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 C132F24339D; Thu, 17 Apr 2025 15:31:29 +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=1744903891; cv=none; b=L7dnOpph1uJ3I7+wvZpkxqbV5U4rqqejpFj/45VuOnFaC9B9GoJLwKo8kEJUWsfHhOVWPGIamry27DiZMJjt2mOmOT7UNL6nvN0vRGr0lusH3mqK8hZjBiilvA/BlCnJ7c0MQe/6VWWO7vLxhJYL8q3jLsRAn3KvegT1mSLAYIA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1744903891; c=relaxed/simple; bh=wH4xbnF0tJ+lpv6tI2RocL517peQVILv0bdOqBny/aM=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=t4BHXW1yceZsdboNkkQpgWO05bSt1DMQBwUh/wf7J7hNGbRQRddtvaoYrU12aGXGJkw/l3US5c6anBzgy+etDQfrVpPNvY/b3ZXiYHv4oxhPj/ZKPXq6ERBIahZ+FgaCVOVsDM2GQviR2iQ2batmFuF8LlZnmBMlDpzkzNXjmT4= 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=r7fnejSH; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=RhJ9nZiM; 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="r7fnejSH"; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="RhJ9nZiM" Date: Thu, 17 Apr 2025 17:31:26 +0200 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1744903888; 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=jPz1GvAsRDSeWCTqbiCwXpDsU6owFfdI+6h+yJOwEN8=; b=r7fnejSHrmuXZG3gkKO6oax4/vQkB0tYQslhdQS4NLgWa1Qg7ycLsssCP3Achi+GJeFvY8 mAD+Vw4zPOSbHJvK8L5trOLqdaiASJhiAjpLesCPTAwbA/wjDeSr4waGGTXgmVaDB5jsXp jRxWplPFXqCFcWlwldZDA7wsDXWrEyNROGH0xgQJfdZj0vjQ+RYBgpLJpAbQVfJvYsg7lm zUuZxst0QJmcuxO3F91W3/Mh6cubMsrvp5XUOv6sWuSefQt0ECKxHGLzJD5V6wCR5aUpjF 3MhWFRX+Zx4PIIBnsG1BG1iYhCKP4txp1uahOX39RtEzxo9S3ZlzAP+ehhXthg== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1744903888; 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=jPz1GvAsRDSeWCTqbiCwXpDsU6owFfdI+6h+yJOwEN8=; b=RhJ9nZiMb5QGNDaj87nqAmzhO5W3mAIsyA/Z0DzqINI7yVN+20Qn/BOe6+bj3GyNENvfiJ YrSPRn/ltCnQImBg== From: Sebastian Andrzej Siewior To: Christian Brauner Cc: Ian Kent , Mark Brown , Eric Chanudet , Alexander Viro , Jan Kara , Clark Williams , Steven Rostedt , Ian Kent , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-rt-devel@lists.linux.dev, Alexander Larsson , Lucas Karpinski , Aishwarya.TCV@arm.com Subject: Re: [PATCH v4] fs/namespace: defer RCU sync for MNT_DETACH umount Message-ID: <20250417153126.QrVXSjt-@linutronix.de> References: <20250408210350.749901-12-echanude@redhat.com> <20250417-wolfsrudel-zubewegt-10514f07d837@brauner> <20250417-abartig-abfuhr-40e558b85f97@brauner> <20250417-outen-dreihundert-7a772f78f685@brauner> <20250417-zappeln-angesagt-f172a71839d3@brauner> 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: <20250417-zappeln-angesagt-f172a71839d3@brauner> On 2025-04-17 17:28:20 [+0200], Christian Brauner wrote: > > So if there's some userspace process with a broken NFS server and it > > does umount(MNT_DETACH) it will end up hanging every other > > umount(MNT_DETACH) on the system because the dealyed_mntput_work > > workqueue (to my understanding) cannot make progress. > > Ok, "to my understanding" has been updated after going back and reading > the delayed work code. Luckily it's not as bad as I thought it is > because it's queued on system_wq which is multi-threaded so it's at > least not causing everyone with MNT_DETACH to get stuck. I'm still > skeptical how safe this all is. I would (again) throw system_unbound_wq into the game because the former will remain on the CPU on which has been enqueued (if speaking about multi threading). Sebastian