Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752749AbaJYTvV (ORCPT ); Sat, 25 Oct 2014 15:51:21 -0400 Received: from zeniv.linux.org.uk ([195.92.253.2]:41442 "EHLO ZenIV.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751816AbaJYTvT (ORCPT ); Sat, 25 Oct 2014 15:51:19 -0400 Date: Sat, 25 Oct 2014 18:06:09 +0100 From: Al Viro To: Miklos Szeredi Cc: Linus Torvalds , Linux-Fsdevel , Kernel Mailing List , linux-unionfs@vger.kernel.org Subject: Re: [GIT PULL] overlay filesystem v25 Message-ID: <20141025170609.GK7996@ZenIV.linux.org.uk> References: <20141023232539.GA4662@tucsk.piliscsaba.szeredi.hu> <20141024022055.GH7996@ZenIV.linux.org.uk> <20141024032422.GI7996@ZenIV.linux.org.uk> <20141025081845.GJ7996@ZenIV.linux.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, Oct 25, 2014 at 11:53:52AM +0200, Miklos Szeredi wrote: > Yes, but it's not about race with copy-up (which the ovl_path_upper() > protects against), but race of two fsync calls with each other. If > there's no synchronization between them, then that od->upperfile does > indeed count as lockless access, no matter that the assignment was > done under lock. p = global; if (!p) { // outside of lock p = alloc(); grab lock if (!global) { global = p; } else { destroy(p); p = global; } drop lock } is a very common pattern, especially if you look for cases when lock is a spinlock and allocation is blocking (in those cases you'll often see destroy() part done after dropping the lock; that's where what I fucked up in what I'd originally pushed. And it wasn't even needed - fput() under ->i_mutex is OK...) -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/