Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933612AbcJLOao (ORCPT ); Wed, 12 Oct 2016 10:30:44 -0400 Received: from sender153-mail.zoho.com ([74.201.84.153]:25410 "EHLO sender153-mail.zoho.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933184AbcJLOaf (ORCPT ); Wed, 12 Oct 2016 10:30:35 -0400 DomainKey-Signature: a=rsa-sha1; q=dns; c=nofws; s=zapps768; d=zoho.com; h=cc:to:from:subject:message-id:date:user-agent:mime-version:content-type; b=CbeXmDU93oDz8/gLcmR4TlVkkk4keoojkvGXsHp0np8fC98mUMVBxrtkeyfFK79/3ZXLwca17boF NF/LrnWwAY4hRRuCKbnMC24zADOqtIlS8QrkfMl02q2nLRpc22zY Cc: zijun_hu@htc.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org To: akpm@linux-foundation.org, mhocko@kernel.org, rientjes@google.com, tj@kernel.org, sfr@canb.auug.org.au, mingo@kernel.org, iamjoonsoo.kim@lge.com, mgorman@techsingularity.net, hannes@cmpxchg.org, chris@chris-wilson.co.uk, vdavydov.dev@gmail.com From: zijun_hu Subject: [RFC PATCH 1/1] mm/vmalloc.c: correct logic errors when insert vmap_area Message-ID: Date: Wed, 12 Oct 2016 22:30:13 +0800 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:45.0) Gecko/20100101 Thunderbird/45.3.0 MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2411 Lines: 65 From: zijun_hu the KVA allocator organizes vmap_areas allocated by rbtree. in order to insert a new vmap_area @i_va into the rbtree, walk around the rbtree from root and compare the vmap_area @t_va met on the rbtree against @i_va; walk toward the left branch of @t_va if @i_va is lower than @t_va, and right branch if higher, otherwise handle this error case since @i_va has overlay with @t_va; however, __insert_vmap_area() don't follow the desired procedure rightly, moreover, it includes a meaningless else if condition and a redundant else branch as shown by comments in below code segments: static void __insert_vmap_area(struct vmap_area *va) { as a internal interface parameter, we assume vmap_area @va has nonzero size ... if (va->va_start < tmp->va_end) p = &(*p)->rb_left; else if (va->va_end > tmp->va_start) p = &(*p)->rb_right; this else if condition is always true and meaningless due to va->va_end > va->va_start >= tmp_va->va_end > tmp_va->va_start normally else BUG(); this BUG() is meaningless too due to never be reached normally ... } it looks like the else if condition and else branch are canceled. no errors are caused since the vmap_area @va to insert as a internal interface parameter doesn't have overlay with any one on the rbtree normally. however __insert_vmap_area() looks weird and really has several logic errors as pointed out above when it is viewed as a separate function. fix by walking around vmap_area rbtree as described above to insert a vmap_area. BTW, (va->va_end == tmp_va->va_start) is consider as legal case since it indicates vmap_area @va left neighbors with @tmp_va tightly. Fixes: db64fe02258f ("mm: rewrite vmap layer") Signed-off-by: zijun_hu --- mm/vmalloc.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/mm/vmalloc.c b/mm/vmalloc.c index 5daf3211b84f..8b80931654b7 100644 --- a/mm/vmalloc.c +++ b/mm/vmalloc.c @@ -321,10 +321,10 @@ static void __insert_vmap_area(struct vmap_area *va) parent = *p; tmp_va = rb_entry(parent, struct vmap_area, rb_node); - if (va->va_start < tmp_va->va_end) - p = &(*p)->rb_left; - else if (va->va_end > tmp_va->va_start) - p = &(*p)->rb_right; + if (va->va_end <= tmp_va->va_start) + p = &parent->rb_left; + else if (va->va_start >= tmp_va->va_end) + p = &parent->rb_right; else BUG(); } -- 1.9.1