From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1763597AbXK2VfJ (ORCPT ); Thu, 29 Nov 2007 16:35:09 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1760503AbXK2Vez (ORCPT ); Thu, 29 Nov 2007 16:34:55 -0500 Received: from waste.org ([66.93.16.53]:39375 "EHLO waste.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1762273AbXK2Vey (ORCPT ); Thu, 29 Nov 2007 16:34:54 -0500 Date: Thu, 29 Nov 2007 15:32:18 -0600 From: Matt Mackall To: Ingo Molnar Cc: linux-kernel@vger.kernel.org, Andrew Morton , "David S. Miller" , Allan Stephens , Jon Paul Maloy Subject: Re: [bug] SLOB, tipc_init(), WARNING: at arch/x86/mm/highmem_32.c:52 kmap_atomic_prot() Message-ID: <20071129213217.GW19691@waste.org> References: <20071129142546.GA27719@elte.hu> <20071129143920.GA32146@elte.hu> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20071129143920.GA32146@elte.hu> User-Agent: Mutt/1.5.13 (2006-08-11) Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Nov 29, 2007 at 03:39:20PM +0100, Ingo Molnar wrote: > > * Ingo Molnar wrote: > > > i'm getting this on 32-bit (with the kmap-atomic debugging patch > > applied): > > > > ----------------> > > Calling initcall 0x78b67c00: tipc_init+0x0/0xc0() > > TIPC: Activated (version 1.6.2 compiled Nov 29 2007 15:04:36) > > WARNING: at arch/x86/mm/highmem_32.c:52 kmap_atomic_prot() > > Pid: 1, comm: swapper Not tainted 2.6.24-rc3-cfs-v24 #45 > > [<78107272>] show_trace_log_lvl+0x12/0x40 > > [<781072ad>] show_trace+0xd/0x20 > > [<781086f8>] dump_stack+0x58/0x60 > > [<7811541f>] kmap_atomic_prot+0x1bf/0x240 > > [<781154ae>] kmap_atomic+0xe/0x20 > > [<78157be5>] get_page_from_freelist+0x225/0x420 > > [<78157e4d>] __alloc_pages+0x6d/0x3a0 > > [<78169a7b>] slob_new_page+0x1b/0x60 > > [<78169be4>] slob_alloc+0x124/0x1e0 > > [<78169e0f>] __kmalloc_node+0x6f/0xa0 > > [<7884f7c2>] reg_init+0x42/0x80 > > [<7884f80a>] tipc_reg_start+0xa/0x40 > > [<7883e6c6>] tipc_core_start+0x66/0xc0 > > [<78b67c81>] tipc_init+0x81/0xc0 > > this is due to the kzalloc() here: > > 0x7884f1d0 is in reg_init (net/tipc/user_reg.c:88). > 83 spin_lock_bh(®_lock); > 84 if (!users) { > 85 users = kzalloc(USER_LIST_SIZE, GFP_ATOMIC); > 86 if (users) { > 87 for (i = 1; i <= MAX_USERID; i++) { > 88 users[i].next = i - 1; > > which does a: > > 120 static inline void clear_highpage(struct page *page) > 121 { > 122 void *kaddr = kmap_atomic(page, KM_USER0); > 123 clear_page(kaddr); > 124 kunmap_atomic(kaddr, KM_USER0); > 125 } > > but ... why does the debug code think it's in softirq context? > > plus, and this is a slob question i guess, how come we drop into > clear_highpage() for a kzalloc()?? Good question. Looks like kzalloc switched from doing a memset to passing a GFP_ZERO flag down to kmalloc. Slob didn't get completely updated to reflect this, so it blindly propagates the flag onto __alloc_pages and does a harmless double-clear. Someone should remind us what the point of moving the kzalloc memset down into the allocators was. We now have all three allocators doing: if (unlikely((flags & __GFP_ZERO) && ptr)) memset(ptr, 0, obj_size(cachep)); and needing to mask flags before passing them to page allocators, which hardly seems better than kzalloc unconditionally doing the memset. Wouldn't it be better/faster/smaller to make kzalloc a non-inline? Slob also has a nice second path for large kmallocs where it just calls the page allocator directly which also needs this treatment. Which does the right thing with non-highmem systems, but can hit this bug otherwise. Below is a totally untested patch. Alternately, we could simply tweak clear_highpage to remove the limitation, but that would leave slob doing an extra clear. diff -r c60016ba6237 mm/slob.c --- a/mm/slob.c Tue Nov 13 09:09:36 2007 -0800 +++ b/mm/slob.c Thu Nov 29 15:15:54 2007 -0600 @@ -223,6 +231,7 @@ static void *slob_new_page(gfp_t gfp, in { void *page; + gfp &= ~__GFP_ZERO; #ifdef CONFIG_NUMA if (node != -1) page = alloc_pages_node(node, gfp, order); @@ -457,6 +470,8 @@ void *__kmalloc_node(size_t size, gfp_t page = virt_to_page(ret); page->private = size; } + if (unlikely((gfp & __GFP_ZERO) && ret)) + memset(ret, 0, size); return ret; } } -- Mathematics is the supreme nostalgia of our time.