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Mon, 28 Sep 2026 23:09:45 -0700 (PDT) Content-Type: text/plain; charset=UTF-8 Date: Tue, 29 Sep 2026 06:09:44 +0000 Message-Id: Cc: , , , , , , , , , , , , Subject: Re: [PATCH bpf] bpf: Fix smp_processor_id() warning in rhtab_delete_elem() From: "Alexei Starovoitov" To: =?utf-8?q?=C3=96mer_Mete_Kaya?= , In-Reply-To: <20260928173703.504474-1-omermetekaya0@gmail.com> References: <20260928173703.504474-1-omermetekaya0@gmail.com> X-Mailer: mkdraft (claude review draft; edit before sending) Content-Transfer-Encoding: 8bit Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Mon, Sep 28, 2026 at 08:31 PM Ömer Mete Kaya wrote: > bpf_mem_cache_free_rcu() uses this_cpu_ptr() which requires preemption > to be disabled. In rhtab_delete_elem(), this call happens after > bpf_enable_instrumentation(), so preemption is re-enabled at that > point and this_cpu_ptr() triggers: bpf_disable_instrumentation() doesn't disable preemption. It's migrate_disable() plus bpf_prog_active++. bpf_mem_alloc relies on the callers to disable migration. See the comment above bpf_mem_alloc(). All callers of rhtab_delete_elem() do that except __rhtab_map_lookup_and_delete_batch(). That's the bug. bpf_disable_instrumentation() in rhtab_delete_elem() protects the bucket lock from NMI progs. rhtab_map_update_elem() calls bpf_mem_cache_alloc/free() outside of it too. Don't stretch it. Disable migration in the batch. > Fixes: 6905f8601298 ("bpf: Allow special fields in resizable hashtab") Wrong tag. The batch came in commit 818e00848227 ("bpf: Implement iteration ops for resizable hashtab") pw-bot: cr