From nobody Wed Apr 1 10:28:48 2026 Received: from mail-wm1-f73.google.com (mail-wm1-f73.google.com [209.85.128.73]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id A3F6635B138 for ; Wed, 1 Apr 2026 02:51:56 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.128.73 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775011922; cv=none; b=GYta6sxqP9alGcBuCvwN2tzNsvsjnQn4AjwS+EYNcebFz+x/5ZL0ITKje/XlDJerdH09rRbzWHkf3CotOtVGQGezQoNaMLV+ap6mKPH+9fo4/2fJAqVlZDSg2gV8HZPUtMzIHY5uGMXUAUJp4wSG2xPZLwNslGfCtAa/gvKoMIA= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775011922; c=relaxed/simple; bh=Xrq4aUL1JXkGE55doELayakGSYFvldPCKQqMYlmSfgE=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=cgzaQgEV/KvKUrwFn2NAu4rEUJWurAZATv9sNNIr8G/HkyU0n3lqRLlLBfEUc5klwoNHhyKy8+G8sh3nITm9liU/7GddEDDSzIrc/IAP7dzedcwfyJMytcKqo5Ywo/ZjBR3SckhE9M6ZpH2O3qLywQEimsLC2AgQw+4LFtdWdnw= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=flex--vdonnefort.bounces.google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=X3vzetFv; arc=none smtp.client-ip=209.85.128.73 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=flex--vdonnefort.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="X3vzetFv" Received: by mail-wm1-f73.google.com with SMTP id 5b1f17b1804b1-486fa07f2bbso39685135e9.2 for ; Tue, 31 Mar 2026 19:51:56 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20251104; t=1775011914; x=1775616714; darn=vger.kernel.org; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:from:to:cc:subject:date:message-id:reply-to; bh=Eca4DbOW8XwXrqOV4vR/pp7c+WdGwg7Dl0/8lIXWnzc=; b=X3vzetFvus37+1WAhyXaIuY8EtRRAdKlqHXIltzJ/mdCWiNHSds9zEI5Sz0MIAqU6J UvlTO3ugl1/jPOUC18oNtKYzpf7ep0V8r9g20EmT7bgPK2IOmDHPkI1DEe+ijeBtbdEP o+FafTT3nAdSN95u+m0lIl0zj95t81RQ48ZCxzNSJJ1r3H+waNWskLaSyfPRzhDQvMR9 BN99zrGrGCR2Lh/qwjeeDoAd8DFgRA4RqmNui+PdXkAkw1MJp7hQnLUvB5/ChtSBAiHq pk6tQK9JnFq163ORvTClEX6bhabC82SxNl/p3E18PaC4YhMO9VlhvWVwrmp5I08Y/N3/ welg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1775011914; x=1775616714; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=Eca4DbOW8XwXrqOV4vR/pp7c+WdGwg7Dl0/8lIXWnzc=; b=X10IzIgjvX6TbvW7d8grdh4Uo9TvHUqSmUS0SKxuPHlSmvUNmrrP4xJmJVDUxVdFun 3qGkUY1YzrusQcXK3PQmKWBRds4yNKN3Wj/4gNYefQ5AFeKXA43lsQ5J4pycXZdk5NOX PULmJFPpYSSVff6qooGeZQvG/0EBVnujuWgwlfsOtNoJvVSwRMSVt/l8YpSPDGHXbyxE iASPg5vvhq6CIiEvzk0tJEIoJInlSiIRPjKryVk4HA2mbIVt/omNunrqpAqUxXYg0dh0 AlHsa/bgJoiabjRH1Icv/7/jVWMw2UpZwfbyr8+GfGAbPvq6QofKBs76scyUHqQFd2OY lMaw== X-Forwarded-Encrypted: i=1; AJvYcCWYhzBIvhaYbl73qSCUgP36aUwiwEydMbBB853mp+R792SgD24wufrdXs3+QKTfYXs7BwcVF6tuC7nnQhE=@vger.kernel.org X-Gm-Message-State: AOJu0YyUKUBzT3xozponNqAMibTLPyOQU0jyZcQeRAYEgTTiW+KHDgqo GeVTBm0haJbYyrVJ2/kgIFT6sv0a7FqzAMmBDX7OXfNJaoTnuuIvQnECcLMJF/jMpqy93mhmQEp DK90xDKhITFTkjp45CJr49w== X-Received: from wmow3.prod.google.com ([2002:a05:600c:4743:b0:485:2ef1:a59b]) (user=vdonnefort job=prod-delivery.src-stubby-dispatcher) by 2002:a05:600d:8:b0:486:ffa3:594 with SMTP