From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf0-f179.google.com (mail-pf0-f179.google.com [209.85.192.179]) by kanga.kvack.org (Postfix) with ESMTP id C54F1828DF for ; Thu, 14 Jan 2016 23:47:08 -0500 (EST) Received: by mail-pf0-f179.google.com with SMTP id n128so111413091pfn.3 for ; Thu, 14 Jan 2016 20:47:08 -0800 (PST) Received: from lgeamrelo12.lge.com (LGEAMRELO12.lge.com. [156.147.23.52]) by mx.google.com with ESMTPS id 21si13845546pfl.36.2016.01.14.20.47.07 for (version=TLS1 cipher=ECDHE-RSA-AES128-SHA bits=128/128); Thu, 14 Jan 2016 20:47:07 -0800 (PST) Date: Fri, 15 Jan 2016 13:49:16 +0900 From: Minchan Kim Subject: Re: [PATCH] zsmalloc: fix migrate_zspage-zs_free race condition Message-ID: <20160115044916.GB11203@bbox> References: <1452818184-2994-1-git-send-email-junil0814.lee@lge.com> <20160115023518.GA10843@bbox> <20160115032712.GC1993@swordfish> MIME-Version: 1.0 In-Reply-To: <20160115032712.GC1993@swordfish> Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline Sender: owner-linux-mm@kvack.org List-ID: To: Sergey Senozhatsky Cc: Junil Lee , Andrew Morton , ngupta@vflare.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org On Fri, Jan 15, 2016 at 12:27:12PM +0900, Sergey Senozhatsky wrote: > Cc Andrew, > > On (01/15/16 11:35), Minchan Kim wrote: > [..] > > > Signed-off-by: Junil Lee > > > --- > > > mm/zsmalloc.c | 1 + > > > 1 file changed, 1 insertion(+) > > > > > > diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c > > > index e7414ce..bb459ef 100644 > > > --- a/mm/zsmalloc.c > > > +++ b/mm/zsmalloc.c > > > @@ -1635,6 +1635,7 @@ static int migrate_zspage(struct zs_pool *pool, struct size_class *class, > > > free_obj = obj_malloc(d_page, class, handle); > > > zs_object_copy(free_obj, used_obj, class); > > > index++; > > > + free_obj |= BIT(HANDLE_PIN_BIT); > > > record_obj(handle, free_obj); > > > > I think record_obj should store free_obj to *handle with masking off least bit. > > IOW, how about this? > > > > record_obj(handle, obj) > > { > > *(unsigned long)handle = obj & ~(1< > } > > [just a wild idea] > > or zs_free() can take spin_lock(&class->lock) earlier, it cannot free the Earlier? What do you mean? For getting right class, we should get a stable handle so we couldn't get class lock first than handle lock. If I misunderstand, please elaborate a bit. > object until the class is locked anyway, and migration is happening with > the locked class. extending class->lock scope in zs_free() thus should > not affect the perfomance. so it'll be either zs_free() is touching the > object or the migration, not both. > > -ss -- 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