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 B18B146D2C9 for ; Tue, 4 Aug 2026 14:04:06 +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=1785852248; cv=none; b=p3Ix+VquDeSyxM3H/CLh6f6tbsI1kvjAL6mvqIP2DDCYrnjLBb0yEedwaleCGSwEy/UDBkFWNdLzmJEfKixxYNX2SvFVrh7aUYw4HfrVKruGnnzD40Z0qKsgQlP1OUCVEsuUcVP2W3h7PrWaMQ3TeUEKhcTIo02gZZgbu2hQKJw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785852248; c=relaxed/simple; bh=4ykr12J+DjdEXXIEP+A4fCL+3wftmetGDkfrdHensTo=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=RUzkcNpr0ffgkU1PHZLZdeSTHg3aBTDE649J76MkkiFtZg7YoTgGoAjG6HstXzYrJaRenEWLQZZ1JElPqJgYXKeOt1X0yxEKhrDC4Ry7Zsw5EFTZ1zpCEOidZKKO/afr9zO3q9GypumTCwdnrkqkvJTMVuekfQ7nF+wHkdG8Tm4= 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=XEr6iQFy; 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="XEr6iQFy" Received: by mail-wm1-f69.google.com with SMTP id 5b1f17b1804b1-49554715277so30342235e9.1 for ; Tue, 04 Aug 2026 07:04:06 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20251104; t=1785852245; x=1786457045; 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=l1+/wJcPmvAu6E3WJyCfTChbEoVq4yPAHjqItT2NwAs=; b=XEr6iQFyWBjqYSbhUHiebmsGDRJqWLpekEmw0AwR/yyBVC3UVwYkpU60EjuLRAkrAt qwA3M28MFgxXCuAmu4woyvJIuwi44u+udspI1BNnajolSWWCRjKSZvZViQBQVMYdLDnq aZQf3Utc0zSZ5HxRirebQ/sHzJdpTmFektDaY+swCO21fqt/dC+Y/qLLqINXI14+VCvz D7PX7hZPA57tG0Da8l3PDGEyL9amNDwUIhC0YGLQ5Pim0oZwoasFkA6RoyhCnnL6L3wh 4rh2FnybTD+c0QJCyEeEfNwNJaXqTRng5DXlchkG649zjMagJ8fkL8OixE90KdNcn7Ew JocA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1785852245; x=1786457045; 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=l1+/wJcPmvAu6E3WJyCfTChbEoVq4yPAHjqItT2NwAs=; b=K8AjaPNcJQRJVukFBCbA7wTc0Ftoygu4HDS/0i1Xpd1NRSdvEcyrQW5As+8SSiHwYx wGIpLxhyal2BGoteBvc3aUAYl6NcKnmBacvxBIuEr+AhcUwjI2ddunFURbfi2obk8AyQ WZ1TFD8QVpaUpEX6Bv/paPFxB1FqdtmxkzygvrLwvsNJEsf3tGImoM2AC+lJyvWqlIvv Bf398FBW34SKDrnQbAT2mo35qm9vqKNXFis5BGmROgB0TCjytJrB6HYIBZTbPcchYvtk n2N54b0L/kStUvpugKZS2+fUDAialuU/jg4DgxhRWq+B/xpSYDBUru4Pyvi98GwgU7Q9 OyOg== X-Forwarded-Encrypted: i=1; AHgh+RqcuqEytQ85q/J2dK/Fs8sxkKYbhb68/GXog0fRPUNHVOBm2UT1gZ60ABls0EMd+jshSl5kSSOCViF7+9/c4wgMHTY=@vger.kernel.org X-Gm-Message-State: AOJu0YwZYxPiqt2OHS8fLu30XgXBywyyjvqm8ZCTamTQf9zkX0P/wDZo nAfDoYujt7YGNA9/C04+GgxWF1uLrqBcSSjfUJK6p05aQFcBYzFZiotFhKvOLbLRvURStqFN+L0 npKjLJgAemOfhyX0rooIGHg== X-Received: from wmej10.prod.google.com ([2002:a05:600c:42ca:b0:495:66f2:4250]) (user=vdonnefort job=prod-delivery.src-stubby-dispatcher) by 2002:a05:600c:3148:b0:498:11b5:3ff7 with SMTP id 5b1f17b1804b1-49811b54490mr251707165e9.18.1785852244620; Tue, 04 Aug 2026 07:04:04 -0700 (PDT) Date: Tue, 4 Aug 2026 15:03:26 +0100 In-Reply-To: <20260804140333.797210-1-vdonnefort@google.com> Precedence: bulk X-Mailing-List: linux-trace-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20260804140333.797210-1-vdonnefort@google.com> X-Mailer: git-send-email 2.55.0.571.g244d577d93-goog Message-ID: <20260804140333.797210-12-vdonnefort@google.com> Subject: [PATCH v4 11/18] 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 diff --git a/include/linux/ring_buffer.h b/include/linux/ring_buffer.h index 0670742b2d60..3c0de6593c81 100644 --- a/include/linux/ring_buffer.h +++ b/include/linux/ring_buffer.h @@ -299,6 +299,7 @@ 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 239041704e4d..4bb1a7780860 100644 --- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c @@ -6807,6 +6807,47 @@ 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 58a38f3d4902..2421550d5601 100644 --- a/kernel/trace/trace_remote.c +++ b/kernel/trace/trace_remote.c @@ -350,7 +350,7 @@ 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) -- 2.55.0.571.g244d577d93-goog