Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932482Ab3ICHla (ORCPT ); Tue, 3 Sep 2013 03:41:30 -0400 Received: from LGEMRELSE1Q.lge.com ([156.147.1.111]:42836 "EHLO LGEMRELSE1Q.lge.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1759308Ab3ICHl3 (ORCPT ); Tue, 3 Sep 2013 03:41:29 -0400 X-AuditID: 9c93016f-b7cf0ae00000518f-94-522592a70c7e Date: Tue, 3 Sep 2013 16:42:21 +0900 From: Joonsoo Kim To: Wanpeng Li Cc: Andrew Morton , David Rientjes , KOSAKI Motohiro , Zhang Yanfei , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v4 4/4] mm/vmalloc: don't assume vmap_area w/o VM_VM_AREA flag is vm_map_ram allocation Message-ID: <20130903074221.GA30920@lge.com> References: <1378191706-29696-1-git-send-email-liwanp@linux.vnet.ibm.com> <1378191706-29696-4-git-send-email-liwanp@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1378191706-29696-4-git-send-email-liwanp@linux.vnet.ibm.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-Brightmail-Tracker: AAAAAA== Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2339 Lines: 71 On Tue, Sep 03, 2013 at 03:01:46PM +0800, Wanpeng Li wrote: > There is a race window between vmap_area free and show vmap_area information. > > A B > > remove_vm_area > spin_lock(&vmap_area_lock); > va->flags &= ~VM_VM_AREA; > spin_unlock(&vmap_area_lock); > spin_lock(&vmap_area_lock); > if (va->flags & (VM_LAZY_FREE | VM_LAZY_FREEZING)) > return 0; > if (!(va->flags & VM_VM_AREA)) { > seq_printf(m, "0x%pK-0x%pK %7ld vm_map_ram\n", > (void *)va->va_start, (void *)va->va_end, > va->va_end - va->va_start); > return 0; > } > free_unmap_vmap_area(va); > flush_cache_vunmap > free_unmap_vmap_area_noflush > unmap_vmap_area > free_vmap_area_noflush > va->flags |= VM_LAZY_FREE > > The assumption is introduced by commit: d4033afd(mm, vmalloc: iterate vmap_area_list, > instead of vmlist, in vmallocinfo()). This patch fix it by drop the assumption and > keep not dump vm_map_ram allocation information as the logic before that commit. > > Signed-off-by: Wanpeng Li > --- > mm/vmalloc.c | 7 ------- > 1 file changed, 7 deletions(-) > > diff --git a/mm/vmalloc.c b/mm/vmalloc.c > index 5368b17..62b7932 100644 > --- a/mm/vmalloc.c > +++ b/mm/vmalloc.c > @@ -2586,13 +2586,6 @@ static int s_show(struct seq_file *m, void *p) > if (va->flags & (VM_LAZY_FREE | VM_LAZY_FREEING)) > return 0; > > - if (!(va->flags & VM_VM_AREA)) { > - seq_printf(m, "0x%pK-0x%pK %7ld vm_map_ram\n", > - (void *)va->va_start, (void *)va->va_end, > - va->va_end - va->va_start); > - return 0; > - } > - > v = va->vm; > > seq_printf(m, "0x%pK-0x%pK %7ld", Hello, Wanpeng. Did you test this patch? I guess that, With this patch, if there are some vm_map areas, null pointer deference would occurs, since va->vm may be null for it. And with this patch, if this race really occur, null pointer deference would occurs too, since va->vm is set to null in remove_vm_area(). I think that this is not a right fix for this possible race. Thanks. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/