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Date:   Tue, 21 Jul 2020 12:26:34 +0200
From:   Jakub Sitnicki <jakub@...udflare.com>
To:     Lorenzo Bianconi <lorenzo@...nel.org>
Cc:     netdev@...r.kernel.org, bpf@...r.kernel.org, davem@...emloft.net,
        ast@...nel.org, brouer@...hat.com, daniel@...earbox.net,
        lorenzo.bianconi@...hat.com, kuba@...nel.org
Subject: Re: [PATCH bpf-next] bpf: cpumap: fix possible rcpu kthread hung

On Sun, Jul 19, 2020 at 05:52 PM CEST, Lorenzo Bianconi wrote:
> Fix the following cpumap kthread hung. The issue is currently occurring
> when __cpu_map_load_bpf_program fails (e.g if the bpf prog has not
> BPF_XDP_CPUMAP as expected_attach_type)
>
> $./test_progs -n 101
> 101/1 cpumap_with_progs:OK
> 101 xdp_cpumap_attach:OK
> Summary: 1/1 PASSED, 0 SKIPPED, 0 FAILED
> [  369.996478] INFO: task cpumap/0/map:7:205 blocked for more than 122 seconds.
> [  369.998463]       Not tainted 5.8.0-rc4-01472-ge57892f50a07 #212
> [  370.000102] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> [  370.001918] cpumap/0/map:7  D    0   205      2 0x00004000
> [  370.003228] Call Trace:
> [  370.003930]  __schedule+0x5c7/0xf50
> [  370.004901]  ? io_schedule_timeout+0xb0/0xb0
> [  370.005934]  ? static_obj+0x31/0x80
> [  370.006788]  ? mark_held_locks+0x24/0x90
> [  370.007752]  ? cpu_map_bpf_prog_run_xdp+0x6c0/0x6c0
> [  370.008930]  schedule+0x6f/0x160
> [  370.009728]  schedule_preempt_disabled+0x14/0x20
> [  370.010829]  kthread+0x17b/0x240
> [  370.011433]  ? kthread_create_worker_on_cpu+0xd0/0xd0
> [  370.011944]  ret_from_fork+0x1f/0x30
> [  370.012348]
>                Showing all locks held in the system:
> [  370.013025] 1 lock held by khungtaskd/33:
> [  370.013432]  #0: ffffffff82b24720 (rcu_read_lock){....}-{1:2}, at: debug_show_all_locks+0x28/0x1c3
>
> [  370.014461] =============================================
>
> Fixes: 9216477449f3 ("bpf: cpumap: Add the possibility to attach an eBPF program to cpumap")
> Reported-by: Jakub Sitnicki <jakub@...udflare.com>
> Signed-off-by: Lorenzo Bianconi <lorenzo@...nel.org>
> ---

Tested-by: Jakub Sitnicki <jakub@...udflare.com>
Reviewed-by: Jakub Sitnicki <jakub@...udflare.com>

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