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Thu, 22 Aug 2024 13:32:23 -0700 (PDT) Received: from [192.168.0.235] ([38.34.87.7]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-20385fcf6b3sm16545655ad.302.2024.08.22.13.32.22 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 22 Aug 2024 13:32:22 -0700 (PDT) Message-ID: Subject: Re: [PATCH v6 bpf-next 08/10] bpf: decouple stack_map_get_build_id_offset() from perf_callchain_entry From: Eduard Zingerman To: Andrii Nakryiko , bpf@vger.kernel.org Cc: linux-mm@kvack.org, akpm@linux-foundation.org, adobriyan@gmail.com, shakeel.butt@linux.dev, hannes@cmpxchg.org, ak@linux.intel.com, osandov@osandov.com, song@kernel.org, jannh@google.com, linux-fsdevel@vger.kernel.org, willy@infradead.org Date: Thu, 22 Aug 2024 13:32:17 -0700 In-Reply-To: <20240814185417.1171430-9-andrii@kernel.org> References: <20240814185417.1171430-1-andrii@kernel.org> <20240814185417.1171430-9-andrii@kernel.org> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.52.4 (3.52.4-1.fc40) MIME-Version: 1.0 X-Rspamd-Server: rspam03 X-Rspam-User: X-Rspamd-Queue-Id: 2E8F11C001B X-Stat-Signature: kd8n63hdktsyzjrq7stdz1osfqm431mn X-HE-Tag: 1724358744-199735 X-HE-Meta: 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 1jnXiZEG DiLHU2TXKdSl6epJ7Ksg5aOrdoDyLmJk1akfwmGnDDEZBPWIZT5wqvH0oEUbZCo9QiXFCpqmTPXD1u5A3clusmPIbgGb5wLlv/104a6LWTkguxDUxFVczYdjw0aR7aCBG/A2f2Mu94GexH4ftNcdZ1qi+a7pFRu+9SuTj8BOA8ID/8JaAB82siuBrcyrYaHkLaG9rZVHWIQ19CRGfPM+CQUNtDYYZqkDtmHZANn5umeRQewRLAxdl872MsJEj/VVVwm4wIfyqCF11rebl+oQ1LN64e3AYawBzEuFhA2wioa6Hlr4snlE4mdf3eFaoaLRV9iThwJdn96scNUQObLOvjYvjFXwNCFJpRDL9FZ0lQUqW5flS2kUYfDUo1EBmWtAmYarQO0pJitOD3pj8TttJK3+yPZZaDTd83j36pmZWztt26SUbSMWGRH7pRRDW4N/OqPQca2+LS0pVevSo5m7MViLF6w== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000019, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, 2024-08-14 at 11:54 -0700, Andrii Nakryiko wrote: > Change stack_map_get_build_id_offset() which is used to convert stack > trace IP addresses into build ID+offset pairs. Right now this function > accepts an array of u64s as an input, and uses array of > struct bpf_stack_build_id as an output. >=20 > This is problematic because u64 array is coming from > perf_callchain_entry, which is (non-sleepable) RCU protected, so once we > allows sleepable build ID fetching, this all breaks down. >=20 > But its actually pretty easy to make stack_map_get_build_id_offset() > works with array of struct bpf_stack_build_id as both input and output. > Which is what this patch is doing, eliminating the dependency on > perf_callchain_entry. We require caller to fill out > bpf_stack_build_id.ip fields (all other can be left uninitialized), and > update in place as we do build ID resolution. >=20 > We make sure to READ_ONCE() and cache locally current IP value as we > used it in a few places to find matching VMA and so on. Given this data > is directly accessible and modifiable by user's BPF code, we should make > sure to have a consistent view of it. >=20 > Signed-off-by: Andrii Nakryiko > --- Acked-by: Eduard Zingerman [...]