From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from casper.infradead.org (casper.infradead.org [90.155.50.34]) (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 3E8A04156E5; Mon, 3 Aug 2026 14:33:22 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=90.155.50.34 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785767605; cv=none; b=r2BSNw7OkUkWcU4CqDMcFwty9JOianv9UNkwg2ebZf8wGfnqJNdzGh1dLv+cyiqnAEE/MFE+A1BFyi77RRK0FIeo67ZZE/zGsIq99L69IWHEUn6+r3C0MVsBrA0JyZHRpX9j0Fl8KwJ1/IUPy/DAaIlGNTDPXktkbvF0F2ElFwI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785767605; c=relaxed/simple; bh=cdjtm7y8sQ8KvaSXQ6RTib7Bd80T3eEGWbErjDzP5Rc=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=RJKWjr/YKf4+ysXw+LGPNELVFhkLT5IRgxt4yIQcW+fs3EfqxBJUdy53JXQqg+qzT4sBT+e4lKRBU1zljZJDnIdepksoQ8Ow8RoJ+vchTePMQwcUC4LT1GKVEOkL7FO8yzlZrLWrTYJBChdbj8zb2OCmKp14RspjxuZxNfEbzS0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=infradead.org; spf=pass smtp.mailfrom=infradead.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b=X9WCOrk0; arc=none smtp.client-ip=90.155.50.34 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=infradead.org Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=infradead.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="X9WCOrk0" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=SHqeYdMFLe2SuCrvaXaRB/rLWEkPMlLMtR7Ww3H9UK8=; b=X9WCOrk0ZdGuOEOWzqYVkk4JBK He9kYt7HU0Tk/L4Gb4xGH9+sIWu2xwsqTvvLFGRuiri/n5+kgg1TNQ7UjqsB11BZ6sx0kSUEwzgCs mb4g+p++o5mk41/vSeIQ6DWOBK82AXIaITLEG8Dg1mVPal4IQkKK53vUYUGlF1vqzBTjloifTpQdL wMwbUbI7/LPKyKxslLYtxvv00IYz1QLToVmaO7uFPQ1EEPXWjd/L04H3np3Y0bocKQJa/IKLFdxmr Fq0fMRm0GZ2j769mL0DIaNcss/Clqk1qwkd26i5bDmCoV66N/+Gu5hm0PIO9A0lzxl3OqGNwn2BtE saOUX4+w==; Received: from 77-249-17-252.cable.dynamic.v4.ziggo.nl ([77.249.17.252] helo=noisy.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.99.1 #2 (Red Hat Linux)) id 1wqtjA-0000000DmOB-0JJu; Mon, 03 Aug 2026 14:33:16 +0000 Received: by noisy.programming.kicks-ass.net (Postfix, from userid 1000) id 9F49B301127; Mon, 03 Aug 2026 16:33:15 +0200 (CEST) Date: Mon, 3 Aug 2026 16:33:15 +0200 From: Peter Zijlstra To: Boqun Feng Cc: Ingo Molnar , Will Deacon , Waiman Long , Gary Guo , Alice Ryhl , Lyude Paul , Daniel Almeida , Onur =?iso-8859-1?Q?=D6zkan?= , Miguel Ojeda , Danilo Krummrich , linux-kernel@vger.kernel.org, rust-for-linux@vger.kernel.org, Boqun Feng Subject: Re: [PATCH 05/24] irq & spin_lock: Add counted interrupt disabling/enabling Message-ID: <20260803143315.GC788244@noisy.programming.kicks-ass.net> References: <20260731203031.13679-1-boqun@kernel.org> <20260731203031.13679-6-boqun@kernel.org> <20260803102155.GI49951@noisy.programming.kicks-ass.net> <20260803142106.GF687043@noisy.programming.kicks-ass.net> Precedence: bulk X-Mailing-List: linux-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: <20260803142106.GF687043@noisy.programming.kicks-ass.net> On Mon, Aug 03, 2026 at 04:21:06PM +0200, Peter Zijlstra wrote: > No; for one, you cannot elide the preempt_disable/enable() from this > thing. > > It has always been valid to do: > > raw_spin_lock_irq(lock); > ... > raw_spin_unlock(lock); > ... > local_irq_enable(); > > And since raw_spin_unlock() does have the preemption thing, > raw_spin_lock_irq() must too. And the very same argument is still valid > if you now write: > > raw_spin_lock_irq_disable(lock); > ... > raw_spin_unlock(lock); > ... > local_interrupt_enable(); > > Secondly, nothing should 'set' NEED_RESCHED without also immediately > causing a preemption. Notably, scheduler_ipi() is the one that folds TIF_NEED_RESCHED into PREEMPT_NEED_RESCHED for remote reschedules. Other than that, set_preempt_need_resched() must always be used from hardirq context or inside the schedule() loop on current. When used from hardirq context, the interrupt-return path will handle the reschedule, when used inside the schedule() loop, the loop will. No other fiddling of NEED_RESCHED should occur.