netdev - Re: faom 13cc1d4ee0a231f81951ee87f1e55229907966ee Mon Sep 17 00:00:00 2001

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Message-ID: <f516ac54-058b-1b7d-ab21-8405e1fe77fa@huaweicloud.com>
Date: Mon, 6 Jan 2025 16:18:34 +0800
From: Hou Tao <houtao@...weicloud.com>
To: bpf@...r.kernel.org, netdev@...r.kernel.org
Cc: Martin KaFai Lau <martin.lau@...ux.dev>,
 Alexei Starovoitov <alexei.starovoitov@...il.com>,
 Andrii Nakryiko <andrii@...nel.org>, Eduard Zingerman <eddyz87@...il.com>,
 Song Liu <song@...nel.org>, Hao Luo <haoluo@...gle.com>,
 Yonghong Song <yonghong.song@...ux.dev>,
 Daniel Borkmann <daniel@...earbox.net>, KP Singh <kpsingh@...nel.org>,
 Stanislav Fomichev <sdf@...ichev.me>, Jiri Olsa <jolsa@...nel.org>,
 John Fastabend <john.fastabend@...il.com>, xukuohai@...wei.com,
 "houtao1@...wei.com" <houtao1@...wei.com>
Subject: Re: faom 13cc1d4ee0a231f81951ee87f1e55229907966ee Mon Sep 17 00:00:00
 2001

Hi,

The header of patch #0 is broken for the patch set. However, it seems
BPF CI still can handle it and the content of patch #0 is still intact,
so I will not resend the patch set and instead I will respin it after
receiving some comments. Sorry for the inconvenience.

On 1/6/2025 4:18 PM, Hou Tao wrote:
> Hi,
>
> The use of migrate_{disable|enable} pair in BPF is mainly due to the
> introduction of bpf memory allocator and the use of per-CPU data struct
> in its internal implementation. The caller needs to disable migration
> before invoking the alloc or free APIs of bpf memory allocator, and
> enable migration after the invocation.
>
> The main users of bpf memory allocator are various kind of bpf maps in
> which the map values or the special fields in the map values are
> allocated by using bpf memory allocator.
>
> At present, the running context for bpf program has already disabled
> migration explictly or implictly, therefore, when these maps are
> manipulated in bpf program, it is OK to not invoke migrate_disable()
> and migrate_enable() pair. Howevers, it is not always the case when
> these maps are manipulated through bpf syscall, therefore many
> migrate_{disable|enable} pairs are added when the map can either be
> manipulated by BPF program or BPF syscall.
>
> The initial idea of reducing the use of migrate_{disable|enable} comes
> from Alexei [1]. I turned it into a patch set that archives the goals
> through the following three methods:
>
> 1. remove unnecessary migrate_{disable|enable} pair
> when the BPF syscall path also disables migration, it is OK to remove
> the pair. Patch #1~#3 fall into this category, while patch #4~#5 are
> partially included.
>
> 2. move the migrate_{disable|enable} pair from inner callee to outer
>    caller
> Instead of invoking migrate_disable() in the inner callee, invoking
> migrate_disable() in the outer caller to simplify reasoning about when
> migrate_disable() is needed. Patch #4~#5 and patch #6~#19 belongs to
> this category.
>
> 3. add cant_migrate() check in the inner callee
> Add cant_migrate() check in the inner callee to ensure the guarantee
> that migration is disabled is not broken. Patch #1~#5, #13, #16~#19 also
> belong to this category.
>
> Considering the bpf-next CI is broken, the patch set is verified by
> using bpf tree. Please check the individual patches for more details.
> Comments are always welcome.
>
> [1]: https://lore.kernel.org/bpf/CAADnVQKZ3=F0L7_R_pYqu7ePzpXRwQEN8tCzmFoxjdJHamMOUQ@mail.gmail.com
>
> Hou Tao (19):
>   bpf: Remove migrate_{disable|enable} from LPM trie
>   bpf: Remove migrate_{disable|enable} in ->map_for_each_callback
>   bpf: Remove migrate_{disable|enable} in htab_elem_free
>   bpf: Remove migrate_{disable|enable} from bpf_cgrp_storage_lock
>     helpers
>   bpf: Remove migrate_{disable|enable} from bpf_task_storage_lock
>     helpers
>   bpf: Disable migration when destroying inode storage
>   bpf: Disable migration when destroying sock storage
>   bpf: Disable migration when cloning sock storage
>   bpf: Disable migration in bpf_selem_free_rcu
>   bpf: Disable migration in array_map_free()
>   bpf: Disable migration in htab_map_free()
>   bpf: Disable migration for bpf_selem_unlink in
>     bpf_local_storage_map_free()
>   bpf: Remove migrate_{disable|enable} in bpf_obj_free_fields()
>   bpf: Remove migrate_{disable,enable} in bpf_cpumask_release()
>   bpf: Disable migration before calling ops->map_free()
>   bpf: Remove migrate_{disable|enable} from bpf_selem_alloc()
>   bpf: Remove migrate_{disable|enable} from bpf_local_storage_alloc()
>   bpf: Remove migrate_{disable|enable} from bpf_local_storage_free()
>   bpf: Remove migrate_{disable|enable} from bpf_selem_free()
>
>  kernel/bpf/arraymap.c          |  6 ++----
>  kernel/bpf/bpf_cgrp_storage.c  | 15 +++++++-------
>  kernel/bpf/bpf_inode_storage.c |  9 ++++----
>  kernel/bpf/bpf_local_storage.c | 38 +++++++++++++++-------------------
>  kernel/bpf/bpf_task_storage.c  | 15 +++++++-------
>  kernel/bpf/cpumask.c           |  2 --
>  kernel/bpf/hashtab.c           | 21 ++++++++-----------
>  kernel/bpf/helpers.c           |  4 ----
>  kernel/bpf/lpm_trie.c          | 24 +++++++--------------
>  kernel/bpf/range_tree.c        |  2 --
>  kernel/bpf/syscall.c           | 12 ++++++++---
>  net/core/bpf_sk_storage.c      | 11 ++++++----
>  12 files changed, 71 insertions(+), 88 deletions(-)
>