From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx128.postini.com [74.125.245.128]) by kanga.kvack.org (Postfix) with SMTP id 8868F6B0075 for ; Thu, 1 Nov 2012 19:03:44 -0400 (EDT) Received: by mail-ie0-f169.google.com with SMTP id 10so5317236ied.14 for ; Thu, 01 Nov 2012 16:03:43 -0700 (PDT) Date: Thu, 1 Nov 2012 16:03:40 -0700 (PDT) From: Hugh Dickins Subject: Re: shmem_getpage_gfp VM_BUG_ON triggered. [3.7rc2] In-Reply-To: <20121101191052.GA5884@redhat.com> Message-ID: References: <20121025023738.GA27001@redhat.com> <20121101191052.GA5884@redhat.com> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-linux-mm@kvack.org List-ID: To: Dave Jones Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org On Thu, 1 Nov 2012, Dave Jones wrote: > On Wed, Oct 24, 2012 at 09:36:27PM -0700, Hugh Dickins wrote: > > On Wed, 24 Oct 2012, Dave Jones wrote: > > > > > Machine under significant load (4gb memory used, swap usage fluctuating) > > > triggered this... > > > > > > WARNING: at mm/shmem.c:1151 shmem_getpage_gfp+0xa5c/0xa70() > > > > > > 1148 error = shmem_add_to_page_cache(page, mapping, index, > > > 1149 gfp, swp_to_radix_entry(swap)); > > > 1150 /* We already confirmed swap, and make no allocation */ > > > 1151 VM_BUG_ON(error); > > > 1152 } > > > > That's very surprising. Easy enough to handle an error there, but > > of course I made it a VM_BUG_ON because it violates my assumptions: > > I rather need to understand how this can be, and I've no idea. > > I just noticed we had a user report hitting this same warning, but > with a different trace.. > > : [] warn_slowpath_common+0x7f/0xc0 > : [] warn_slowpath_null+0x1a/0x20 > : [] shmem_getpage_gfp+0x7f3/0x830 > : [] ? vma_adjust+0x3ed/0x620 > : [] shmem_file_aio_read+0x1f2/0x380 > : [] do_sync_read+0xa7/0xe0 > : [] vfs_read+0xa9/0x180 > : [] sys_read+0x4a/0x90 > : [] system_call_fastpath+0x16/0x1b Equally explicable by Hannes's hypothesis; but useful supporting evidence, thank you. Except... earlier in the thread you explained how you hacked #define VM_BUG_ON(cond) WARN_ON(cond) to get this to come out as a warning instead of a bug, and now it looks as if "a user" has here done the same. Which is very much a user's right, of course; but does make me wonder whether that user might actually be davej ;) Never mind, whatever, it's more justification for the fix - which I've honestly not forgotten, but somehow not got around to sending (with a couple of others even longer outstanding). On its way shortly, for some unpredictable value of shortly. Hugh -- 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