From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934212AbZIOCC2 (ORCPT ); Mon, 14 Sep 2009 22:02:28 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S934209AbZIOCCX (ORCPT ); Mon, 14 Sep 2009 22:02:23 -0400 Received: from mga03.intel.com ([143.182.124.21]:38880 "EHLO mga03.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S934208AbZIOCCW (ORCPT ); Mon, 14 Sep 2009 22:02:22 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.44,386,1249282800"; d="scan'208";a="187616632" Date: Tue, 15 Sep 2009 10:02:08 +0800 From: Wu Fengguang To: KAMEZAWA Hiroyuki Cc: Andrew Morton , "mtosatti@redhat.com" , "gregkh@suse.de" , "broonie@opensource.wolfsonmicro.com" , "johannes@sipsolutions.net" , "avi@qumranet.com" , "andi@firstfloor.org" , "linux-kernel@vger.kernel.org" , WANG Cong , Mike Smith , Nick Piggin Subject: Re: [PATCH] devmem: handle partial kmem write/read Message-ID: <20090915020208.GA15159@localhost> References: <20090914032901.GA16189@localhost> <20090914043444.GA18590@localhost> <20090915092448.d511df31.kamezawa.hiroyu@jp.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20090915092448.d511df31.kamezawa.hiroyu@jp.fujitsu.com> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Sep 15, 2009 at 08:24:48AM +0800, KAMEZAWA Hiroyuki wrote: > On Mon, 14 Sep 2009 12:34:44 +0800 > Wu Fengguang wrote: > > > Hi Kame, > > > > This patch needs more work. I first intent to fix a bug: > > > > sz = vwrite(kbuf, (char *)p, sz); > > p += sz; > > } > > > > So if the returned len is 0, the kbuf/p pointers will mismatch. > > > > Then I realize it changed the write behavior. The current vwrite() > > behavior is strange, it returns 0 if _whole range_ is hole, otherwise > > ignores the hole silently. So holes can be treated differently even in > > the original code. > > > Ah, ok... > > > I'm not really sure about the right behavior. KAME-san, do you have > > any suggestions? > > > maybe following make sense. > = > written = vwrite(kbuf, (char *p), sz); > if (!written) // whole vmem was a hole > written = sz; Since the 0 return value won't be used at all, it would be simpler to tell vwrite() return the untouched buflen/sz, like this. It will ignore _all_ the holes silently. Need to update comments too. --- linux-mm.orig/mm/vmalloc.c 2009-09-15 09:40:08.000000000 +0800 +++ linux-mm/mm/vmalloc.c 2009-09-15 09:43:33.000000000 +0800 @@ -1834,7 +1834,6 @@ long vwrite(char *buf, char *addr, unsig struct vm_struct *tmp; char *vaddr; unsigned long n, buflen; - int copied = 0; /* Don't allow overflow */ if ((unsigned long) addr + count < count) @@ -1858,7 +1857,6 @@ long vwrite(char *buf, char *addr, unsig n = count; if (!(tmp->flags & VM_IOREMAP)) { aligned_vwrite(buf, addr, n); - copied++; } buf += n; addr += n; @@ -1866,8 +1864,6 @@ long vwrite(char *buf, char *addr, unsig } finished: read_unlock(&vmlist_lock); - if (!copied) - return 0; return buflen; } > == > needs fix. > > Anyway, I wonder kmem is broken. It's should be totally rewritten. > > For example, this doesn't check anything. > == > if (p < (unsigned long) high_memory) { > > == > > But....are there users ? > If necessary, I'll write some... I'm trying to stop possible mem/kmem users to access hwpoison pages.. I'm not the user, but rather a tester ;) Thanks, Fengguang > Thanks, > -Kame > > > > Thanks, > > Fengguang > > > > On Mon, Sep 14, 2009 at 11:29:01AM +0800, Wu Fengguang wrote: > > > Current vwrite silently ignores vwrite() to vmap holes. > > > Better behavior should be stop the write and return > > > on such holes. > > > > > > Also return on partial read, which may happen in future > > > (eg. hit hwpoison pages). > > > > > > CC: Andi Kleen > > > Signed-off-by: Wu Fengguang > > > --- > > > drivers/char/mem.c | 30 ++++++++++++++++++------------ > > > 1 file changed, 18 insertions(+), 12 deletions(-) > > > > > > --- linux-mm.orig/drivers/char/mem.c 2009-09-14 10:59:50.000000000 +0800 > > > +++ linux-mm/drivers/char/mem.c 2009-09-14 11:06:25.000000000 +0800 > > > @@ -444,18 +444,22 @@ static ssize_t read_kmem(struct file *fi > > > if (!kbuf) > > > return -ENOMEM; > > > while (count > 0) { > > > + unsigned long n; > > > + > > > sz = size_inside_page(p, count); > > > - sz = vread(kbuf, (char *)p, sz); > > > - if (!sz) > > > + n = vread(kbuf, (char *)p, sz); > > > + if (!n) > > > break; > > > - if (copy_to_user(buf, kbuf, sz)) { > > > + if (copy_to_user(buf, kbuf, n)) { > > > free_page((unsigned long)kbuf); > > > return -EFAULT; > > > } > > > - count -= sz; > > > - buf += sz; > > > - read += sz; > > > - p += sz; > > > + count -= n; > > > + buf += n; > > > + read += n; > > > + p += n; > > > + if (n < sz) > > > + break; > > > } > > > free_page((unsigned long)kbuf); > > > } > > > @@ -551,11 +555,13 @@ static ssize_t write_kmem(struct file * > > > free_page((unsigned long)kbuf); > > > return -EFAULT; > > > } > > > - sz = vwrite(kbuf, (char *)p, sz); > > > - count -= sz; > > > - buf += sz; > > > - virtr += sz; > > > - p += sz; > > > + n = vwrite(kbuf, (char *)p, sz); > > > + count -= n; > > > + buf += n; > > > + virtr += n; > > > + p += n; > > > + if (n < sz) > > > + break; > > > } > > > free_page((unsigned long)kbuf); > > > } > > -- > > 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/ > >