From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-wm1-f69.google.com (mail-wm1-f69.google.com [209.85.128.69]) (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 7759749E5EF for ; Thu, 24 Sep 2026 14:58:40 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.128.69 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790261922; cv=none; b=e4MgBerQSr5XIxKF7w77grTddmjSs70KwKps14mySjf3NRHY9xO9lpwhbXSRhP1TzfqRuyAsvGCP8DP6L8O4qiEGi3Gi2X69mMb6ENqfzbAChH0CGNOwl1cC/873ZkLCObd0OuSnqkj+JwTvkLexBeQWtv02R14LS4GszcVaFwU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790261922; c=relaxed/simple; bh=j71Sqg0HqieWplu84cLXf0UWFIJkhiNp/QWh/moIYSM=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=U3Kv3D1IxsI4ojAeJrF9MfwAlDTh6W/uDX2vHxYNYAH7IN8atkeglYjofb8ZNdntycw92Yjznp5DuiOs7f27NVA6ax0bloTMasz67tjOnhPEYfWD4dtDPcpJPpo90TreE0r7kbj6QEbEZraATC1fDft1q8MMmhO4NMD8U5bMmcE= 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=K7nCJLkV; arc=none smtp.client-ip=209.85.128.69 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="K7nCJLkV" Received: by mail-wm1-f69.google.com with SMTP id 5b1f17b1804b1-49e661c6440so12992445e9.3 for ; Thu, 24 Sep 2026 07:58:40 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20251104; t=1790261918; x=1790866718; darn=vger.kernel.org; h=content-type:cc:to:from:subject:message-id:references:mime-version :in-reply-to:date:from:to:cc:subject:date:message-id:reply-to :content-type; bh=p7BbaNLQdlfwNnIQp6SkICmB6RAILmmvxnVT02lEHvo=; b=K7nCJLkVnm+qQI2d2eRHd7M9CROBV97Ua5llehx3Pead34v5HyEE74aoWb9dnhMR2Q bH2AXqVz1Mvxlpz21CgAcaNYsYR/CYq8bkIV7YD+ZXITeNI1wSezRuE9fRM+iWjgI4Sq cI6HffsZT5bFOVKIB6JU709QVnQ7epiQTDHTsqLO6L1gIDS32qNevP99NjIzf/qLWIEZ 2zgxDDkmYKpU9TG6vf/aK/G16UA3B4QXABG5S6i9gmr6j2OH+PZty2MpLfDPMJ7DNCP1 HEKrtjWg8RKjnW//55QqSss57KQDJ8W0bw7zApJtpIP0QKRrkm7K1X9qlUrn+BAkqiiZ t2MQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20260707; t=1790261918; x=1790866718; h=content-type: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:content-type; bh=p7BbaNLQdlfwNnIQp6SkICmB6RAILmmvxnVT02lEHvo=; b=olVXPHIN2FUkIMIFmLV22/hl6WEv6EjHu+/hwf8sZaAcvVuwc2fj3I+uCa7Zt9RwpI Z2Zqpjvn+ykGrnh7mRDTqtND3KCoWdpkiHod5sCqHutKzc3kSfMBlV+9WLjljrc/mk8N 5FsWs9lP2VoOWfzO2yuXFzfF8qZ9QS9PvEfuvY17ab/uyiGle33p3SyPMyBK1B/lIli1 YPVcPq2w1IVr9pyT52PHyeDKrJ6of4R84a1Z7NORhRG2QknJQCwdsXqVEKWvJ/rWAOZz OVYlIV4D3t/nalwNvsi2SnksA0/lkA9+2qVNpDJ8HUG4Un+m7XPaH5xvQWIznSwG33pC ZkQw== X-Forwarded-Encrypted: i=1; AKwUvBzbCnxLgX0NZGRP7uDDXUa2Nsj8ND831u/bySVz88VvFSXfqTX+Wyp5+cJoiyv+ukVTspThdCyb4VuqaUE=@vger.kernel.org X-Gm-Message-State: AFuF++mEOsSXRGcj0LdSs8HonQk1cXBhsLPCjWxh6FPamL7YmKw2nbzO jhZyzZOS6/n4yajoDJFzAcFtAMRc7PNhUcQqCxh+ylyUc73KpAoAH3XSW56DCMYNpS0HXfnb3W3 k9ktZoSpLFRzyizLoVZXreA== X-Received: from wmsr18.prod.google.com ([2002:a05:600c:8b12:b0:49e:602d:8036]) (user=vdonnefort job=prod-delivery.src-stubby-dispatcher) by 2002:a05:600c:8b86:b0:49d:1fd8:b874 with SMTP id 5b1f17b1804b1-49fe66f13c2mr49000245e9.19.1790261917979; Thu, 24 Sep 2026 07:58:37 -0700 (PDT) Date: Thu, 24 Sep 2026 15:57:47 +0100 In-Reply-To: <20260924145754.1285146-1-vdonnefort@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20260924145754.1285146-1-vdonnefort@google.com> X-Mailer: git-send-email 2.56.0.rc1.310.g51773c2048-goog Message-ID: <20260924145754.1285146-14-vdonnefort@google.com> Subject: [PATCH v7 13/20] ring-buffer: