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 B76B2195FE8; Wed, 28 May 2025 06:12:59 +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=1748412781; cv=none; b=NGyM4KnOb/AS9hxBGkUBW7RRrx9znlRR0/kw3oKMh8gqA4OzoirNaN76Qz9DK7XfXhHo2GL347gIaDN5oYP2Yq7kVWBeSIhoy0oaoi9WYJZ3oFDcL+aCBw47nHPhJhJ66eXb8uKQq72Uzx+XQ07Wmz305dP2v4MHKwjU7lpI2J4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1748412781; c=relaxed/simple; bh=rxFzwGyf3zCL39xFxcp2SmNxp4T6cx0JLgHayOZN5NA=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=U2HuWpzLxaVP2YG8C9us8rRpV7ON/NdrPiv7MNbPDdBsebgynINrsnvopSJH2yigwBHOLGE/+BYuUYN9aE97r3ymj9cXWIuhy9N3QpSoPPAaT5CHltfkyMJ1QbVEpn97ZTGo4oQ/XT3kgAVh/RN9rzgJ7SaN5SFooGNMf7+E1Vo= 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=YB5LvelA; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=FW7/wTKj; 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="YB5LvelA"; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="FW7/wTKj" Date: Wed, 28 May 2025 08:12:52 +0200 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1748412778; 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: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=rxFzwGyf3zCL39xFxcp2SmNxp4T6cx0JLgHayOZN5NA=; b=YB5LvelAj30FQYO2KPZ4V8lgBUjptsHgU1eM41hOEsnaNCxUdxYRoRsHKgc5QoSpDEACra EVknvQu66nPBbmoxFJ9OljtKPLT3optsVo3xXiTqGYB7O2+24zAx2xt/ghWWpoq3QH36Lt oQRDbcCoW67/wEnMnEaaWBGGr6cnI77zIcj9/zV5bqe8leI3YkigugCdu7+XbO0ibX1qBo 0TMQekejoSMClnp5oIWpSD7L3zJi59ZyBOBRiWJ/48MqkMpSkZaDdr1ySGYH6l18ntGg1A rbnKupKVQ/fPfj23slPAakEeQkfmBgvsml0eaCnz0K6gpTsqsQqLV4nTIjjjrQ== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1748412778; 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: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=rxFzwGyf3zCL39xFxcp2SmNxp4T6cx0JLgHayOZN5NA=; b=FW7/wTKjR3KqSk2JP+WuWGgnn8tW5v3fMTN/0/O30mcxDaZMovykk3NmSDpnLOhLTt0v2d CZI9QzscaJE865CA== From: Nam Cao To: Holger =?iso-8859-1?Q?Hoffst=E4tte?= Cc: Alexander Viro , Christian Brauner , Jan Kara , Sebastian Andrzej Siewior , John Ogness , Clark Williams , Steven Rostedt , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-rt-devel@lists.linux.dev, linux-rt-users@vger.kernel.org, Joe Damato , Martin Karsten , Jens Axboe , Frederic Weisbecker , Valentin Schneider Subject: Re: [PATCH v2] eventpoll: Fix priority inversion problem Message-ID: <20250528061252.AeDA23yH@linutronix.de> References: <20250523061104.3490066-1-namcao@linutronix.de> <3475f3f1-4109-b6ac-6ea6-dadcdec8db1f@applied-asynchrony.com> Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <3475f3f1-4109-b6ac-6ea6-dadcdec8db1f@applied-asynchrony.com> On Wed, May 28, 2025 at 07:57:26AM +0200, Holger Hoffstätte wrote: > I have been running with v2 on 6.15.0 without any issues so far, but just > found this in my server's kern.log: Thanks for testing! > It seems the condition (!n) in __ep_remove is not always true and the WARN_ON triggers. > This is the first and only time I've seen this. Currently rebuilding with v3. Yeah this means __ep_remove() thinks the item is in epoll's rdllist and attempt to remove it, but then couldn't actually find the item in the list. __ep_remove() relies on the 'ready' flag, and this flags is quite complicated. And as my colleague pointed out off-list, I got memory ordering wrong for this flag. Therefore it is likely that you stepped on a bug with this flag. I got rid of this flag in v3, so hopefully the problem goes away. Best regards, Nam