From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754019AbaKONUM (ORCPT ); Sat, 15 Nov 2014 08:20:12 -0500 Received: from mail-pd0-f175.google.com ([209.85.192.175]:46374 "EHLO mail-pd0-f175.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752401AbaKONUJ (ORCPT ); Sat, 15 Nov 2014 08:20:09 -0500 Date: Sat, 15 Nov 2014 22:20:30 +0900 From: Sergey Senozhatsky To: Seth Jennings Cc: Minchan Kim , Andrew Morton , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Nitin Gupta , Sergey Senozhatsky , Dan Streetman , Jerome Marchand Subject: Re: [PATCH] zsmalloc: correct fragile [kmap|kunmap]_atomic use Message-ID: <20141115132030.GB1046@swordfish> References: <1415927461-14220-1-git-send-email-minchan@kernel.org> <20141114150732.GA2402@cerebellum.variantweb.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20141114150732.GA2402@cerebellum.variantweb.net> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On (11/14/14 09:07), Seth Jennings wrote: > On Fri, Nov 14, 2014 at 10:11:01AM +0900, Minchan Kim wrote: > > The kunmap_atomic should use virtual address getting by kmap_atomic. > > However, some pieces of code in zsmalloc uses modified address, > > not the one got by kmap_atomic for kunmap_atomic. > > > > It's okay for working because zsmalloc modifies the address > > inner PAGE_SIZE bounday so it works with current kmap_atomic's > > implementation. But it's still fragile with potential changing > > of kmap_atomic so let's correct it. > > Seems like you could just use PAGE_MASK to get the base page address > from link like this: > both solutions look good to me: Acked-by: Sergey Senozhatsky -ss > --- > diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c > index b3b57ef..d6ca05a 100644 > --- a/mm/zsmalloc.c > +++ b/mm/zsmalloc.c > @@ -654,7 +654,7 @@ static void init_zspage(struct page *first_page, struct size_class *class) > */ > next_page = get_next_page(page); > link->next = obj_location_to_handle(next_page, 0); > - kunmap_atomic(link); > + kunmap_atomic((void *)((unsigned long)link & PAGE_MASK)); > page = next_page; > off %= PAGE_SIZE; > } > @@ -1087,7 +1087,7 @@ unsigned long zs_malloc(struct zs_pool *pool, size_t size) > m_offset / sizeof(*link); > first_page->freelist = link->next; > memset(link, POISON_INUSE, sizeof(*link)); > - kunmap_atomic(link); > + kunmap_atomic((void *)((unsigned long)link & PAGE_MASK)); > > first_page->inuse++; > /* Now move the zspage to another fullness group, if required */ > @@ -1124,7 +1124,7 @@ void zs_free(struct zs_pool *pool, unsigned long obj) > link = (struct link_free *)((unsigned char *)kmap_atomic(f_page) > + f_offset); > link->next = first_page->freelist; > - kunmap_atomic(link); > + kunmap_atomic((void *)((unsigned long)link & PAGE_MASK)); > first_page->freelist = (void *)obj; > > first_page->inuse--; > --- > > This seems cleaner, but, at the same time, it isn't obvious that we are > passing the same value to kunmap_atomic() that we got from > kmap_atomic(). Just a thought. > > Either way: > > Reviewed-by: Seth Jennings > > > > > Signed-off-by: Minchan Kim > > --- > > mm/zsmalloc.c | 21 ++++++++++++--------- > > 1 file changed, 12 insertions(+), 9 deletions(-) > > > > diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c > > index b3b57ef85830..85e14f584048 100644 > > --- a/mm/zsmalloc.c > > +++ b/mm/zsmalloc.c > > @@ -629,6 +629,7 @@ static void init_zspage(struct page *first_page, struct size_class *class) > > struct page *next_page; > > struct link_free *link; > > unsigned int i = 1; > > + void *vaddr; > > > > /* > > * page->index stores offset of first object starting > > @@ -639,8 +640,8 @@ static void init_zspage(struct page *first_page, struct size_class *class) > > if (page != first_page) > > page->index = off; > > > > - link = (struct link_free *)kmap_atomic(page) + > > - off / sizeof(*link); > > + vaddr = kmap_atomic(page); > > + link = (struct link_free *)vaddr + off / sizeof(*link); > > > > while ((off += class->size) < PAGE_SIZE) { > > link->next = obj_location_to_handle(page, i++); > > @@ -654,7 +655,7 @@ static void init_zspage(struct page *first_page, struct size_class *class) > > */ > > next_page = get_next_page(page); > > link->next = obj_location_to_handle(next_page, 0); > > - kunmap_atomic(link); > > + kunmap_atomic(vaddr); > > page = next_page; > > off %= PAGE_SIZE; > > } > > @@ -1055,6 +1056,7 @@ unsigned long zs_malloc(struct zs_pool *pool, size_t size) > > unsigned long obj; > > struct link_free *link; > > struct size_class *class; > > + void *vaddr; > > > > struct page *first_page, *m_page; > > unsigned long m_objidx, m_offset; > > @@ -1083,11 +1085,11 @@ unsigned long zs_malloc(struct zs_pool *pool, size_t size) > > obj_handle_to_location(obj, &m_page, &m_objidx); > > m_offset = obj_idx_to_offset(m_page, m_objidx, class->size); > > > > - link = (struct link_free *)kmap_atomic(m_page) + > > - m_offset / sizeof(*link); > > + vaddr = kmap_atomic(m_page); > > + link = (struct link_free *)vaddr + m_offset / sizeof(*link); > > first_page->freelist = link->next; > > memset(link, POISON_INUSE, sizeof(*link)); > > - kunmap_atomic(link); > > + kunmap_atomic(vaddr); > > > > first_page->inuse++; > > /* Now move the zspage to another fullness group, if required */ > > @@ -1103,6 +1105,7 @@ void zs_free(struct zs_pool *pool, unsigned long obj) > > struct link_free *link; > > struct page *first_page, *f_page; > > unsigned long f_objidx, f_offset; > > + void *vaddr; > > > > int class_idx; > > struct size_class *class; > > @@ -1121,10 +1124,10 @@ void zs_free(struct zs_pool *pool, unsigned long obj) > > spin_lock(&class->lock); > > > > /* Insert this object in containing zspage's freelist */ > > - link = (struct link_free *)((unsigned char *)kmap_atomic(f_page) > > - + f_offset); > > + vaddr = kmap_atomic(f_page); > > + link = (struct link_free *)(vaddr + f_offset); > > link->next = first_page->freelist; > > - kunmap_atomic(link); > > + kunmap_atomic(vaddr); > > first_page->freelist = (void *)obj; > > > > first_page->inuse--; > > -- > > 2.0.0 > > > > -- > > 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 >