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From: Martin KaFai Lau <martin.lau@linux.dev>
To: Stanislav Fomichev <sdf@google.com>
Cc: ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org,
	song@kernel.org, yhs@fb.com, john.fastabend@gmail.com,
	kpsingh@kernel.org, haoluo@google.com, jolsa@kernel.org,
	David Ahern <dsahern@gmail.com>, Jakub Kicinski <kuba@kernel.org>,
	Willem de Bruijn <willemb@google.com>,
	Jesper Dangaard Brouer <brouer@redhat.com>,
	Anatoly Burakov <anatoly.burakov@intel.com>,
	Alexander Lobakin <alexandr.lobakin@intel.com>,
	Magnus Karlsson <magnus.karlsson@gmail.com>,
	Maryam Tahhan <mtahhan@redhat.com>,
	xdp-hints@xdp-project.net, netdev@vger.kernel.org,
	bpf@vger.kernel.org
Subject: [xdp-hints] Re: [PATCH bpf-next v3 03/12] bpf: XDP metadata RX kfuncs
Date: Thu, 8 Dec 2022 14:53:37 -0800	[thread overview]
Message-ID: <a5a636cc-5b03-686f-4be0-000383b05cfc@linux.dev> (raw)
In-Reply-To: <CAKH8qBvfNDo-+qB-CyvCjQAcTtftWoQJTPwVb4zdAMZs=TzG7w@mail.gmail.com>

On 12/8/22 11:07 AM, Stanislav Fomichev wrote:
>>> @@ -102,11 +112,25 @@ int bpf_prog_offload_init(struct bpf_prog *prog, union bpf_attr *attr)
>>>        if (err)
>>>                goto err_maybe_put;
>>>
>>> +     prog->aux->offload_requested = !(attr->prog_flags & BPF_F_XDP_HAS_METADATA);
>>> +
>>
>> If I read the set correctly, bpf prog can either use metadata kfunc or offload
>> but not both. It is fine to start with only supporting metadata kfunc when there
>> is no offload but will be useful to understand the reason. I assume an offloaded
>> bpf prog should still be able to call the bpf helpers like adjust_head/tail and
>> the same should go for any kfunc?
> 
> Yes, I'm assuming there should be some work on the offloaded device
> drivers to support metadata kfuncs.
> Offloaded kfuncs, in general, seem hard (how do we call kernel func
> from the device-offloaded prog?); so refusing kfuncs early for the
> offloaded case seems fair for now?

Ah, ok.  I was actually thinking the HW offloaded prog can just use the software 
ndo_* kfunc (like other bpf-helpers).  From skimming some 
bpf_prog_offload_ops:prepare implementation, I think you are right and it seems 
BPF_PSEUDO_KFUNC_CALL has not been recognized yet.

[ ... ]

>>> @@ -226,10 +263,17 @@ static void __bpf_prog_offload_destroy(struct bpf_prog *prog)
>>>
>>>    void bpf_prog_offload_destroy(struct bpf_prog *prog)
>>>    {
>>> +     struct net_device *netdev = NULL;
>>> +
>>>        down_write(&bpf_devs_lock);
>>> -     if (prog->aux->offload)
>>> +     if (prog->aux->offload) {
>>> +             netdev = prog->aux->offload->netdev;
>>>                __bpf_prog_offload_destroy(prog);
>>> +     }
>>>        up_write(&bpf_devs_lock);
>>> +
>>> +     if (netdev)
>>
>> May be I have missed a refcnt or lock somewhere.  Is it possible that netdev may
>> have been freed?
> 
> Yeah, with the offload framework, there are no refcnts. We put an
> "offloaded" device into a separate hashtable (protected by
> rtnl/semaphore).
> maybe_remove_bound_netdev will re-grab the locks (due to ordering:
> rtnl->bpf_devs_lock) and remove the device from the hashtable if it's
> still there.
> At least this is how, I think, it should work; LMK if something is
> still fishy here...
> 
> Or is the concern here that somebody might allocate new netdev reusing
> the same address? I think I have enough checks in
> maybe_remove_bound_netdev to guard against that. Or, at least, to make
> it safe :-)

Race is ok because ondev needs to be removed anyway when '!ondev->offdev && 
list_empty(&ondev->progs)'?  hmmm... tricky, please add a comment. :)

Why it cannot be done together in the bpf_devs_lock above?  The above cannot 
take an extra rtnl_lock before bpf_devs_lock?


  reply	other threads:[~2022-12-08 22:53 UTC|newest]

