From mboxrd@z Thu Jan 1 00:00:00 1970 From: Al Viro Subject: Re: [PATCH block/for-4.5-fixes] writeback: keep superblock pinned during cgroup writeback association switches Date: Fri, 19 Feb 2016 20:18:06 +0000 Message-ID: <20160219201805.GZ17997@ZenIV.linux.org.uk> References: <20160215210047.GN3965@htj.duckdns.org> <20160216182457.GO3741@mtj.duckdns.org> <20160217205721.GE14140@quack.suse.cz> <20160217210744.GA6479@mtj.duckdns.org> <20160217223009.GN14140@quack.suse.cz> <20160217230231.GC6479@mtj.duckdns.org> <20160218095538.GA4338@quack.suse.cz> <20160218130033.GE6479@mtj.duckdns.org> Mime-Version: 1.0 Return-path: Content-Disposition: inline In-Reply-To: <20160218130033.GE6479@mtj.duckdns.org> Sender: linux-kernel-owner@vger.kernel.org List-ID: Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Tejun Heo Cc: Jan Kara , Tahsin Erdogan , Jens Axboe , cgroups@vger.kernel.org, Theodore Ts'o , Nauman Rafique , linux-kernel@vger.kernel.org, Jan Kara On Thu, Feb 18, 2016 at 08:00:33AM -0500, Tejun Heo wrote: > So, the question is why aren't we just using s_active and draining it > on umount of the last mountpoint. Because, right now, the behavior is > weird in that we allow umounts to proceed but then let the superblock > hang onto the block device till s_active is drained. This really > should be synchronous. This really should not. First of all, umount -l (or exit of the last namespace user, for that matter) can leave you with actual fs shutdown postponed until some opened files get closed. Nothing synchronous about that. If you need details on s_active/s_umount/etc., I can give you a braindump, but I suspect your real question is a lot more specific. Details, please...