Add ring_buffer_read_remote_meta_page() From: Vincent Donnefort To: rostedt@goodmis.org, mhiramat@kernel.org, linux-trace-kernel@vger.kernel.org Cc: mathieu.desnoyers@efficios.com, kernel-team@android.com, linux-kernel@vger.kernel.org, Vincent Donnefort Content-Type: text/plain; charset="UTF-8" In preparation for the introduction of a panic handler for trace remotes, add ring_buffer_read_remote_meta_page(). This is similar to ring_buffer_poll_remote, but it doesn't try to wake up readers and, in the !RING_BUFFER_ALL_CPUS case, uses panic-friendly locks. While at it, update trace_remote_has_cpu() to use this new function instead of ring_buffer_poll_remote(), avoiding unnecessary wakeups when verifying if a CPU buffer is active. Signed-off-by: Vincent Donnefort --- include/linux/ring_buffer.h | 1 + kernel/trace/ring_buffer.c | 41 +++++++++++++++++++++++++++++++++++++ kernel/trace/trace_remote.c | 2 +- 3 files changed, 43 insertions(+), 1 deletion(-) diff --git a/include/linux/ring_buffer.h b/include/linux/ring_buffer.h index eac3e9080c3c..31ad626f48b6 100644 --- a/include/linux/ring_buffer.h +++ b/include/linux/ring_buffer.h @@ -315,6 +315,7 @@ struct ring_buffer_remote { void *priv; }; +int ring_buffer_read_remote_meta_page(struct trace_buffer *buffer, int cpu); int ring_buffer_poll_remote(struct trace_buffer *buffer, int cpu); struct trace_buffer * diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c index f9533a97e2f4..df16e05d7049 100644 --- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c @@ -6902,6 +6902,47 @@ bool ring_buffer_empty_cpu(struct trace_buffer *buffer, int cpu) } EXPORT_SYMBOL_GPL(ring_buffer_empty_cpu); +/** + * ring_buffer_read_remote_meta_page - read the meta page of a remote ring buffer + * @buffer: The ring buffer + * @cpu: The CPU buffer to read (or RING_BUFFER_ALL_CPUS) + * + * Returns: + * 0 on success, or -EINVAL if the CPU is not in the buffer's cpumask. + */ +int ring_buffer_read_remote_meta_page(struct trace_buffer *buffer, int cpu) +{ + struct ring_buffer_per_cpu *cpu_buffer; + + if (cpu != RING_BUFFER_ALL_CPUS) { + unsigned long flags; + bool dolock; + + if (!cpumask_test_cpu(cpu, buffer->cpumask)) + return -EINVAL; + + cpu_buffer = buffer->buffers[cpu]; + + local_irq_save(flags); + dolock = rb_reader_lock(cpu_buffer); + rb_read_remote_meta_page(cpu_buffer); + rb_reader_unlock(cpu_buffer, dolock); + local_irq_restore(flags); + return 0; + } + + guard(cpus_read_lock)(); + + for_each_buffer_cpu(buffer, cpu) { + cpu_buffer = buffer->buffers[cpu]; + + guard(raw_spinlock_irqsave)(&cpu_buffer->reader_lock); + rb_read_remote_meta_page(cpu_buffer); + } + + return 0; +} + int ring_buffer_poll_remote(struct trace_buffer *buffer, int cpu) { struct ring_buffer_per_cpu *cpu_buffer; diff --git a/kernel/trace/trace_remote.c b/kernel/trace/trace_remote.c index 79afb2cdf358..ea0fc347dff8 100644 --- a/kernel/trace/trace_remote.c +++ b/kernel/trace/trace_remote.c @@ -351,7 +351,7 @@ static bool trace_remote_has_cpu(struct trace_remote *remote, int cpu) if (cpu == RING_BUFFER_ALL_CPUS) return true; - return ring_buffer_poll_remote(remote->trace_buffer, cpu) == 0; + return ring_buffer_read_remote_meta_page(remote->trace_buffer, cpu) == 0; } static void __free_ring_buffer_iter(struct trace_remote_iterator *iter, int cpu) -- 2.56.0.rc1.310.g51773c2048-goog