From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from galois.linutronix.de (Galois.linutronix.de [193.142.43.55]) (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 1E33328E61E; Wed, 16 Jul 2025 08:27:15 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=193.142.43.55 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1752654437; cv=none; b=U0YG5SvGQPZrGSzCKHNBC1FnSqQg9Cc5GAqmR17f6CqHX5EcrqgwpMDVAsbkNZ4KY9yuw9f9qz0hEAFmpAGI1aqy67FrlS9TRimweQc16gn5+WBXkhrr8pW7cXA+KfRpB2f8jBmI6XkLVLdr8ACNHYavMy3qaDZyly9zNTPaXlE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1752654437; c=relaxed/simple; bh=4u2lay4hovL5zKYuyCR5r46djizrppNKT21L58JI2mo=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=Cmt7028kdGWhew56WjUatNQ8T+q4+nxcZgg6bb97upL2g7yvQG39DgfJABY1nJpCCt+xL+R/zhFih7uKV4eVmtUg2MwDvqR8kV0xTF5dyTrAPaizCIrrNnnsuPbXy3bo/AUHN7BQ3J2SIK+1k1lcS3r3EtUrAegBwV1fCAljk/o= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linutronix.de; spf=pass smtp.mailfrom=linutronix.de; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=GLJO5q1/; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=mUjFoMAi; arc=none smtp.client-ip=193.142.43.55 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linutronix.de Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linutronix.de Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="GLJO5q1/"; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="mUjFoMAi" Date: Wed, 16 Jul 2025 10:27:12 +0200 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1752654434; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=nNzvlBDk9taOAY9Sh/nOLKJL9wqAlXmEj8E2u0/5lI4=; b=GLJO5q1/uHkLhc/S8mrakS/X5wxx/6DRe0yVrQV/7Ksg5l7tBgWRRGSWZpXR99375ssSbu brGmlrtwan7qczA6OTD7UdmgSyq4QXoP7a4UusK79vc7rHR9t9SRMzmMUhQ0XcpPUGE5u4 sRCdqi0aRfMGROu/2VTEzA6NfTuxQVMPWawFPpV8MB/DfQH8V3wFe4uLL5Fd45rSU8c1jJ oi3falJrB8HGYok9lN6RDe5uwm1jLbnMjaPaTjmmHju4GdAfxrFrsv7gyfpUAMvV2gxvTC +NLZC0kcWa0ziWA4NAgQr6lWr5uruytGgqtkd32guNzosm4Oyi0FaUStxPWJtA== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1752654434; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=nNzvlBDk9taOAY9Sh/nOLKJL9wqAlXmEj8E2u0/5lI4=; b=mUjFoMAi3T5Q6CQaJ2YcYkH/WtpV1LLbFgP5o8EmsqxIiQVDuGkg1VIvehBwORbzo0Wqws VVUYHoFoONQ0pjDQ== From: Nam Cao To: Gabriele Monaco Cc: linux-kernel@vger.kernel.org, Steven Rostedt , linux-trace-kernel@vger.kernel.org, Ingo Molnar , Peter Zijlstra , Tomas Glozar , Juri Lelli , Clark Williams , John Kacur Subject: Re: [PATCH v3 11/17] rv: Retry when da monitor detects race conditions Message-ID: <20250716082712.L9z_ptHK@linutronix.de> References: <20250715071434.22508-1-gmonaco@redhat.com> <20250715071434.22508-12-gmonaco@redhat.com> <20250715152322.Os4lDq_B@linutronix.de> 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-Disposition: inline In-Reply-To: On Wed, Jul 16, 2025 at 10:20:39AM +0200, Gabriele Monaco wrote: > On Tue, 2025-07-15 at 17:23 +0200, Nam Cao wrote: > > If I understand correctly, if after 3 tries and we still fail to > > change the > > state, we will invoke the reactor and trace_error? Doesn't that cause > > a > > false positive? Because it is not a violation of the model, it is > > just a > > race making us fail to change the state. > > > > Yes, that's correct. > My rationale was that, at that point, the monitor is likely no longer > in sync, so silently ignoring the situation is not really an option. > In this case, the reaction includes an invalid current state (because > in fact we don't know what the current state is) and tools may be able > to understand that. Can't you bring the monitor back to the init state, and start over again? I think "da_mon->monitoring = 0;" does the trick? > I know you wouldn't be able to do that in LTL.. By the way, LTL uses > multiple statuses, so this lockless approach may not really work. Let's worry about one thing at a time ;) > I don't see this situation happening often: I only ever observed 2 > events able to race, 4 happening at the same time is wild, but of > course cannot be excluded in principle for any possible monitor. > Yet, I have the feeling a monitor where this can happen is not well > designed and RV should point that out. > Do you have ideas of potential monitors where more than 3 events can > race? > > Perhaps a full blown reaction is a bit aggressive in this situation, as > the /fault/ may not be necessarily in the monitor. > We could think of a special tracepoint or just printing. > > > Same below. > > > > Also, I wouldn't use goto unless necessary. Perhaps it is better to > > put the > > code at "out_react:" and "out_success:" into the loop. But that's > > just my > > personal preference, up to you. > > That could be done if we do a whole different thing when retries run > out, instead of defaulting to out_react. > I liked to avoid excessive indentation with those goto as well but > yeah, it may not be quite necessary. Sure, as I said before, "just my personal preference, up to you." Nam