From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-wr1-f70.google.com (mail-wr1-f70.google.com [209.85.221.70]) (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 0F1FD47DD5A for ; Tue, 21 Jul 2026 10:36:34 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.221.70 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784630196; cv=none; b=LyCHohqxgwVvPgbI/Yy3JObDUiYv9Us/pouGNrCsVAzAzRZkIZB1MNWVynAc0lDa1wpkXa5W9T297uKxq0yDXAKZ17s4VP8YdJcRiAu8dH9VrvYLC7eXL4D7ulbBJhj3bqC8oYsJuvO+4ZFRpe6Wxn8G7TttCohtvE5FbLgw5pw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784630196; c=relaxed/simple; bh=tqb9hClnsbzzrqME6yk9pwSsf3qcS3X3j/sxi4nfxO0=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=mCfN5AWJNFGojtVB/Fjg8jhRSbFIcwi93SVIHUS6dm0Ka+uDfRZ+pJutpTP9ZFbUnIH5pwpTpNFloLgkfJ2ABPmlrh7SvrFf0DYc4jAU+Mn/s18q2xi8OCuOOaTfSfM3F57TiPq9qbu8BkDYSrHHtnGsYqtCXJweP42shUdD/lw= 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=utBsQtw3; arc=none smtp.client-ip=209.85.221.70 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="utBsQtw3" Received: by mail-wr1-f70.google.com with SMTP id ffacd0b85a97d-472c330e555so5438704f8f.1 for ; Tue, 21 Jul 2026 03:36:34 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20251104; t=1784630193; x=1785234993; 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=QaNBgaHJNIj3Shc+crJefx+umJMnjlE9OsiQWnPI6wY=; b=utBsQtw3SIESpQzQpEjmgVtWDQo24WRwAn8vpPmkgNeHPZKZBVNyprnP+IYAPgBWrE XXXwStpJLiFtKwGOa8wOx2OCZQTtPQDPgZkVvaay8L+FGEn/340GKSp9kY0oD8akmpA5 jLDGNhC2Db74x5qkn3qFiaRng1xm7RjzX1jpkZcubaNomSA52MdLEme9ec3C0M8Pz5hy wJqzrGLkxN3Ig5bXNEyUDUpM6Ad5zxkQVzi4bapiLtctOpOsqtYuAPsbCkkICnmIx94S WgkT8wXnjvCzTx18nd8FJEQlGcZFoO+LAUNzERb8IL7ZJhumGIeLEei3C1dtbENrdnJh Nw7A== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1784630193; x=1785234993; 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=QaNBgaHJNIj3Shc+crJefx+umJMnjlE9OsiQWnPI6wY=; b=NDm4/eLjuGBAoWOMks2jqkQ48wfjiSmuynU7ladnIMEL0OKJoyymnxNNYB36Kjb3iK yRPE7bshUuKSug/uvYF3KSMgUp/Ft4yZrtXVVd4PGw1oNIPFnMR9Ct/m9sVstSr89k3L YFP1tfisu7w+etGa7AhsigFG6xbzwCde4jLi7PD2xnSj/cPyAJJtguzj4bl93zUAofSk Zp2pO5GVhq6TKqXt0A834/OjxniyavxKyWL4Nifm+EDa6rA5C5+fq4vNH3/LuoVrWgIl eqhMmOgMoMWceEYHdguPH8VI/Ih/rW0nl4fUQ7+EOTKrrW284RuxzOcF7DEJqiNcIAVn GWUQ== X-Forwarded-Encrypted: i=1; AHgh+RrC3m5yNckCqPvruCAZfUtdmNAIidB5jW/4pgpL60nH30GAwv1Lxbh/QLGLMEhY1svJRG6hY0wvG0+nwLFElLf91gg=@vger.kernel.org X-Gm-Message-State: AOJu0YzatYr1QTD4dtulUzInAixJEsR9T0J+mEA/2+TO5TsxZWcDzUAP +UUb9z/btFBo8MW0/o2k5juZfL7bglXLalGiat640rLR2sUKCIoImyFDch7AKrtIHulj/rc0Tpa e4hjWmpDQadiXBjmnyTrFkg== X-Received: from wrtf11.prod.google.com ([2002:a5d:50cb:0:b0:473:c5ac:de69]) (user=vdonnefort job=prod-delivery.src-stubby-dispatcher) by 2002:a05:6000:4382:b0:47f:8212:54fb with SMTP id ffacd0b85a97d-47f821256cbmr1572826f8f.2.1784630192998; Tue, 21 Jul 2026 03:36:32 -0700 (PDT) Date: Tue, 21 Jul 2026 11:35:56 +0100 In-Reply-To: <20260721103603.342266-1-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: <20260721103603.342266-1-vdonnefort@google.com> X-Mailer: git-send-email 2.55.0.229.g6434b31f56-goog Message-ID: <20260721103603.342266-12-vdonnefort@google.com> Subject: [PATCH v3 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 a ring_buffer_read_remote_meta_page(). This is basically 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 517bdb061083..c35e36c553aa 100644 --- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c @@ -6805,6 +6805,47 @@ 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 c54e1c65d163..fcd2dd754f6e 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) -- 2.55.0.229.g6434b31f56-goog