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 3E9A73101A7 for ; Tue, 13 Oct 2026 06:46:22 +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=1791873983; cv=none; b=UWZV0pJRdehPNPWlffVe2iNvaNqwWqY5Go0Wo/S6JtAjxk+NYPCgKQ+jBKvhvBqQnOtEkvW5xN2NLhczQt5pT8VNALqQ1YdlY/5p8N2Ibe8x8xvubv2qSvRO79HkBXX8YinwXzvP8/mFmJQIOCZLk2joN8/I80D9ApmjMT9Vu4o= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791873983; c=relaxed/simple; bh=9ovmOPg9Pb4IQ7W/UE15L6p4EfR+xH0ZyiLzY/YGBec=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=bzM/gSFQ9V71M0UHaOF2T9M7ClnQHr/8uLGaKu0yjR/1oIwwj6viwkJOE1hlLhgFtxx8TDRL46t5Qt7x7tUCfuavonFG82k5VpPTBmd7DxFvGH5pSBxKc2UUTCfQZQivRnBhkqcngpxLDmaIfnanhAuJTpXmmsZ2VnQK/esLMfk= 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=FC0BpoXT; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=D75rw7u2; 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="FC0BpoXT"; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="D75rw7u2" Date: Tue, 13 Oct 2026 08:46:17 +0200 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1791873979; 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=utp7+jNU6jDsmQHBvc9ksY2u0WKcyExAM2mAe/mA7sc=; b=FC0BpoXTE/0Y2CA6Y6C96dH2t8n+Zv4YTB0lAyDTJs9YIYTmg3xfmXqyjS75Npw7scEefr 4PAykj3sZAOzQbPQbZtCCNZCzXnMBuQJP5eRdC+OuS74mwk2FD9tXiUQ5q42vxl5238smg PNX1awXA6JjsSy+HPROcjJ1K1IxJ+6NZ0S9BBS1waDb/ZypOgfWH0lIzpvPjCNqZXXeo8Q /kcfucgbEWfqxdbWBVDr938ARLCLhhM1QBi80yCujk/5oZFL65FSIwn0vC4de0jeWuxadb 2m1sBxKaiaNdYM2tstihROBAbv1xVru4wLT6JR7jBfqMkZpQ0CNLyo0hPnh2uA== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1791873979; 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=utp7+jNU6jDsmQHBvc9ksY2u0WKcyExAM2mAe/mA7sc=; b=D75rw7u2BdUCTcXm48SWEe3iqedAdv7tlx3TUAi0/INlR7IByyVqdLAkZ+OoCSb9MoSfXh kInp0ZM9iS9eNOBg== From: Sebastian Andrzej Siewior To: Peter Zijlstra Cc: syzbot , linux-kernel@vger.kernel.org, Thomas Gleixner , Radu Rendec , Ingo Molnar , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Valentin Schneider , K Prateek Nayak Subject: Re: [RFC PATCH v2] sched: irq: cpu-hotplug race vs set_cpus_allowed_ptr() Message-ID: <20261013064617.jw7Sk6un@linutronix.de> References: <20261012103946.aOSAmrRe@linutronix.de> <20261012143047.GV2009045@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=utf-8 Content-Disposition: inline In-Reply-To: <20261012143047.GV2009045@noisy.programming.kicks-ass.net> On 2026-10-12 16:30:47 [+0200], Peter Zijlstra wrote: > > There is nothing that waits for the interrupt thread to complete, > > there is no synchronize_irq() invocation which would be required for > > the deadlock to happen. > > But any other set_cpus_allowed_ptr() call in the kernel can suffer the > same problem, no? Why is the irq thing 'special'? Not saying this is special. > I am struggling to follow along. The actual fail scenario is a > combination of hotplug *and* migrate_disable()? Can we get a picture? let me grab the reproducer and a few tracepoints to make an accurate drawing. > A CPU must not be able to go offline while there are migrate_disable() > tasks on it. Are you saying the migrate_disable() happens after hotplug > already marks the CPU offline? I *think* there were no tasks on it. So based on fading out memory: T on CPU0 in migrate_disable(), assigned to CPU1, schedule(). CPU1 about to go down while the T on CPU0 returns does migrate_enable() and should migrate to CPU1. But this old memory. Let me get the reproducer and get back to you. Sebastian