From nobody Wed Apr 1 10:27:12 2026 Received: from mail-wm1-f74.google.com (mail-wm1-f74.google.com [209.85.128.74]) (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 9936E37F758 for ; Wed, 1 Apr 2026 04:52:21 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.128.74 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775019143; cv=none; b=f5w636nlts/dCBtRoZMItgXZ1G+RNxZYpKrDWgrcySYaOHmZ00cHZWb4vCZKlOC/zfLuDUAxsrRgDKJNAc/ITQ9rKd7/XPb0WzFoQmtXwCaaLa0CuEZEmfkODhpMcL+dKoZYIumPDnd220yuzz1K9mSxAjApA/qNrhFURhyKrhg= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775019143; c=relaxed/simple; bh=IIW5MGp1erBt6CogygoK15lk/eSdIFNLr1/sdWWPNc4=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=PKY4hMKfKZzKwcRATDMqYLdZs80uCiNoKpQJtANnlAmK4Fj2OQHLcQ+Jo370OypqFNH/xPk1r54bFWjo5Iwdvn0GB1CxSk092/XMbzgnbzKox6U3fOexz+rT7+6RPCz1pIytiRAWLirm0kyklgl8aqK9YD2JdQKdD7rwGW6ZWdE= 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=GfOkbqPR; arc=none smtp.client-ip=209.85.128.74 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="GfOkbqPR" Received: by mail-wm1-f74.google.com with SMTP id 5b1f17b1804b1-4839fc4cef6so4412575e9.0 for ; Tue, 31 Mar 2026 21:52:21 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20251104; t=1775019140; x=1775623940; 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=AK7C9g36qtD1NdTgAM1Qfb35mHUC8CgKZhIzjTXpWYU=; b=GfOkbqPR+DXANHT8HDdZfvXPRcaYwKQYrIqODehdl5B2RjhMpWL/AW2EyGeiepjIPd KVy5IYiVhA8rsIs1HXcHHvbroWi56GGoHKxEooL7Cmi+yVu3phW4sTa+MYn/MoOsOXcK 9SkyD5Pi0TGPu4bDecc/MAHaMzc5IdhoMqEghZ13FMBSQU/feDRTrfw4lMObMSANpyFR RSrvP0OGPA3DvkxUJyof7oOwJVUBIZLyMXalpL0K0KHOTHVgadgdAN0vQcfZci+lr8HO HQcJfncjvI4/z54xvH5c010RjvwklJW9/r5bUfKcM7syMlO8QHoKEJ2p9v7MUtOd1pYO h0XA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1775019140; x=1775623940; 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=AK7C9g36qtD1NdTgAM1Qfb35mHUC8CgKZhIzjTXpWYU=; b=iyjhnhmjPKECh3LtDh0v44nxuGcQkW6SJfil90R11l2GnbLRSYLMaqPsvVCNLRZN42 TRQlyAisS0KRw0xVLN2bVig3O7zZ6qLumaHcj51mKHyb48HnJS/Rkqqa+umKo5DGpq6E GDpNPeyweMnfhwU1WC3Cm9zkeUnTcg5Conx9IWZzcq8bESYpJJ0l/ArckoE5U2l4v5JK imstO78AjSXIilhGjV5CU6wU9zVhkrecDqWUbDQCpOMJD/H8AnInSiVOBz4UmKXh+wkt BmzM7rbCkfuXrKhDUH0vAAjhn3H74Wz7O5Am+W2L3qksCZIzuV58DbfWyhAtHlCl+Znq pGrw== X-Forwarded-Encrypted: i=1; AJvYcCUG+1n1FddBLPreygipaR8jITwVZNgeG8uTkk/6mRCojUJadibb6PW9eWb6Upa8WHPzVOdFe1xKhRZffDo=@vger.kernel.org X-Gm-Message-State: AOJu0YxNf8fS3tfge/mGIogn3WWcpb3aBVGEt/oaMXNhF3oDUi3wCmM9 FIx9Rm09JLREpgVImjeCuwIYsqt7azryv3BfTDCHjvhr59jczYxJfkAL/veqkwUYwpQ3xhbDHol QC7s4c+UUJ5oi+UZ16Lk9HQ== X-Received: from wmoq6.prod.google.com ([2002:a05:600c:46c6:b0:486:fbd8:2af6]) (user=vdonnefort job=prod-delivery.src-stubby-dispatcher) by 2002:a05:600c:c04a:b0:485:fbd2:f72 with SMTP id 5b1f17b1804b1-4888356610dmr23580735e9.1.1775019139978; Tue, 31 Mar 2026 21:52:19 -0700 (PDT) Date: Wed, 1 Apr 2026 05:50:59 +0100 In-Reply-To: <20260401045100.3394299-1-vdonnefort@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20260401045100.3394299-1-vdonnefort@google.com> X-Mailer: git-send-email 2.53.0.1118.gaef5881109-goog Message-ID: <20260401045100.3394299-2-vdonnefort@google.com> Subject: [PATCH v2 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..d6c3f94d67cd 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) { @@ -361,6 +373,7 @@ static struct trace_remote_iterator =20 switch (type) { case TRI_CONSUMING: + ring_buffer_poll_remote(remote->trace_buffer, cpu); INIT_DELAYED_WORK(&iter->poll_work, __poll_remote); schedule_delayed_work(&iter->poll_work, msecs_to_jiffies(remote->poll_m= s)); break; @@ -476,6 +489,9 @@ __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