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dmarc=pass (p=none dis=none) header.from=goodmis.org Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=goodmis.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=goodmis.org header.i=@goodmis.org header.a=rsa-sha256 header.s=dkim1 header.b=w6oL0KVk Received: from omf20.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay01.hostedemail.com (Postfix) with ESMTP id 6E0721C42C2; Tue, 10 Nov 2026 08:00:29 +0000 (UTC) Received: from [HIDDEN] (Authenticated sender: rostedt@goodmis.org) by omf20.hostedemail.com (Postfix) with ESMTPA id D216720025; Tue, 10 Nov 2026 08:00:26 +0000 (UTC) Date: Tue, 10 Nov 2026 03:00:21 -0500 From: Steven Rostedt To: Breno Leitao Cc: sashiko-bot@kernel.org, Linux trace kernel Subject: Re: [PATCH] ring-buffer: Do not allow reader to see unfinished moved head Message-ID: <20261110030021.57a34e61@fedora> In-Reply-To: References: <20261109032241.55e57d26@fedora> X-Mailer: Claws Mail 4.4.0 (GTK 3.24.52; x86_64-redhat-linux-gnu) X-Mailing-List: linux-trace-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspamout03 X-Rspamd-Queue-Id: D216720025 X-Stat-Signature: fauob9niowjarxcpfu7i3ehenqfpbah5 X-Session-Marker: 726F737465647440676F6F646D69732E6F7267 X-Session-ID: U2FsdGVkX18qy16ZCpb+mBvyyHfcAB6QQBvb87dyG+M= DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=goodmis.org; h=date:from:to:cc:subject:message-id:in-reply-to:references:mime-version:content-type:content-transfer-encoding; s=dkim1; bh=nTu5NUVxbSJd04O7s+0rGqa5jlkhinM8oi1X4DaM1qw=; b=w6oL0KVkGwrZXKGmoj3R4IutkPAooFYt0DmPek4Z5bdsgx0q6oTq7zWEM0M0Q9QeUEYyhszCRzxhjAPZVXdXypwSoAeOSnJIy8WmJ4eEvvzEYV9ylWmgHBjk8oms04waUUmh/Y06S68sp1Mt6mvNA54seyvx3B5Qx4GurYaHmgs= X-HE-Tag: 1794297626-295485 X-HE-Meta: U2FsdGVkX18mIf4ApEiQKIHE6g9LjKdPV19iRvd0lwuO12vhYWAEWt0DI+PRNkcBaeuICPUke1dIO3mwRThaV022ELj1tWwkLrxoIO56bsB7XE5SCPq6O9MtW1UcWfK6FhpazfFDX1S+VUetoSRJoHu6abJEdE5iOAOsz854XJ40VFU/zapxHG1ATz2ObXO3NvYuy7dRRMl06IemtFOPgQaIp28WvASXWurPe+jFY48KDJJwo1gxJU36NUUG05O/OoI7xbJTdDPeV4XlrnGyzj18G3geHXkUs0Hc8pF7Ula6GLGoAf/F4vON12xqLWJe6K4UHdkGYnMW/taFPr63B53OTfi6UDR39Q1KMKQXCxRoCZrIqodNeQ== On Mon, 9 Nov 2026 05:04:50 -0800 Breno Leitao wrote: > Steve, > > Thank for the patch, > > On Mon, Nov 09, 2026 at 08:39:43AM +0000, sashiko-bot@kernel.org wrote: > > > diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c > > > index e760d2fe386fb..cf9e0dc10c88f 100644 > > > --- a/kernel/trace/ring_buffer.c > > > +++ b/kernel/trace/ring_buffer.c > > > @@ -1494,7 +1494,13 @@ rb_set_head_page(struct ring_buffer_per_cpu *cpu_buffer) > > > if (RB_WARN_ON(cpu_buffer, rb_list_head(list->prev->next) != list)) > > > return NULL; > > > > > > - page = head = cpu_buffer->head_page; > > > + /* > > > + * Make sure that the start of the search of the head_page does not > > > + * start between the writer adding the UPDATE and the new HEAD that it > > > + * moves forward. > > > + */ > > > + /* Sync with the writer moving the HEAD in rb_handle_head_page() */ > > > + page = head = smp_load_acquire(&cpu_buffer->head_page); > > > > [Severity: Medium] > > Can the reader's non-atomic update of cpu_buffer->head_page in > > __rb_get_reader_page() race with the writer's new store in > > rb_handle_head_page() and advance cpu_buffer->head_page past the sub-buffer > > marked for update? > > I've asked my robot to test this case, and it was still able to > reproduce the race, even with this patch. Are you still testing with the minimum of 7K? Can you up it to can you echo 11 into buffer_size_kb to see if it is an issue with three sub-buffers? I just want to know if it you are catching issues with something that looks like this: tail v +--HEAD--> subbuf ----> subbuf --+ | | +--------------------------------+ Two subbufs should still be fixed but I want to make sure I'm not looking at two different bugs. -- Steve