Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755274AbaKPLlk (ORCPT ); Sun, 16 Nov 2014 06:41:40 -0500 Received: from mail-oi0-f48.google.com ([209.85.218.48]:62636 "EHLO mail-oi0-f48.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755005AbaKPLli (ORCPT ); Sun, 16 Nov 2014 06:41:38 -0500 MIME-Version: 1.0 In-Reply-To: <1415927461-14220-1-git-send-email-minchan@kernel.org> References: <1415927461-14220-1-git-send-email-minchan@kernel.org> Date: Sun, 16 Nov 2014 19:41:37 +0800 Message-ID: Subject: Re: [PATCH] zsmalloc: correct fragile [kmap|kunmap]_atomic use From: Ganesh Mahendran To: Minchan Kim Cc: Andrew Morton , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Nitin Gupta , Sergey Senozhatsky , Dan Streetman , Seth Jennings , Jerome Marchand Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hello 2014-11-14 9:11 GMT+08:00 Minchan Kim : > 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. > > 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); Just a nitpick: I think link = (struct link_free *)(vaddr + off); is better. To use the same method as in zs_free() link = (struct link_free *)(vaddr + f_offset); > > 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); link = (struct link_free *)(vaddr + m_offset) > 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); Yes, I think this method to calc *link* is better. (: Thanks > link->next = first_page->freelist; > - kunmap_atomic(link); > + kunmap_atomic(vaddr); > first_page->freelist = (void *)obj; > > first_page->inuse--; > -- > 2.0.0 > > -- > 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/ -- 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/