From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ed1-f71.google.com (mail-ed1-f71.google.com [209.85.208.71]) by kanga.kvack.org (Postfix) with ESMTP id 08A676B44A6 for ; Mon, 26 Nov 2018 19:18:30 -0500 (EST) Received: by mail-ed1-f71.google.com with SMTP id q8so4694105edd.8 for ; Mon, 26 Nov 2018 16:18:29 -0800 (PST) Received: from mail-sor-f65.google.com (mail-sor-f65.google.com. [209.85.220.65]) by mx.google.com with SMTPS id n56sor1548100edn.7.2018.11.26.16.18.28 for (Google Transport Security); Mon, 26 Nov 2018 16:18:28 -0800 (PST) Date: Tue, 27 Nov 2018 00:18:26 +0000 From: Wei Yang Subject: Re: [PATCH] mm, hotplug: protect nr_zones with pgdat_resize_lock() Message-ID: <20181127001826.vek2rkbivoygy6pq@master> Reply-To: Wei Yang References: <20181120014822.27968-1-richard.weiyang@gmail.com> <20181120073141.GY22247@dhcp22.suse.cz> <3ba8d8c524d86af52e4c1fddc2d45734@suse.de> <20181121025231.ggk7zgq53nmqsqds@master> <20181121071549.GG12932@dhcp22.suse.cz> <20181126081608.GE12455@dhcp22.suse.cz> <20181126090654.hgazohtksychaaf3@master> <20181126100330.GF12455@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181126100330.GF12455@dhcp22.suse.cz> Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko Cc: Wei Yang , Oscar Salvador , Andrew Morton , Linux-MM On Mon, Nov 26, 2018 at 11:03:30AM +0100, Michal Hocko wrote: >On Mon 26-11-18 09:06:54, Wei Yang wrote: >> On Mon, Nov 26, 2018 at 09:16:08AM +0100, Michal Hocko wrote: >> >On Mon 26-11-18 10:28:40, Wei Yang wrote: >> >[...] >> >> But I get some difficulty to understand this TODO. You want to get rid of >> >> these lock? While these locks seem necessary to protect those data of >> >> pgdat/zone. Would you mind sharing more on this statement? >> > >> >Why do we need this lock to be irqsave? Is there any caller that uses >> >the lock from the IRQ context? >> >> I see you put the comment 'irqsave' in code, I thought this is the >> requirement bringing in by this commit. So this is copyed from somewhere >> else? > >No, the irqsave lock has been there for a long time but it was not clear >to me whether it is still required. Maybe it never was. I just didn't >have time to look into that and put a TODO there. The code wouldn't be >less correct if I kept it. > Let me summarize what you expect to do. Go through all the users of pgdat_resize_lock, if none of them is called from IRQ context, we could do the following change: diff --git a/include/linux/memory_hotplug.h b/include/linux/memory_hotplug.h index ffd9cd10fcf3..45a5affcab8a 100644 --- a/include/linux/memory_hotplug.h +++ b/include/linux/memory_hotplug.h @@ -272,14 +272,14 @@ static inline bool movable_node_is_enabled(void) * pgdat resizing functions */ static inline -void pgdat_resize_lock(struct pglist_data *pgdat, unsigned long *flags) +void pgdat_resize_lock(struct pglist_data *pgdat) { - spin_lock_irqsave(&pgdat->node_size_lock, *flags); + spin_lock(&pgdat->node_size_lock); } static inline -void pgdat_resize_unlock(struct pglist_data *pgdat, unsigned long *flags) +void pgdat_resize_unlock(struct pglist_data *pgdat) { - spin_unlock_irqrestore(&pgdat->node_size_lock, *flags); + spin_unlock(&pgdat->node_size_lock); } static inline void pgdat_resize_init(struct pglist_data *pgdat) >> >From my understanding, we don't access pgdat from interrupt context. >> >> BTW, one more confirmation. One irqsave lock means we can't do something >> during holding the lock, like sleep. Is my understanding correct? > >You cannot sleep in any atomic context. IRQ safe lock only means that >IRQs are disabled along with the lock. The irqsave variant should be >taken when an IRQ context itself can take the lock. There is a lot of >documentation to clarify this e.g. Linux Device Drivers. I would >recommend to read through that. > Thanks. I took a look at this one which seems to resolve my confusion. https://www.kernel.org/doc/Documentation/locking/spinlocks.txt >-- >Michal Hocko >SUSE Labs -- Wei Yang Help you, Help me