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AJvYcCX0Fnhh234lpG1d1IFLySWpAOgOcvhoRAf0nzw6AOU+yVNgm0HocvptXN6YS688myT6SGs=@vger.kernel.org X-Gm-Message-State: AOJu0YzoBDt0BcUV1Dis7y3mSt4IFyPG9/TNo39/1VZwe6DmnrohTdb3 X/YogVGeoynn2f0iKKtNxuI/9SMErxmdRp88PYwNe/TU1rgphmyc X-Google-Smtp-Source: AGHT+IEr8Fd58V85LgqUekTOkg+lwcTw6phJX+JcNdm7qaq0XuP7MTgY19fzPTgm1sP/jFvpNbsFcA== X-Received: by 2002:a17:90b:1650:b0:2d8:7a63:f9c8 with SMTP id 98e67ed59e1d1-2e15a3105eamr4239201a91.14.1727781253141; Tue, 01 Oct 2024 04:14:13 -0700 (PDT) Received: from [192.168.0.235] ([38.34.87.7]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-2e0b6c9fa91sm9897961a91.29.2024.10.01.04.14.12 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 01 Oct 2024 04:14:12 -0700 (PDT) Message-ID: <1ea99d1e31c3f52f8962b186a150dfb0ffd23e45.camel@gmail.com> Subject: Re: [PATCH bpf-next v4 0/4] bpf: Fix tailcall infinite loop caused by freplace From: Eduard Zingerman To: Leon Hwang , bpf@vger.kernel.org Cc: ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org, toke@redhat.com, martin.lau@kernel.org, yonghong.song@linux.dev, puranjay@kernel.org, xukuohai@huaweicloud.com, iii@linux.ibm.com, kernel-patches-bot@fb.com Date: Tue, 01 Oct 2024 04:14:08 -0700 In-Reply-To: <20240929132757.79826-1-leon.hwang@linux.dev> References: <20240929132757.79826-1-leon.hwang@linux.dev> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.52.4 (3.52.4-1.fc40) Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Sun, 2024-09-29 at 21:27 +0800, Leon Hwang wrote: > Previously, I fixed a tailcall infinite loop issue caused by trampoline[0= ]. >=20 > At this time, I fix a tailcall infinite loop issue caused by tailcall and > freplace combination by preventing updating extended prog to prog_array m= ap > and preventing extending tail callee prog with freplace: >=20 > 1. If a prog or its subprog has been extended by freplace prog, the prog > can not be updated to prog_array map. > 2. If a prog has been updated to prog_array map, it or its subprog can no= t > be extended by freplace prog. So, once this series is applied we essentially have: - three variables: - tgt_prog->aux->is_extended - tgt_prog->aux->prog_array_member_cnt - trampoline->extension_prog - four operations: - link/attach extension program 'prog' using trampoline 'tr' - unlink/detach extension program 'prog' using trampoline 'tr' - put program 'tgt_prog' into prog array - remove program 'tgt_prog' from prog array And above four operations have the following pseudo-code with regards to update of the variables: - link/attach extension program 'prog' using trampoline 'tr': with lock(tgt_prog->ext_mutex): if tgt_prog->aux->prog_array_member_cnt: return error if tr->extension_prog: return error tr->extension_prog =3D prog tgt_prog->is_extended =3D true - unlink/detach extension program 'prog' using trampoline 'tr': with lock(tgt_prog->ext_mutex): tr->extension_prog =3D NULL tgt_prog->is_extended =3D false - put program 'tgt_prog' into prog array: with lock(tgt_prog->ext_mutex): if tgt_prog->aux->is_extended: return error tgt_prog->aux->prog_array_member_cnt++ - remove program 'tgt_prog' from prog array: with lock(tgt_prog->ext_mutex): tgt_prog->aux->prog_array_member_cnt-- I think this is correct, would be great if someone with more concurrency related experience would take a look. 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