From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wi0-f180.google.com (mail-wi0-f180.google.com [209.85.212.180]) by kanga.kvack.org (Postfix) with ESMTP id 31DE190001D for ; Tue, 11 Nov 2014 21:07:16 -0500 (EST) Received: by mail-wi0-f180.google.com with SMTP id hi2so3440213wib.1 for ; Tue, 11 Nov 2014 18:07:15 -0800 (PST) Received: from jenni1.inet.fi (mta-out1.inet.fi. [62.71.2.203]) by mx.google.com with ESMTP id e17si25576755wiw.45.2014.11.11.18.07.15 for ; Tue, 11 Nov 2014 18:07:15 -0800 (PST) Date: Wed, 12 Nov 2014 04:07:03 +0200 From: "Kirill A. Shutemov" Subject: Re: [Bug 87891] New: kernel BUG at mm/slab.c:2625! Message-ID: <20141112020703.GC17446@node.dhcp.inet.fi> References: <20141111153120.9131c8e1459415afff8645bc@linux-foundation.org> <20141111164913.3616531c21c91499871c46de@linux-foundation.org> <20141112012241.GA17446@node.dhcp.inet.fi> <20141112014703.GB17446@node.dhcp.inet.fi> <20141111175603.ede86030.akpm@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20141111175603.ede86030.akpm@linux-foundation.org> Sender: owner-linux-mm@kvack.org List-ID: To: Andrew Morton Cc: Christoph Lameter , Ming Lei , Pekka Enberg , Joonsoo Kim , David Rientjes , Mel Gorman , Johannes Weiner , Pauli Nieminen , Dave Airlie , Tetsuo Handa , bugzilla-daemon@bugzilla.kernel.org, luke-jr+linuxbugs@utopios.org, dri-devel@lists.freedesktop.org, linux-mm@kvack.org On Tue, Nov 11, 2014 at 05:56:03PM -0800, Andrew Morton wrote: > On Wed, 12 Nov 2014 03:47:03 +0200 "Kirill A. Shutemov" wrote: > > > On Wed, Nov 12, 2014 at 03:22:41AM +0200, Kirill A. Shutemov wrote: > > > On Tue, Nov 11, 2014 at 04:49:13PM -0800, Andrew Morton wrote: > > > > On Tue, 11 Nov 2014 18:36:28 -0600 (CST) Christoph Lameter wrote: > > > > > > > > > On Tue, 11 Nov 2014, Andrew Morton wrote: > > > > > > > > > > > There's no point in doing > > > > > > > > > > > > #define GFP_SLAB_BUG_MASK (__GFP_DMA32|__GFP_HIGHMEM|~__GFP_BITS_MASK) > > > > > > > > > > > > because __GFP_DMA32|__GFP_HIGHMEM are already part of ~__GFP_BITS_MASK. > > > > > > > > > > ?? ~__GFP_BITS_MASK means bits 25 to 31 are set. > > > > > > > > > > __GFP_DMA32 is bit 2 and __GFP_HIGHMEM is bit 1. > > > > > > > > Ah, yes, OK. > > > > > > > > I suppose it's possible that __GFP_HIGHMEM was set. > > > > > > > > do_huge_pmd_anonymous_page > > > > ->pte_alloc_one > > > > ->alloc_pages(__userpte_alloc_gfp==__GFP_HIGHMEM) > > > > > > do_huge_pmd_anonymous_page > > > alloc_hugepage_vma > > > alloc_pages_vma(GFP_TRANSHUGE) > > > > > > GFP_TRANSHUGE contains GFP_HIGHUSER_MOVABLE, which has __GFP_HIGHMEM. > > > > Looks like it's reasonable to sanitize flags in shrink_slab() by dropping > > flags incompatible with slab expectation. Like this: > > > > diff --git a/mm/vmscan.c b/mm/vmscan.c > > index dcb47074ae03..eb165d29c5e5 100644 > > --- a/mm/vmscan.c > > +++ b/mm/vmscan.c > > @@ -369,6 +369,8 @@ unsigned long shrink_slab(struct shrink_control *shrinkctl, > > if (nr_pages_scanned == 0) > > nr_pages_scanned = SWAP_CLUSTER_MAX; > > > > + shrinkctl->gfp_mask &= ~(__GFP_DMA32 | __GFP_HIGHMEM); > > + > > if (!down_read_trylock(&shrinker_rwsem)) { > > /* > > * If we would return 0, our callers would understand that we > > Well no, because nobody is supposed to be passing this gfp_mask back > into a new allocation attempt anyway. It would be better to do > > shrinkctl->gfp_mask |= __GFP_IMMEDIATELY_GO_BUG; > > ? >>From my POV, the problem is that we combine what-need-to-be-freed gfp_mask with if-have-to-allocate gfp_mask: we want to respect __GFP_IO/FS on alloc, but not nessesary both if there's no restriction from the context. For shrink_slab(), __GFP_DMA32 and __GFP_HIGHMEM don't make sense in both cases. __GFP_IMMEDIATELY_GO_BUG would work too, but we also need to provide macros to construct alloc-suitable mask from the given one for yes-i-really-have-to-allocate case. -- Kirill A. Shutemov -- 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