From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 AF92931E831; Wed, 3 Jun 2026 19:13:36 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780514017; cv=none; b=CC10GAfKh3x2KVptQIIPb42Uoj7Z0My+Gpe5Kpw/0q9wYLp01JPUG0ut7FCnqzgwPHrZqMIWPAa/4tR6T1UsEZVQdBC0EJWWjzGN1Im+XXF8aUUFWxuBHwP+Pm7tsNtnVFiwdeH/x4B0prSqyl2QIjIDmoUntONWAOURLSnwHu4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780514017; c=relaxed/simple; bh=7jCRXDPkmj9G/HVahwPw/Vzo6xW8XGTpuLLGduy5aYI=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=EkjJzqnFD16Hxs+tlWPkjdODHj/NMlKbCCWUHGz/rzjmxRC15HDPztkeeBn9tKLNkC8pexBU1DvSyBAVgGubmFL8HQv8UHFBjZIp3EWoi4jqGc0uy6STmutggE9G7wyUpfSVhomxszXLd+MwkLbAM+rphFxkk+Ia7pjN3gBPH+s= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=D/r/IFo6; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="D/r/IFo6" Received: by smtp.kernel.org (Postfix) with ESMTPSA id ED0951F00893; Wed, 3 Jun 2026 19:13:32 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1780514016; bh=JRRc8ydgJvk3dCRJzMoxz+ZM/cka9KnQs2wvZBmcrYw=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=D/r/IFo676vUApletMFZxTexyQsKoBkTA1G9DhNDmguCEgLDxVNm1u/AYN4XmV8Wl lJQcodJTA0k7HSI+dsqUOU7oyJEFY0g3/PE1QCVBkPdo1akBrAhfJF523TyurX9LZD PbUweaF1Epcv1Ys2i6q9cmWQ8zInCEffbwOSivMSBbc8ggeM26RJ3PXqhsAeh43GsF Mak2qHILhAzFXX221XyWE/VgebrN8XxVeHYGRXtqXasP3Lp7nBTjDqNx344DCG85QW T9a1Tr5UFhj6wue31HJp2HEimqryurvP/0EfhwpE+1HcQHw2MGF5Tagw/WlpTejf0c lNksNWWghOJ+Q== Message-ID: Date: Wed, 3 Jun 2026 21:13:30 +0200 Precedence: bulk X-Mailing-List: linux-trace-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: mm/memory-failure tracepoint change breaks userspace rasdaemon To: Steven Rostedt Cc: Borislav Petkov , "Zhuo, Qiuxu" , "mchehab+huawei@kernel.org" , "Luck, Tony" , "akpm@linux-foundation.org" , "linmiaohe@huawei.com" , "xieyuanbin1@huawei.com" , "Lai, Yi1" , "linux-kernel@vger.kernel.org" , "linux-edac@vger.kernel.org" , "linux-mm@kvack.org" , "linux-trace-kernel@vger.kernel.org" , Linus Torvalds References: <20260603121707.7eccb9fb@gandalf.local.home> <20260603161947.GBaiBUI7C8WWPwD84S@fat_crate.local> <0c16bf3d-7c6d-4e28-b200-03b7d0ef714a@kernel.org> <20260603130006.7d2c4a62@gandalf.local.home> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 6/3/26 19:00, Steven Rostedt wrote: > On Wed, 3 Jun 2026 18:26:24 +0200 > "David Hildenbrand (Arm)" wrote: > >> Yeah, I was fearing that when I read in [2]: >> >> "It has become clear in the past that this promise extends to >> tracepoints, most notably in 2011 when a tracepoint change broke >> powertop and had to be reverted." > > Technically the issue is with trace events and not tracepoints. The > difference is that a trace event is created via the TRACE_EVENT() macro > which defines what is to be collected from the tracepoint and exposes that > information to tracefs which applications can easily see. > > A tracepoint is simply the hook in the code that you can attach to. Trace > events create a callback from that hook to extract the data from the > tracepoint to fill in the fields. > >> >> Which means that I now also fully understand >> >> "Some kernel maintainers prohibit or severely restrict the addition of >> tracepoints to their subsystems out of fear that a similar thing could >> happen to them. " >> >> Whatever the result of this discussion will be, I'll try to document it. > > You can still create a tracepoint without creating a trace event by using > the DECLARE_TRACE() macro. The scheduler subsystem uses that quite > extensively. That creates a tracepoint without exposing it to tracefs. The > runtime verifier uses these hooks to monitor the scheduler. > > But you can still connect to these tracepoints from tracefs via a tprobe. A > tprobe hooks to tracepoints that you need the source code to find (just > like a fprobe hooks to any function). Thus applications *can't* rely on > them because there's nothing there to tell you it exists or not. Thanks, that makes sense! So, would it be fair to say that, in general, what's exposed through /sys/kernel/tracing/events/ is stable ABI? Would the following be sufficient to avoid a full revert and the dependency on CONFIG_RAS? diff --git a/include/trace/events/memory-failure.h b/include/trace/events/memory-failure.h index aa57cc8f896b..c46b17602578 100644 --- a/include/trace/events/memory-failure.h +++ b/include/trace/events/memory-failure.h @@ -1,6 +1,7 @@ /* SPDX-License-Identifier: GPL-2.0 */ #undef TRACE_SYSTEM -#define TRACE_SYSTEM memory_failure +/* Some user space relies on ras/memory_failure_event */ +#define TRACE_SYSTEM ras #define TRACE_INCLUDE_FILE memory-failure #if !defined(_TRACE_MEMORY_FAILURE_H) || defined(TRACE_HEADER_MULTI_READ) -- Cheers, David