From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Sun, 22 Jun 2003 23:32:35 -0700 From: Andrew Morton Subject: Re: [PATCH] Fix vmtruncate race and distributed filesystem race Message-Id: <20030622233235.0924364d.akpm@digeo.com> In-Reply-To: <20030623032842.GA1167@us.ibm.com> References: <133430000.1055448961@baldur.austin.ibm.com> <20030612134946.450e0f77.akpm@digeo.com> <20030612140014.32b7244d.akpm@digeo.com> <150040000.1055452098@baldur.austin.ibm.com> <20030612144418.49f75066.akpm@digeo.com> <184910000.1055458610@baldur.austin.ibm.com> <20030620001743.GI18317@dualathlon.random> <20030623032842.GA1167@us.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: paulmck@us.ibm.com Cc: andrea@suse.de, dmccr@us.ibm.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org List-ID: "Paul E. McKenney" wrote: > > > but you can't trap this with a single counter increment in do_truncate: > > > > CPU 0 CPU 1 > > ---------- ----------- > > do_no_page > > truncate i_size = new_i_size; > > increment counter > > read counter > > ->nopage check i_size > > vmtruncate > > read counter again -> different so retry > > > > thanks to the second counter increment after vmtruncate in my fix, the > > above race couldn't happen. > > The trick is that CPU 0 is expected to have updated the filesystem's > idea of what pages are available before calling vmtruncate, > invalidate_mmap_range() or whichever. i_size has been updated, and filemap_nopage() will return NULL. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: aart@kvack.org