From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 66CC425771; Thu, 26 Feb 2026 12:56:59 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772110619; cv=none; b=G3CHUQnaGNSo5bMOYi/jggY9+ZNh+DBzxIwqWP3nUYa5MDIa25ZNSyLZ5/J6REqje33UyT5AWn2l2PUAO2yQGR/BkDbW1owYOpq+5jaCW5/ngDwKaJREWmiid1TY2ATpnCbV1QgpQk3GqinBgMH3+hkdE3QT20oIX+rgj+Yk/bQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772110619; c=relaxed/simple; bh=28vwV37Zzv8vY7Xj+jR5X+7eWEaI0M112mDdqvWwpq0=; h=Date:From:To:Cc:Subject:Message-Id:In-Reply-To:References: Mime-Version:Content-Type; b=qAIQUHoLSLU2ZEvSUeGJYH26AJl2jfYwu21k/2HGVHC9jyoWWzGZor8GXI05IhGuwlU/stRA/hpjh/c8Et5CDXNEZNum1UEh/nFl1GVMwiSaGqyWuaheaPeRambsmu3lEHWjkEQvEyoUD+oOOGHGSyYAbcJTaorXR5c3cb3oihg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=iCqywI9D; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="iCqywI9D" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 229F7C116C6; Thu, 26 Feb 2026 12:56:58 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1772110619; bh=28vwV37Zzv8vY7Xj+jR5X+7eWEaI0M112mDdqvWwpq0=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=iCqywI9DkT3ja/mduMQD+XKeNenZG3Nq83S2ehimIwd0Qnxm42U7u0olgmx27BPJL LjGVoQ/YRG2sA5rMDjKlm02qbqwpQhHrIbsu/USfSgxf5ij741iGxAE0XePdSDMk6X ugGh4FEdt9OGwOmhsQxutQoE5JuWYiSDENcXY5fKTNPlDT39ydifz9Oj26u6XNiC7C JCzrTHmKmlvpvQKs6QHbUBU6g9UEG3CQlPa6AcyDq7S0d7za9CRzrvtfEHsG9uGw6/ d7gES5WVsa0eHQVFwR/zai2Cx1ktW1KpTelydW72vBzEmBF6t30BnHuoLPcm7SRPMF 0ozFlUCbBzjIQ== Date: Thu, 26 Feb 2026 21:56:56 +0900 From: Masami Hiramatsu (Google) To: "Masami Hiramatsu (Google)" Cc: Steven Rostedt , Mathieu Desnoyers , linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org Subject: Re: [PATCH v4 1/3] ring-buffer: Flush and stop persistent ring buffer on panic Message-Id: <20260226215656.7f4d5368393c417fd8da5a2f@kernel.org> In-Reply-To: <177191596224.435720.8250761603256925623.stgit@mhiramat.tok.corp.google.com> References: <177191595057.435720.10116014529518464418.stgit@mhiramat.tok.corp.google.com> <177191596224.435720.8250761603256925623.stgit@mhiramat.tok.corp.google.com> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Precedence: bulk X-Mailing-List: linux-trace-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Tue, 24 Feb 2026 15:52:42 +0900 "Masami Hiramatsu (Google)" wrote: > From: Masami Hiramatsu (Google) > > On real hardware, panic and machine reboot may not flush hardware cache > to memory. This means the persistent ring buffer, which relies on a > coherent state of memory, may not have its events written to the buffer > and they may be lost. Moreover, there may be inconsistency with the > counters which are used for validation of the integrity of the > persistent ring buffer which may cause all data to be discarded. > > To avoid this issue, stop recording of the ring buffer on panic and > flush the cache of the ring buffer's memory. > > Fixes: e645535a954a ("tracing: Add option to use memmapped memory for trace boot instance") > Cc: stable@vger.kernel.org > Signed-off-by: Masami Hiramatsu (Google) > --- > Changes in v3: > - update patch description. > --- > kernel/trace/ring_buffer.c | 21 +++++++++++++++++++++ > 1 file changed, 21 insertions(+) > > diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c > index f16f053ef77d..3eb124c93d72 100644 > --- a/kernel/trace/ring_buffer.c > +++ b/kernel/trace/ring_buffer.c > @@ -6,6 +6,7 @@ > */ > #include > #include > +#include > #include > #include > #include > @@ -589,6 +590,7 @@ struct trace_buffer { > > unsigned long range_addr_start; > unsigned long range_addr_end; > + struct notifier_block flush_nb; > > struct ring_buffer_meta *meta; > > @@ -2471,6 +2473,16 @@ static void rb_free_cpu_buffer(struct ring_buffer_per_cpu *cpu_buffer) > kfree(cpu_buffer); > } > > +static int rb_flush_buffer_cb(struct notifier_block *nb, unsigned long event, void *data) > +{ > + struct trace_buffer *buffer = container_of(nb, struct trace_buffer, flush_nb); > + > + ring_buffer_record_disable(buffer); I found this was a wrong API. I have to use ring_buffer_record_off(). > + flush_kernel_vmap_range((void *)buffer->range_addr_start, > + buffer->range_addr_end - buffer->range_addr_start); This does nothing on arm64. Thanks, > + return NOTIFY_DONE; > +} > + > static struct trace_buffer *alloc_buffer(unsigned long size, unsigned flags, > int order, unsigned long start, > unsigned long end, > @@ -2590,6 +2602,12 @@ static struct trace_buffer *alloc_buffer(unsigned long size, unsigned flags, > > mutex_init(&buffer->mutex); > > + /* Persistent ring buffer needs to flush cache before reboot. */ > + if (start & end) { > + buffer->flush_nb.notifier_call = rb_flush_buffer_cb; > + atomic_notifier_chain_register(&panic_notifier_list, &buffer->flush_nb); > + } > + > return_ptr(buffer); > > fail_free_buffers: > @@ -2677,6 +2695,9 @@ ring_buffer_free(struct trace_buffer *buffer) > { > int cpu; > > + if (buffer->range_addr_start && buffer->range_addr_end) > + atomic_notifier_chain_unregister(&panic_notifier_list, &buffer->flush_nb); > + > cpuhp_state_remove_instance(CPUHP_TRACE_RB_PREPARE, &buffer->node); > > irq_work_sync(&buffer->irq_work.work); > -- Masami Hiramatsu (Google)