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Sat, 31 Oct 2026 10:10:08 -0700 (PDT) Received: from localhost ([153.61.198.255]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-3ae845df666sm8093713a91.14.2026.10.31.10.10.07 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sat, 31 Oct 2026 10:10:08 -0700 (PDT) Content-Type: text/plain; charset=UTF-8 Date: Sat, 31 Oct 2026 17:10:07 +0000 Message-Id: Cc: , , , , , , , , , , , , , , , , , , , , , , Subject: Re: [PATCH bpf-next 11/13] bpf: keep module BTF until the vmlinux BTF is parsed From: "Alexei Starovoitov" To: , , , , , , In-Reply-To: References: <20261031130959.23472-12-wanjay@amazon.com> Content-Transfer-Encoding: 8bit X-Mailing-List: linux-trace-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 On Sat, Oct 31, 2026 at 06:55 AM bot+bpf-ci@kernel.org wrote: >> +/* Undo btf_parse_kept_modules() of a round that is not published */ >> +static void btf_unparse_kept_modules(void) >> +{ > [ ... ] >> + btf_mod->btf->data = NULL; /* the kept copy */ >> + btf_put(btf_mod->btf); >> + btf_mod->btf = NULL; >> + } >> +} [...] > Can a module BTF that is rolled back by btf_unparse_kept_modules() still be > reachable through btf_idr? Yes. It's real. The NULL deref in the inline BTF is real too. This is quite heavy. As you can see both bots poked plenty of holes. Five of them are in the -ENOMEM rollback of patches 10 and 11: where what goes wrong --------------------------- ------------------------------------------- btf_get_fd_by_id() takes a ref on a BTF that is rolled back btf_free_rcu() reads btf_mod->data that rmmod freed btf_parse_kept_modules() -ENOMEM in the inline BTF removes its file bpf_struct_ops_desc_init() -ENOMEM of ->init() becomes -EINVAL btf_vmlinux_data() -ENOMEM without btf_zst repeats forever The rollback exists because vmalloc() gives up when the task is killed. can we run the parse from a work item, schedule_work() + flush_work() ? A kworker gets no signals, so -ENOMEM can be final, like without the option. Every parse then ends in smp_store_release(&btf_vmlinux), and btf_get_fd_by_id() sleeps on btf_vmlinux_lock until that. Then no need for the retry, btf_unparse_kept_modules(), the 2nd call of ->init(), etc. See my other reply. pw-bot: cr