id 5b1f17b1804b1-488835b760amr22907075e9.23.1775011914540; Tue, 31 Mar 2026 19:51:54 -0700 (PDT) Date: Wed, 1 Apr 2026 03:50:02 +0100 In-Reply-To: <20260401025003.3258729-1-vdonnefort@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20260401025003.3258729-1-vdonnefort@google.com> X-Mailer: git-send-email 2.53.0.1118.gaef5881109-goog Message-ID: <20260401025003.3258729-2-vdonnefort@google.com> Subject: [PATCH 1/2] tracing: Non-consuming read for trace remotes with an offline CPU From: Vincent Donnefort To: rostedt@goodmis.org, mhiramat@kernel.org, mathieu.desnoyers@efficios.com, linux-trace-kernel@vger.kernel.org, maz@kernel.org Cc: kernel-team@android.com, linux-kernel@vger.kernel.org, Vincent Donnefort Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" When a trace_buffer is created while a CPU is offline, this CPU is cleared from the trace_buffer CPU mask, preventing the creation of a non-consuming iterator (ring_buffer_iter). For trace remotes, it means the iterator fails to be allocated (-ENOMEM) even though there are available ring buffers in the trace_buffer. For non-consuming reads of trace remotes, skip missing ring_buffer_iter to allow reading the available ring buffers. Signed-off-by: Vincent Donnefort diff --git a/kernel/trace/trace_remote.c b/kernel/trace/trace_remote.c index 0d78e5f5fe98..39d5414c1723 100644 --- a/kernel/trace/trace_remote.c +++ b/kernel/trace/trace_remote.c @@ -282,6 +282,14 @@ static void trace_remote_put(struct trace_remote *remo= te) trace_remote_try_unload(remote); } =20 +static bool trace_remote_has_cpu(struct trace_remote *remote, int cpu) +{ + if (cpu =3D=3D RING_BUFFER_ALL_CPUS) + return true; + + return ring_buffer_poll_remote(remote->trace_buffer, cpu) =3D=3D 0; +} + static void __poll_remote(struct work_struct *work) { struct delayed_work *dwork =3D to_delayed_work(work); @@ -324,6 +332,10 @@ static int __alloc_ring_buffer_iter(struct trace_remot= e_iterator *iter, int cpu) iter->rb_iters[cpu] =3D ring_buffer_read_start(iter->remote->trace_buffe= r, cpu, GFP_KERNEL); if (!iter->rb_iters[cpu]) { + /* This CPU isn't part of trace_buffer. Skip it */ + if (!trace_remote_has_cpu(iter->remote, cpu)) + continue; + __free_ring_buffer_iter(iter, RING_BUFFER_ALL_CPUS); return -ENOMEM; } @@ -347,10 +359,10 @@ static struct trace_remote_iterator if (ret) return ERR_PTR(ret); =20 - /* Test the CPU */ - ret =3D ring_buffer_poll_remote(remote->trace_buffer, cpu); - if (ret) + if (!trace_remote_has_cpu(remote, cpu)) { + ret =3D -ENODEV; goto err; + } =20 iter =3D kzalloc_obj(*iter); if (iter) { @@ -476,6 +488,9 @@ __peek_event(struct trace_remote_iterator *iter, int cp= u, u64 *ts, unsigned long return ring_buffer_peek(iter->remote->trace_buffer, cpu, ts, lost_events= ); case TRI_NONCONSUMING: rb_iter =3D __get_rb_iter(iter, cpu); + if (!rb_iter) + return NULL; + rb_evt =3D ring_buffer_iter_peek(rb_iter, ts); if (!rb_evt) return NULL; --=20 2.53.0.1118.gaef5881109-goog