lockdep warning after c0feea594e058223973db94c1c32a830c9807c86
2022-10-13 20:39 ` Jakub Sitnicki
@ 2022-10-16 18:11 ` Cong Wang
2022-10-24 9:36 ` Jakub Sitnicki
0 siblings, 1 reply; 5+ messages in thread
From: Cong Wang @ 2022-10-16 18:11 UTC (permalink / raw)
To: Jakub Sitnicki
Cc: sdf, john.fastabend, netdev, bpf, Cong Wang, Martin KaFai Lau
On Thu, Oct 13, 2022 at 10:39:08PM +0200, Jakub Sitnicki wrote:
> Hi Stan,
>
> On Wed, Oct 12, 2022 at 02:08 PM -07, sdf@google.com wrote:
> > Hi John & Jakub,
> >
> > Upstream commit c0feea594e05 ("workqueue: don't skip lockdep work
> > dependency in cancel_work_sync()") seems to trigger the following
> > lockdep warning during test_prog's sockmap_listen:
> >
> > [ +0.003631] WARNING: possible circular locking dependency detected
>
> [...]
>
> > Are you ware? Any idea what's wrong?
> > Is there some stable fix I'm missing in bpf-next?
>
> Thanks for bringing it up. I didn't know.
>
> The mentioned commit doesn't look that fresh
>
> commit c0feea594e058223973db94c1c32a830c9807c86
> Author: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
> Date: Fri Jul 29 13:30:23 2022 +0900
>
> workqueue: don't skip lockdep work dependency in cancel_work_sync()
>
> ... but then it just landed not so long ago, which explains things:
>
> $ git describe --contains c0feea594e058223973db94c1c32a830c9807c86 --match 'v*'
> v6.0-rc7~10^2
>
> I've untangled the call chains leading to the potential dead-lock a
> bit. There does seem to be a window of opportunity there.
>
> psock->work.func = sk_psock_backlog()
> ACQUIRE psock->work_mutex
> sk_psock_handle_skb()
> skb_send_sock()
> __skb_send_sock()
> sendpage_unlocked()
> kernel_sendpage()
> sock->ops->sendpage = inet_sendpage()
> sk->sk_prot->sendpage = tcp_sendpage()
> ACQUIRE sk->sk_lock
> tcp_sendpage_locked()
> RELEASE sk->sk_lock
> RELEASE psock->work_mutex
>
> sock_map_close()
> ACQUIRE sk->sk_lock
> sk_psock_stop()
> sk_psock_clear_state(psock, SK_PSOCK_TX_ENABLED)
> cancel_work_sync()
> __cancel_work_timer()
> __flush_work()
> // wait for psock->work to finish
> RELEASE sk->sk_lock
>
> There is no fix I know of. Need to think. Ideas welcome.
>
Thanks for the analysis.
I wonder if we can simply move this cancel_work_sync() out of sock
lock... Something like this:
diff --git a/include/linux/skmsg.h b/include/linux/skmsg.h
index 48f4b645193b..70d6cb94e580 100644
--- a/include/linux/skmsg.h
+++ b/include/linux/skmsg.h
@@ -376,7 +376,7 @@ static inline void sk_psock_report_error(struct sk_psock *psock, int err)
}
struct sk_psock *sk_psock_init(struct sock *sk, int node);
-void sk_psock_stop(struct sk_psock *psock, bool wait);
+void sk_psock_stop(struct sk_psock *psock);
#if IS_ENABLED(CONFIG_BPF_STREAM_PARSER)
int sk_psock_init_strp(struct sock *sk, struct sk_psock *psock);
diff --git a/net/core/skmsg.c b/net/core/skmsg.c
index ca70525621c7..ddc56660ce97 100644
--- a/net/core/skmsg.c
+++ b/net/core/skmsg.c
@@ -803,16 +803,13 @@ static void sk_psock_link_destroy(struct sk_psock *psock)
}
}
-void sk_psock_stop(struct sk_psock *psock, bool wait)
+void sk_psock_stop(struct sk_psock *psock)
{
spin_lock_bh(&psock->ingress_lock);
sk_psock_clear_state(psock, SK_PSOCK_TX_ENABLED);
sk_psock_cork_free(psock);
__sk_psock_zap_ingress(psock);
spin_unlock_bh(&psock->ingress_lock);
-
- if (wait)
- cancel_work_sync(&psock->work);
}
static void sk_psock_done_strp(struct sk_psock *psock);
@@ -850,7 +847,7 @@ void sk_psock_drop(struct sock *sk, struct sk_psock *psock)
sk_psock_stop_verdict(sk, psock);
write_unlock_bh(&sk->sk_callback_lock);
- sk_psock_stop(psock, false);
+ sk_psock_stop(psock);
INIT_RCU_WORK(&psock->rwork, sk_psock_destroy);
queue_rcu_work(system_wq, &psock->rwork);
diff --git a/net/core/sock_map.c b/net/core/sock_map.c
index a660baedd9e7..81beb16ab1eb 100644
--- a/net/core/sock_map.c
+++ b/net/core/sock_map.c
@@ -1596,7 +1596,7 @@ void sock_map_destroy(struct sock *sk)
saved_destroy = psock->saved_destroy;
sock_map_remove_links(sk, psock);
rcu_read_unlock();
- sk_psock_stop(psock, false);
+ sk_psock_stop(psock);
sk_psock_put(sk, psock);
saved_destroy(sk);
}
@@ -1619,9 +1619,10 @@ void sock_map_close(struct sock *sk, long timeout)