Thread overview: 61+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-12-06  2:45 [xdp-hints] [PATCH bpf-next v3 00/12] xdp: hints via kfuncs Stanislav Fomichev
2022-12-06  2:45 ` [xdp-hints] [PATCH bpf-next v3 01/12] bpf: Document XDP RX metadata Stanislav Fomichev
2022-12-08  4:25   ` [xdp-hints] " Jakub Kicinski
2022-12-08 19:06     ` Stanislav Fomichev
2022-12-06  2:45 ` [xdp-hints] [PATCH bpf-next v3 02/12] bpf: Rename bpf_{prog,map}_is_dev_bound to is_offloaded Stanislav Fomichev
2022-12-08  4:26   ` [xdp-hints] " Jakub Kicinski
2022-12-06  2:45 ` [xdp-hints] [PATCH bpf-next v3 03/12] bpf: XDP metadata RX kfuncs Stanislav Fomichev
2022-12-07  4:29   ` [xdp-hints] " Alexei Starovoitov
2022-12-07  4:52     ` Stanislav Fomichev
2022-12-07  7:23       ` Martin KaFai Lau
2022-12-07 18:05         ` Stanislav Fomichev
2022-12-08  2:47   ` Martin KaFai Lau
2022-12-08 19:07     ` Stanislav Fomichev
2022-12-08 22:53       ` Martin KaFai Lau [this message]
2022-12-08 23:45         ` Stanislav Fomichev
2022-12-08  5:00   ` Jakub Kicinski
2022-12-08 19:07     ` Stanislav Fomichev
2022-12-09  1:30       ` Jakub Kicinski
2022-12-09  2:57         ` Stanislav Fomichev
2022-12-08 22:39   ` Toke Høiland-Jørgensen
2022-12-08 23:46     ` Stanislav Fomichev
2022-12-09  0:07       ` Toke Høiland-Jørgensen
2022-12-09  2:57         ` Stanislav Fomichev
2022-12-10  0:42           ` Martin KaFai Lau
2022-12-10  1:12             ` Martin KaFai Lau
2022-12-09 11:10   ` Jesper Dangaard Brouer
2022-12-09 17:47     ` Stanislav Fomichev
2022-12-11 11:09       ` Jesper Dangaard Brouer
2022-12-06  2:45 ` [xdp-hints] [PATCH bpf-next v3 04/12] veth: Introduce veth_xdp_buff wrapper for xdp_buff Stanislav Fomichev
2022-12-06  2:45 ` [xdp-hints] [PATCH bpf-next v3 05/12] veth: Support RX XDP metadata Stanislav Fomichev
2022-12-06  2:45 ` [xdp-hints] [PATCH bpf-next v3 06/12] selftests/bpf: Verify xdp_metadata xdp->af_xdp path Stanislav Fomichev
2022-12-06  2:45 ` [xdp-hints] [PATCH bpf-next v3 07/12] mlx4: Introduce mlx4_xdp_buff wrapper for xdp_buff Stanislav Fomichev
2022-12-08  6:11   ` [xdp-hints] " Tariq Toukan
2022-12-08 19:07     ` Stanislav Fomichev
2022-12-06  2:45 ` [xdp-hints] [PATCH bpf-next v3 08/12] mxl4: Support RX XDP metadata Stanislav Fomichev
2022-12-08  6:09   ` [xdp-hints] " Tariq Toukan
2022-12-08 19:07     ` Stanislav Fomichev
2022-12-08 20:23       ` Tariq Toukan
2022-12-06  2:45 ` [xdp-hints] [PATCH bpf-next v3 09/12] xsk: Add cb area to struct xdp_buff_xsk Stanislav Fomichev
2022-12-06  2:45 ` [xdp-hints] [PATCH bpf-next v3 10/12] mlx5: Introduce mlx5_xdp_buff wrapper for xdp_buff Stanislav Fomichev
2022-12-06  2:45 ` [xdp-hints] [PATCH bpf-next v3 11/12] mlx5: Support RX XDP metadata Stanislav Fomichev
2022-12-08 22:59   ` [xdp-hints] " Toke Høiland-Jørgensen
2022-12-08 23:45     ` Stanislav Fomichev
2022-12-09  0:02       ` Toke Høiland-Jørgensen
2022-12-09  0:07         ` Alexei Starovoitov
2022-12-09  0:29           ` Toke Høiland-Jørgensen
2022-12-09  0:32             ` Alexei Starovoitov
2022-12-09  0:53               ` Toke Høiland-Jørgensen
2022-12-09  2:57                 ` Stanislav Fomichev
2022-12-09  5:24                   ` Saeed Mahameed
2022-12-09 12:59                     ` Jesper Dangaard Brouer
2022-12-09 14:37                       ` Toke Høiland-Jørgensen
2022-12-09 15:19                       ` Dave Taht
2022-12-09 14:42                   ` Toke Høiland-Jørgensen
2022-12-09 16:45                     ` Jakub Kicinski
2022-12-09 17:46                       ` Stanislav Fomichev
2022-12-09 22:13                         ` Jakub Kicinski
2022-12-06  2:45 ` [xdp-hints] [PATCH bpf-next v3 12/12] selftests/bpf: Simple program to dump XDP RX metadata Stanislav Fomichev
2022-12-08 22:28 ` [xdp-hints] Re: [PATCH bpf-next v3 00/12] xdp: hints via kfuncs Toke Høiland-Jørgensen
2022-12-08 23:47   ` Stanislav Fomichev
2022-12-09  0:14     ` Toke Høiland-Jørgensen

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