From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pa0-f48.google.com (mail-pa0-f48.google.com [209.85.220.48]) by kanga.kvack.org (Postfix) with ESMTP id 3A0F46B0259 for ; Tue, 15 Dec 2015 18:41:11 -0500 (EST) Received: by mail-pa0-f48.google.com with SMTP id ur14so13150562pab.0 for ; Tue, 15 Dec 2015 15:41:11 -0800 (PST) Received: from mail.linuxfoundation.org (mail.linuxfoundation.org. [140.211.169.12]) by mx.google.com with ESMTPS id p18si780249pfi.243.2015.12.15.15.41.10 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 15 Dec 2015 15:41:10 -0800 (PST) Date: Tue, 15 Dec 2015 15:41:09 -0800 From: Andrew Morton Subject: Re: [-mm PATCH v2 19/25] list: introduce list_del_poison() Message-Id: <20151215154109.54f3cb025944ac7166bf6f64@linux-foundation.org> In-Reply-To: <20151210023855.30368.37457.stgit@dwillia2-desk3.jf.intel.com> References: <20151210023708.30368.92962.stgit@dwillia2-desk3.jf.intel.com> <20151210023855.30368.37457.stgit@dwillia2-desk3.jf.intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Dan Williams Cc: linux-mm@kvack.org, linux-nvdimm@ml01.01.org On Wed, 09 Dec 2015 18:38:55 -0800 Dan Williams wrote: > ZONE_DEVICE pages always have an elevated count and will never be on an > lru reclaim list. That space in 'struct page' can be redirected for > other uses, but for safety introduce a poison value that will always > trip __list_add() to assert. This allows half of the struct list_head > storage to be reclaimed with some assurance to back up the assumption > that the page count never goes to zero and a list_add() is never > attempted. > > ... > > --- a/include/linux/list.h > +++ b/include/linux/list.h > @@ -108,9 +108,26 @@ static inline void list_del(struct list_head *entry) > entry->next = LIST_POISON1; > entry->prev = LIST_POISON2; > } > + > +#define list_del_poison list_del > #else > extern void __list_del_entry(struct list_head *entry); > extern void list_del(struct list_head *entry); > +extern struct list_head list_force_poison; > + > +/** > + * list_del_poison - poison an entry to always assert on list_add > + * @entry: the element to delete and poison > + * > + * Note: the assertion on list_add() only occurs when CONFIG_DEBUG_LIST=y, > + * otherwise this is identical to list_del() > + */ > +static inline void list_del_poison(struct list_head *entry) > +{ > + __list_del(entry->prev, entry->next); > + entry->next = &list_force_poison; > + entry->prev = &list_force_poison; > +} > #endif list_del() already poisons the list_head. Does this really add anything? > /** > diff --git a/lib/list_debug.c b/lib/list_debug.c > index 3859bf63561c..d730c064a4df 100644 > --- a/lib/list_debug.c > +++ b/lib/list_debug.c > @@ -12,6 +12,8 @@ > #include > #include > > +struct list_head list_force_poison; > + > /* > * Insert a new entry between two known consecutive entries. > * > @@ -23,6 +25,8 @@ void __list_add(struct list_head *new, > struct list_head *prev, > struct list_head *next) > { > + WARN(new->next == &list_force_poison || new->prev == &list_force_poison, > + "list_add attempted on force-poisoned entry\n"); I suppose that list_replace() should poison as well, and perhaps other places were missed. -- 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