saved_close = psock->saved_close;
sock_map_remove_links(sk, psock);
rcu_read_unlock();
- sk_psock_stop(psock, true);
- sk_psock_put(sk, psock);
+ sk_psock_stop(psock);
release_sock(sk);
+ cancel_work_sync(&psock->work);
+ sk_psock_put(sk, psock);
saved_close(sk, timeout);
}
EXPORT_SYMBOL_GPL(sock_map_close);
^ permalink raw reply related [flat|nested] 5+ messages in thread
* Re: Lockdep warning after c0feea594e058223973db94c1c32a830c9807c86
2022-10-16 18:11 ` Cong Wang
@ 2022-10-24 9:36 ` Jakub Sitnicki
0 siblings, 0 replies; 5+ messages in thread
From: Jakub Sitnicki @ 2022-10-24 9:36 UTC (permalink / raw)
To: Cong Wang; +Cc: sdf, john.fastabend, netdev, bpf, Cong Wang, Martin KaFai Lau
On Sun, Oct 16, 2022 at 11:11 AM -07, Cong Wang wrote:
> On Thu, Oct 13, 2022 at 10:39:08PM +0200, Jakub Sitnicki wrote:
>> Hi Stan,
>>
>> On Wed, Oct 12, 2022 at 02:08 PM -07, sdf@google.com wrote:
>> > Hi John & Jakub,
>> >
>> > Upstream commit c0feea594e05 ("workqueue: don't skip lockdep work
>> > dependency in cancel_work_sync()") seems to trigger the following
>> > lockdep warning during test_prog's sockmap_listen:
>> >
>> > [ +0.003631] WARNING: possible circular locking dependency detected
>>
>> [...]
>>
>> > Are you ware? Any idea what's wrong?
>> > Is there some stable fix I'm missing in bpf-next?
>>
>> Thanks for bringing it up. I didn't know.
>>
>> The mentioned commit doesn't look that fresh
>>
>> commit c0feea594e058223973db94c1c32a830c9807c86
>> Author: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
>> Date: Fri Jul 29 13:30:23 2022 +0900
>>
>> workqueue: don't skip lockdep work dependency in cancel_work_sync()
>>
>> ... but then it just landed not so long ago, which explains things:
>>
>> $ git describe --contains c0feea594e058223973db94c1c32a830c9807c86 --match 'v*'
>> v6.0-rc7~10^2
>>
>> I've untangled the call chains leading to the potential dead-lock a
>> bit. There does seem to be a window of opportunity there.
>>
>> psock->work.func = sk_psock_backlog()
>> ACQUIRE psock->work_mutex
>> sk_psock_handle_skb()
>> skb_send_sock()
>> __skb_send_sock()
>> sendpage_unlocked()
>> kernel_sendpage()
>> sock->ops->sendpage = inet_sendpage()
>> sk->sk_prot->sendpage = tcp_sendpage()
>> ACQUIRE sk->sk_lock
>> tcp_sendpage_locked()
>> RELEASE sk->sk_lock
>> RELEASE psock->work_mutex
>>
>> sock_map_close()
>> ACQUIRE sk->sk_lock
>> sk_psock_stop()
>> sk_psock_clear_state(psock, SK_PSOCK_TX_ENABLED)
>> cancel_work_sync()
>> __cancel_work_timer()
>> __flush_work()
>> // wait for psock->work to finish
>> RELEASE sk->sk_lock
>>
>> There is no fix I know of. Need to think. Ideas welcome.
>>
>
> Thanks for the analysis.
>
> I wonder if we can simply move this cancel_work_sync() out of sock
> lock... Something like this:
[...]
> diff --git a/net/core/sock_map.c b/net/core/sock_map.c
> index a660baedd9e7..81beb16ab1eb 100644
> --- a/net/core/sock_map.c
> +++ b/net/core/sock_map.c
> @@ -1596,7 +1596,7 @@ void sock_map_destroy(struct sock *sk)
> saved_destroy = psock->saved_destroy;
> sock_map_remove_links(sk, psock);
> rcu_read_unlock();
> - sk_psock_stop(psock, false);
> + sk_psock_stop(psock);
> sk_psock_put(sk, psock);
> saved_destroy(sk);
> }
> @@ -1619,9 +1619,10 @@ void sock_map_close(struct sock *sk, long timeout)
> saved_close = psock->saved_close;
> sock_map_remove_links(sk, psock);
> rcu_read_unlock();
> - sk_psock_stop(psock, true);
> - sk_psock_put(sk, psock);
> + sk_psock_stop(psock);
> release_sock(sk);
> + cancel_work_sync(&psock->work);
> + sk_psock_put(sk, psock);
> saved_close(sk, timeout);
> }
> EXPORT_SYMBOL_GPL(sock_map_close);
Sorry for the delay. I've been out.
Great idea. I don't see why not.
^ permalink raw reply [flat|nested] 5+ messages in thread
end of thread, other threads:[~2022-10-24 9:39 UTC | newest]
Thread overview: 5+ messages (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
2022-10-12 21:08 Lockdep warning after c0feea594e058223973db94c1c32a830c9807c86 sdf
2022-10-13 16:45 ` Martin KaFai Lau
2022-10-13 20:39 ` Jakub Sitnicki
2022-10-16 18:11 ` Cong Wang
2022-10-24 9:36 ` Jakub Sitnicki
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