From: Pavel Machek Subject: Re: [PATCH 3/3] Add timeout feature Date: Wed, 9 Jul 2008 22:48:30 +0200 Message-ID: <20080709204829.GH11006@ucw.cz> References: <20080708232031.GE18195@elf.ucw.cz> <20080709005254.GQ11558@disturbed> <20080709010922.GE9957@mit.edu> <20080709061621.GA5260@infradead.org> <20080708234120.5072111f@infradead.org> <20080708235502.1c52a586@infradead.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: arjan@infradead.org, hch@infradead.org, tytso@mit.edu, t-sato@yk.jp.nec.com, akpm@linux-foundation.org, viro@ZenIV.linux.org.uk, linux-ext4@vger.kernel.org, xfs@oss.sgi.com, dm-devel@redhat.com, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, axboe@kernel.dk, mtk.manpages@googlemail.com To: Miklos Szeredi Return-path: Received: from gprs189-60.eurotel.cz ([160.218.189.60]:1538 "EHLO spitz.ucw.cz" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1755562AbYGIUzz (ORCPT ); Wed, 9 Jul 2008 16:55:55 -0400 Content-Disposition: inline In-Reply-To: Sender: linux-ext4-owner@vger.kernel.org List-ID: On Wed 2008-07-09 09:08:07, Miklos Szeredi wrote: > On Tue, 8 Jul 2008, Arjan van de Ven wrote: > > I tihnk the idea there is > > > > freeze . do the snapshot op . unfreeze . make backup of snapshot > > Ah, so then my proposal would become > > run_frozen mountpoint do-snapshot > do-backup > release-snapshot > > and if they are afraid of deadlocks they can just implement the > timeout in userspace: > > run_frozen -t timeout mountpoint do-snapshot > > 'run_frozen' can be a trivial 30 line app, that can be guaranteed not > to deadlock. Userland apps can be swapped out and need kernel memory allocations during syscalls. I bet even sleep(30) uses kmalloc internally. So yes, even trivial applications can deadlock. -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html