From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754829Ab2GJPT3 (ORCPT ); Tue, 10 Jul 2012 11:19:29 -0400 Received: from e8.ny.us.ibm.com ([32.97.182.138]:50256 "EHLO e8.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752954Ab2GJPT2 (ORCPT ); Tue, 10 Jul 2012 11:19:28 -0400 Message-ID: <4FFC478C.4050505@linux.vnet.ibm.com> Date: Tue, 10 Jul 2012 10:17:32 -0500 From: Seth Jennings User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:13.0) Gecko/20120615 Thunderbird/13.0.1 MIME-Version: 1.0 To: Minchan Kim CC: Greg Kroah-Hartman , Andrew Morton , Dan Magenheimer , Konrad Rzeszutek Wilk , Nitin Gupta , Robert Jennings , linux-mm@kvack.org, devel@driverdev.osuosl.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 3/4] zsmalloc: add details to zs_map_object boiler plate References: <1341263752-10210-1-git-send-email-sjenning@linux.vnet.ibm.com> <1341263752-10210-4-git-send-email-sjenning@linux.vnet.ibm.com> <4FFB94FF.8030401@kernel.org> In-Reply-To: <4FFB94FF.8030401@kernel.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Content-Scanned: Fidelis XPS MAILER x-cbid: 12071015-9360-0000-0000-000008436BC9 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 07/09/2012 09:35 PM, Minchan Kim wrote: > On 07/03/2012 06:15 AM, Seth Jennings wrote: >> Add information on the usage limits of zs_map_object() >> >> Signed-off-by: Seth Jennings >> --- >> drivers/staging/zsmalloc/zsmalloc-main.c | 7 ++++++- >> 1 file changed, 6 insertions(+), 1 deletion(-) >> >> diff --git a/drivers/staging/zsmalloc/zsmalloc-main.c b/drivers/staging/zsmalloc/zsmalloc-main.c >> index 4942d41..abf7c13 100644 >> --- a/drivers/staging/zsmalloc/zsmalloc-main.c >> +++ b/drivers/staging/zsmalloc/zsmalloc-main.c >> @@ -747,7 +747,12 @@ EXPORT_SYMBOL_GPL(zs_free); >> * >> * Before using an object allocated from zs_malloc, it must be mapped using >> * this function. When done with the object, it must be unmapped using >> - * zs_unmap_object >> + * zs_unmap_object. >> + * >> + * Only one object can be mapped per cpu at a time. There is no protection >> + * against nested mappings. >> + * >> + * This function returns with preemption and page faults disabled. >> */ >> void *zs_map_object(struct zs_pool *pool, unsigned long handle) >> { >> > > The comment is good but I hope we can detect it automatically with DEBUG > option. It wouldn't be hard but it's a debug patch so not critical > until we receive some report about the bug. Yes, we could implement some detection scheme later. > > The possibility for nesting is that it is used by irq context. > > A uses the mapping > . > . > . > IRQ happen > B uses the mapping in IRQ context > . > . > . > > Maybe we need local_irq_save/restore in zs_[un]map_object path. I'd rather not disable interrupts since that will create unnecessary interrupt latency for all users, even if they don't need interrupt protection. If a particular user uses zs_map_object() in an interrupt path, it will be up to that user to disable interrupts to ensure safety. Thanks, Seth