From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f69.google.com (mail-wm0-f69.google.com [74.125.82.69]) by kanga.kvack.org (Postfix) with ESMTP id 35DE56B0010 for ; Tue, 17 Jul 2018 11:56:37 -0400 (EDT) Received: by mail-wm0-f69.google.com with SMTP id s18-v6so672369wmh.0 for ; Tue, 17 Jul 2018 08:56:37 -0700 (PDT) Received: from Galois.linutronix.de (Galois.linutronix.de. [2a01:7a0:2:106d:700::1]) by mx.google.com with ESMTPS id u9-v6si1102539wmu.213.2018.07.17.08.56.35 for (version=TLS1_2 cipher=AES128-SHA bits=128/128); Tue, 17 Jul 2018 08:56:35 -0700 (PDT) Date: Tue, 17 Jul 2018 17:56:30 +0200 From: Sebastian Andrzej Siewior Subject: Re: [PATCH 3/6] bdi: Use refcount_t for reference counting instead atomic_t Message-ID: <20180717155630.5propcebpubol6x3@linutronix.de> References: <20180703200141.28415-1-bigeasy@linutronix.de> <20180703200141.28415-4-bigeasy@linutronix.de> <20180716155716.1f7ac43d211133a8cb476637@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20180716155716.1f7ac43d211133a8cb476637@linux-foundation.org> Sender: owner-linux-mm@kvack.org List-ID: To: Andrew Morton Cc: linux-kernel@vger.kernel.org, tglx@linutronix.de, Peter Zijlstra , Ingo Molnar , linux-mm@kvack.org, Jens Axboe On 2018-07-16 15:57:16 [-0700], Andrew Morton wrote: > > --- a/mm/backing-dev.c > > +++ b/mm/backing-dev.c > > @@ -438,10 +438,10 @@ wb_congested_get_create(struct backing_dev_info *bdi, int blkcg_id, gfp_t gfp) > > if (new_congested) { > > /* !found and storage for new one already allocated, insert */ > > congested = new_congested; > > - new_congested = NULL; > > rb_link_node(&congested->rb_node, parent, node); > > rb_insert_color(&congested->rb_node, &bdi->cgwb_congested_tree); > > - goto found; > > + spin_unlock_irqrestore(&cgwb_lock, flags); > > + return congested; > > } > > > > spin_unlock_irqrestore(&cgwb_lock, flags); > > @@ -451,13 +451,13 @@ wb_congested_get_create(struct backing_dev_info *bdi, int blkcg_id, gfp_t gfp) > > if (!new_congested) > > return NULL; > > > > - atomic_set(&new_congested->refcnt, 0); > > + refcount_set(&new_congested->refcnt, 1); > > new_congested->__bdi = bdi; > > new_congested->blkcg_id = blkcg_id; > > goto retry; > > > > found: > > - atomic_inc(&congested->refcnt); > > + refcount_inc(&congested->refcnt); > > spin_unlock_irqrestore(&cgwb_lock, flags); > > kfree(new_congested); > > return congested; > > > > ... > > > > I'm not sure that the restructuring of wb_congested_get_create() was > desirable and it does make the patch harder to review. But it looks > OK to me. By `restructuring' you mean the addition of return statement instead using the goto label in the first hunk? If so, then you would have refcount_set(&new_congested->refcnt, 0); refcount_inc(&congested->refcnt); which is a 0 -> 1 transition and is forbidden by refcount_t. So I had to avoid this one. Thank you applying the patches! You applied the bdi and userns switch from atomic_t to refcount_t. There were also the patches [PATCH 4/6] bdi: Use irqsave variant of refcount_dec_and_lock() [PATCH 6/6] userns: Use irqsave variant of refcount_dec_and_lock() in the series which make use the irqsave version of refcount_dec_and_lock(). Did you miss them by chance or skipped them on purpose? Sebastian