From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-wm1-f71.google.com (mail-wm1-f71.google.com [209.85.128.71]) (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 6BCDD38944D for ; Wed, 12 Aug 2026 16:13:58 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.128.71 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786551240; cv=none; b=SmwNBfrKyrkNR2mzi3O74QGnvUTTE7VA6YmKsjC9RVD6GnuJnSa3gEbWUVhlm84YyCCwEkznjnpypnze22/qWLCrRHerEoRrymlX0V8nBTziqtMTfhiTpysiK35iA+Wrg9eJ09iK8mck5yDkp5OwsCRit2PwFlq7vGvAwXJy/nc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786551240; c=relaxed/simple; bh=0buim+GLezv7UcmcEYPlcew/FRZnMVn2NaaWHPhgq2k=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=rgVsJwB/qAHkZTcRFB8eEdCIMf1qNq/gWJaPaADcVsaR8W6sAzzcgVjditkJ60mhKcM2dUwsQ2C+08tK1EUKwqv0pqDzDj1oNWUVw+AUzdNMj5hcdb7eu4W5FLtolOyolTc+XQsSJqHF/LX3cH3bsQH68GV94swAg3xRJTVUPKA= 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=juFG/wFG; arc=none smtp.client-ip=209.85.128.71 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="juFG/wFG" Received: by mail-wm1-f71.google.com with SMTP id 5b1f17b1804b1-4997b060af8so7425155e9.1 for ; Wed, 12 Aug 2026 09:13:58 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20251104; t=1786551237; x=1787156037; 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=M/+mM+yAGa1d3mhSt8ncAaOe827emzSuD4j6hilgerk=; b=juFG/wFGWR3l7+juyRoKP5gY/ji/mPMTS8pN8KQ551j/ysbOBUV4Gduve8vuoiDzQt PUZFDbmaydzwb8wMvfkQX4kAcJYzxfoc1DI4u7U57QMNSvTofpSCm4My5P0ndVQW+D/9 KSm7yg6ZUuLgUZ7gclri/RDWdxye9ODmK5n6gtwdoC83ONGAgUU7IlwFGS+TlVHR3NuX F392Zt0G3rdM3LSWIpp+yfjHgrFU2gNi9rl3g9rkl5HHwxLYDuWnRTqX6GMOwzK+sCw1 Ldff5whRcMkcFY421EqV30rjKBB2oXJtdLRUFNyKA4yFthocouDgjJ99Z+FjIHcoedJi s33Q== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1786551237; x=1787156037; 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=M/+mM+yAGa1d3mhSt8ncAaOe827emzSuD4j6hilgerk=; b=BU29M7j/R0OCQpJg1XHGM+X5EvfX9ezxWHLH992C1OabTmyGlrm2hSQAP2jwAbm6Nv MHYnHLSSyEAgAxRbdoHigz0buPsLKVVF4N8vCzXVWis8290+4cY3gNJ49WnCyCp4Pzx0 VIZq63TW8M01oyMszaVxK96MGzLZyYxIBpL380LIt+OEyWXsrtdctnuzREgQOlrP7WmN evgjJp5Q6+aktWjFlFx9RrRMTjeDg83EgU4zMm2SBjkrCsvBVf+Q3HxZYfMXoh4PNKRb VRQMAUiePTrFZjdyeNn999S7GvyWqNv1yDkcx9JelGrCwRH2DnTVri0YsWVVvYvnAJps iYCw== X-Forwarded-Encrypted: i=1; AHgh+RrlrZhMeso+GEs7Tbyro4N4yyqzyDz7AL4FJcSI8HunKDf0QNzqswwyLXCt2PY+3LH3WI7b+oPFENPw/7BHztPSXA4=@vger.kernel.org X-Gm-Message-State: AOJu0YwPSlO4LfuvMRlyYjDvOQGWMwd8KCVOWtHKHyfrM1F4WGJrcVCC EBeCDfb5zR/BcSd2lgB4YSXukoaYLc7UOuypzthEV6sKS3ANHGX+2+ym+MZQU3GZZDwW0tDMLJ7 qTrL3gsEilbU8Q05bSLE1MA== X-Received: from wrsc3.prod.google.com ([2002:adf:fb43:0:b0:47f:8f3e:9a28]) (user=vdonnefort job=prod-delivery.src-stubby-dispatcher) by 2002:a05:600c:468f:b0:499:4892:e84e with SMTP id 5b1f17b1804b1-4997c14569amr67460745e9.11.1786551236585; Wed, 12 Aug 2026 09:13:56 -0700 (PDT) Date: Wed, 12 Aug 2026 17:13:33 +0100 In-Reply-To: <20260812161340.2417322-1-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: <20260812161340.2417322-1-vdonnefort@google.com> X-Mailer: git-send-email 2.55.0.691.gc56d675ccc-goog Message-ID: <20260812161340.2417322-12-vdonnefort@google.com> Subject: [PATCH v5 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 a6f2293f409b..77561f90d0e4 100644 --- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c @@ -6810,6 +6810,47 @@ 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 3a5e0d84c172..9e78267d71f8 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) -- 2.55.0.691.gc56d675ccc-goog