netdev - Re: [PATCH bpf] bpf: add schedule points in batch ops

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Date:   Thu, 17 Feb 2022 10:36:13 -0800
From:   sdf@...gle.com
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        "David S . Miller" <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>,
        Eric Dumazet <edumazet@...gle.com>, bpf <bpf@...r.kernel.org>,
        Brian Vazquez <brianvv@...gle.com>,
        syzbot <syzkaller@...glegroups.com>
Subject: Re: [PATCH bpf] bpf: add schedule points in batch ops

On 02/17, Eric Dumazet wrote:
> From: Eric Dumazet <edumazet@...gle.com>

> syzbot reported various soft lockups caused by bpf batch operations.

>   INFO: task kworker/1:1:27 blocked for more than 140 seconds.
>   INFO: task hung in rcu_barrier

> Nothing prevents batch ops to process huge amount of data,
> we need to add schedule points in them.

> Note that maybe_wait_bpf_programs(map) calls from
> generic_map_delete_batch() can be factorized by moving
> the call after the loop.

> This will be done later in -next tree once we get this fix merged,
> unless there is strong opinion doing this optimization sooner.

> Fixes: aa2e93b8e58e ("bpf: Add generic support for update and delete  
> batch ops")
> Fixes: cb4d03ab499d ("bpf: Add generic support for lookup batch op")
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Cc: Brian Vazquez <brianvv@...gle.com>
> Cc: Stanislav Fomichev <sdf@...gle.com>

Looks good, thank you!

Reviewed-by: Stanislav Fomichev <sdf@...gle.com>

> Reported-by: syzbot <syzkaller@...glegroups.com>
> ---
>   kernel/bpf/syscall.c | 3 +++
>   1 file changed, 3 insertions(+)

> diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
> index  
> fa4505f9b6119bcb219ab9733847a98da65d1b21..ca70fe6fba387937dfb54f10826f19ac55a8a8e7  
> 100644
> --- a/kernel/bpf/syscall.c
> +++ b/kernel/bpf/syscall.c
> @@ -1355,6 +1355,7 @@ int generic_map_delete_batch(struct bpf_map *map,
>   		maybe_wait_bpf_programs(map);
>   		if (err)
>   			break;
> +		cond_resched();
>   	}
>   	if (copy_to_user(&uattr->batch.count, &cp, sizeof(cp)))
>   		err = -EFAULT;
> @@ -1412,6 +1413,7 @@ int generic_map_update_batch(struct bpf_map *map,

>   		if (err)
>   			break;
> +		cond_resched();
>   	}

>   	if (copy_to_user(&uattr->batch.count, &cp, sizeof(cp)))
> @@ -1509,6 +1511,7 @@ int generic_map_lookup_batch(struct bpf_map *map,
>   		swap(prev_key, key);
>   		retry = MAP_LOOKUP_RETRIES;
>   		cp++;
> +		cond_resched();
>   	}

>   	if (err == -EFAULT)
> --
> 2.35.1.265.g69c8d7142f-goog