From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Tue, 21 Nov 2006 13:14:10 -0600 From: Matt Mackall Subject: Re: build error: sparsemem + SLOB Message-ID: <20061121191410.GL4797@waste.org> References: <20061120183632.GD4797@waste.org> <20061121143253.51B5.Y-GOTO@jp.fujitsu.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20061121143253.51B5.Y-GOTO@jp.fujitsu.com> Sender: owner-linux-mm@kvack.org Return-Path: To: Yasunori Goto Cc: Hugh Dickins , Christoph Lameter , Randy Dunlap , linux-mm@kvack.org, Pekka Enberg List-ID: On Tue, Nov 21, 2006 at 02:57:23PM +0900, Yasunori Goto wrote: > > On Mon, Nov 20, 2006 at 05:28:24PM +0000, Hugh Dickins wrote: > > > On Mon, 20 Nov 2006, Christoph Lameter wrote: > > > > > > > > As far as I can tell SLOB is fundamentally racy since it does not support > > > > SLAB_DESTROY_BY_RCU correctly. F.e. The constructor for the anon_vma will > > > > be called on alloc without regard for RCU, we free an item and reuse it > > > > without regard to RCU. This can potentially mess up the anon_vma locking > > > > state while we access it. > > > > > > Good find! > > > > > > > Is SLOB used at all or have we been lucky so far? > > > > > > Lucky so far. Well, we'd actually have to be quite unlucky to ever > > > see what page_lock_anon_vma/SLAB_DESTROY_BY_RCU are guarding against. > > > > > > But you're absolutely right that users should not be exposed to such > > > unsafety. I'd say SLOB should be disallowed if SMP. > > > > SLOB is an O(N) allocator and is pretty poorly suited to running on > > anything like a modern desktop. Disallowing if SMP is probably > > reasonable, as even machines with multicore ARM or MIPS will probably > > have enough memory to make SLOB a bit painful. > > Ok. It's simple. This is fix. Are there any implications for preemptible kernels here? -- Mathematics is the supreme nostalgia of our time. -- 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: email@kvack.org