From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from relay.hostedemail.com (smtprelay0011.hostedemail.com [216.40.44.11]) (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 A8845318EC0; Wed, 7 Jan 2026 16:16:49 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=216.40.44.11 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1767802618; cv=none; b=lVvw+Ah+diELJnFrj8ZJgRX7KjxU2yRM9emmjmE3MlbWZPP+oOaX/4ETjoGMlqD804NDAWjuiNP1ncCYbVhvU3c9+oLKEHEL8dwy6YzoRCDNd0f4OZWH0acc7FZ7ZHzi4e2xIgGvZubXc+mf43S/XnNQFj1P/pVWHGIlbqhzem0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1767802618; c=relaxed/simple; bh=ZPXqCY0tho6GkwmA6fbStYsMzfpN/ihT2eAucHg9+6g=; h=Date:From:To:Cc:Subject:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=mKiR2PelAHhvySSwi0BP5Zhf+soeB3j2ZAT6qedtYvcb55Qj9QTmfChgW4JdJmQXSQgL064fLMtrJfoClaWVwB7//tkd/mlV2Mqi6MkE8UWec/0XYn/wLPnb57BE6dQszLvFowlqMWzIOOS15QRGgQ109bjgYaesAlHpc5ESB64= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=goodmis.org; spf=pass smtp.mailfrom=goodmis.org; arc=none smtp.client-ip=216.40.44.11 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=goodmis.org Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=goodmis.org Received: from omf17.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay04.hostedemail.com (Postfix) with ESMTP id C35701A0434; Wed, 7 Jan 2026 16:16:44 +0000 (UTC) Received: from [HIDDEN] (Authenticated sender: rostedt@goodmis.org) by omf17.hostedemail.com (Postfix) with ESMTPA id ADB0218; Wed, 7 Jan 2026 16:16:42 +0000 (UTC) Date: Wed, 7 Jan 2026 11:17:09 -0500 From: Steven Rostedt To: Petr Tesarik Cc: Masami Hiramatsu , Mathieu Desnoyers , Sebastian Andrzej Siewior , Clark Williams , linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, linux-rt-devel@lists.linux.dev Subject: Re: [PATCH] ring-buffer: Use a housekeeping CPU to wake up waiters Message-ID: <20260107111709.0d115cd8@gandalf.local.home> In-Reply-To: <20260107105137.4cf9a67e@mordecai> References: <20260106091039.2012108-1-ptesarik@suse.com> <20260106170405.425f469e@gandalf.local.home> <20260107085009.58fcffd4@mordecai> <20260107105137.4cf9a67e@mordecai> X-Mailer: Claws Mail 3.20.0git84 (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 X-Stat-Signature: inzb3rjx98gangpw8ut1k8r1t7gaxxdb X-Rspamd-Server: rspamout01 X-Rspamd-Queue-Id: ADB0218 X-Session-Marker: 726F737465647440676F6F646D69732E6F7267 X-Session-ID: U2FsdGVkX19wzP8VKZmWVZCPfE0i6TVAtAqY+P8NKJk= X-HE-Tag: 1767802602-156917 X-HE-Meta: U2FsdGVkX19Kri1jK5kubktxQQFJRrmq4ZI847AS2na2jPx5t5RfZXCXYwig/ta7ww642uasvv6l69u0UB28AT1SyNeL0O4RYptw0XHlE3c1llKWYlKarx3fTGG1umQlyn7kX30f+QPsOCqQe1n0mhkiV+mwVJ3QgLDBckoQwDjYgpdjsLnfhouY26iS1WZgk/4jAfpZ//LWfqTrqRho6yx3/480jWCSYRPqwfWzv75qfW5+hvD4A0Y7iEIikq1SC42w0CxS9k9EHhv+D1PEBv9RfB1n2fn7UYprmMCeYl1uOsrC1s8L3P5qQoqIcrpZihHfvTholYVDZ/zXoVlRoZKdhVJDMshlerQfhZ3BEHP7IVGcMVYuK35VP1dJ9a4s On Wed, 7 Jan 2026 10:51:37 +0100 Petr Tesarik wrote: > Erm. It's actually good I had a look. :-( > > A helpful comment in irq_work_queue_on() explains that "arch remote IPI > send/receive backend aren't NMI safe". That's something I wasn't aware > of, and I'm afraid it's the end of story. The comment is followed by a > WARN_ON_ONCE(in_nmi()), and I can easily trigger it with "perf top" > while nmi:nmi_handler is traced. > > Please, remove the patch again. I'm sorry. Or we simply change it to: static inline void rb_irq_work_queue(struct rb_irq_work *irq_work) { int cpu; /* irq_work_queue_on() is not allowed in NMI context */ if (in_nmi()) { irq_work_queue(&irq_work->work, cpu); return; } cpu = housekeeping_any_cpu(HK_TYPE_KERNEL_NOISE); /* * If CPU isolation is not active, cpu is always the current * CPU, and the following is equivallent to irq_work_queue(). */ irq_work_queue_on(&irq_work->work, cpu); } -- Steve