Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1161091AbaKNPHi (ORCPT ); Fri, 14 Nov 2014 10:07:38 -0500 Received: from relay.variantweb.net ([104.131.199.242]:53840 "EHLO relay.variantweb.net" rhost-flags-OK-FAIL-OK-FAIL) by vger.kernel.org with ESMTP id S935367AbaKNPHg (ORCPT ); Fri, 14 Nov 2014 10:07:36 -0500 Date: Fri, 14 Nov 2014 09:07:32 -0600 From: Seth Jennings To: Minchan Kim Cc: 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: <20141114150732.GA2402@cerebellum.variantweb.net> References: <1415927461-14220-1-git-send-email-minchan@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1415927461-14220-1-git-send-email-minchan@kernel.org> 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 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: --- 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. 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