netdev - Re: [PATCH bpf-next 2/2] bpf: bring back removal of dev-bound id from idr

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Message-ID: <ZVvR_fu2TIe4Puii@google.com>
Date: Mon, 20 Nov 2023 13:39:09 -0800
From: Stanislav Fomichev <sdf@...gle.com>
To: bpf@...r.kernel.org, netdev@...r.kernel.org
Cc: ast@...nel.org, daniel@...earbox.net, andrii@...nel.org, 
	martin.lau@...ux.dev, song@...nel.org, yhs@...com, john.fastabend@...il.com, 
	kpsingh@...nel.org, haoluo@...gle.com, jolsa@...nel.org
Subject: Re: [PATCH bpf-next 2/2] bpf: bring back removal of dev-bound id from idr

On 11/13, Stanislav Fomichev wrote:
> Commit ef01f4e25c17 ("bpf: restore the ebpf program ID for BPF_AUDIT_UNLOAD
> and PERF_BPF_EVENT_PROG_UNLOAD") stopped removing program's id from
> idr when the offloaded/bound netdev goes away. I was supposed to
> take a look and check in [0], but apparently I did not.
> 
> The purpose of idr removal is to avoid BPF_PROG_GET_NEXT_ID returning
> stale ids for the programs that have a dead netdev. This functionality
> is verified by test_offload.py, but we don't run this test in the CI.
> 
> Introduce new bpf_prog_remove_from_idr which takes care of correctly
> dealing with potential double idr_remove() via separate skip_idr_remove
> flag in the aux.
> 
> Verified by running the test manually:
> test_offload.py: OK
> 
> 0: https://lore.kernel.org/all/CAKH8qBtyR20ZWAc11z1-6pGb3Hd47AQUTbE_cfoktG59TqaJ7Q@mail.gmail.com/
> 
> Fixes: ef01f4e25c17 ("bpf: restore the ebpf program ID for BPF_AUDIT_UNLOAD and PERF_BPF_EVENT_PROG_UNLOAD")
> Signed-off-by: Stanislav Fomichev <sdf@...gle.com>
> ---
>  include/linux/bpf.h  |  2 ++
>  kernel/bpf/offload.c |  3 +++
>  kernel/bpf/syscall.c | 15 +++++++++++----
>  3 files changed, 16 insertions(+), 4 deletions(-)
> 
> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index 4001d11be151..d2aa4b59bf1e 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -1414,6 +1414,7 @@ struct bpf_prog_aux {
>  	bool xdp_has_frags;
>  	bool exception_cb;
>  	bool exception_boundary;
> +	bool skip_idr_remove;
>  	/* BTF_KIND_FUNC_PROTO for valid attach_btf_id */
>  	const struct btf_type *attach_func_proto;
>  	/* function name for valid attach_btf_id */
> @@ -2049,6 +2050,7 @@ void bpf_prog_inc(struct bpf_prog *prog);
>  struct bpf_prog * __must_check bpf_prog_inc_not_zero(struct bpf_prog *prog);
>  void bpf_prog_put(struct bpf_prog *prog);
>  
> +void bpf_prog_remove_from_idr(struct bpf_prog *prog);
>  void bpf_prog_free_id(struct bpf_prog *prog);
>  void bpf_map_free_id(struct bpf_map *map);
>  
> diff --git a/kernel/bpf/offload.c b/kernel/bpf/offload.c
> index 1a4fec330eaa..6f4fe492ee2a 100644
> --- a/kernel/bpf/offload.c
> +++ b/kernel/bpf/offload.c
> @@ -112,6 +112,9 @@ static void __bpf_prog_offload_destroy(struct bpf_prog *prog)
>  	if (offload->dev_state)
>  		offload->offdev->ops->destroy(prog);
>  
> +	/* Make sure BPF_PROG_GET_NEXT_ID can't find this dead program */
> +	bpf_prog_remove_from_idr(prog);
> +
>  	list_del_init(&offload->offloads);
>  	kfree(offload);
>  	prog->aux->offload = NULL;
> diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
> index 0ed286b8a0f0..bc813e03e2cf 100644
> --- a/kernel/bpf/syscall.c
> +++ b/kernel/bpf/syscall.c
> @@ -2083,10 +2083,19 @@ static int bpf_prog_alloc_id(struct bpf_prog *prog)
>  	return id > 0 ? 0 : id;
>  }
>  
> -void bpf_prog_free_id(struct bpf_prog *prog)
> +void bpf_prog_remove_from_idr(struct bpf_prog *prog)
>  {
>  	unsigned long flags;
>  
> +	spin_lock_irqsave(&prog_idr_lock, flags);
> +	if (!prog->aux->skip_idr_remove)
> +		idr_remove(&prog_idr, prog->aux->id);
> +	prog->aux->skip_idr_remove = 1;
> +	spin_unlock_irqrestore(&prog_idr_lock, flags);
> +}
> +
> +void bpf_prog_free_id(struct bpf_prog *prog)
> +{
>  	/* cBPF to eBPF migrations are currently not in the idr store.
>  	 * Offloaded programs are removed from the store when their device
>  	 * disappears - even if someone grabs an fd to them they are unusable,
> @@ -2095,10 +2104,8 @@ void bpf_prog_free_id(struct bpf_prog *prog)
>  	if (!prog->aux->id)
>  		return;
>  
> -	spin_lock_irqsave(&prog_idr_lock, flags);
> -	idr_remove(&prog_idr, prog->aux->id);
> +	bpf_prog_remove_from_idr(prog);
>  	prog->aux->id = 0;
> -	spin_unlock_irqrestore(&prog_idr_lock, flags);
>  }
>  
>  static void __bpf_prog_put_rcu(struct rcu_head *rcu)
> -- 
> 2.42.0.869.gea05f2083d-goog
> 

Same here, should have been CC'ed to netdev.