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Wed, 23 Sep 2026 16:04:04 -0700 (PDT) Content-Type: text/plain; charset=UTF-8 Date: Wed, 23 Sep 2026 23:04:03 +0000 Message-Id: From: "Alexei Starovoitov" To: "Yun Lu" , , , , , , , , , , Cc: , Subject: Re: [PATCH bpf-next v3 1/2] bpf: Fix task work scheduling and callback race In-Reply-To: <20260922100042.136818-2-luyun_611@163.com> References: <20260922100042.136818-1-luyun_611@163.com> <20260922100042.136818-2-luyun_611@163.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 Tue, Sep 22, 2026 at 06:00 PM Yun Lu wrote: > - err = task_work_add(ctx->task, &ctx->work, ctx->mode); > + task = get_task_struct(ctx->task); > + err = task_work_add(task, &ctx->work, ctx->mode); Why? There should be no need for get_task_struct(). rcu_read_lock() keeps task_struct around. bpf_task_release() is put_task_struct_rcu_user(), so the task is freed after rcu gp and guard(rcu)() covers the whole handler. task = ctx->task; is enough. The commit log still says that rcu_read_lock() "does not retain ctx->task". why? [...] > + if (unlikely(irq_work_is_busy(&ctx->irq_work))) { > + (void)cmpxchg(&ctx->state, BPF_TW_PENDING, BPF_TW_STANDBY); > + bpf_task_work_ctx_put(ctx); > + return ERR_PTR(-EBUSY); > + } This is a fix for a different bug. Pls split it into a separate patch and describe the sequence in its commit log the way it's done for the first one. "publishing a false SCHEDULED state" doesn't say what breaks. pw-bot: cr