From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752858AbaCAAcJ (ORCPT ); Fri, 28 Feb 2014 19:32:09 -0500 Received: from mail.linuxfoundation.org ([140.211.169.12]:52891 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752389AbaCAAcH (ORCPT ); Fri, 28 Feb 2014 19:32:07 -0500 Date: Fri, 28 Feb 2014 16:32:06 -0800 From: Andrew Morton To: Minchan Kim Cc: Sasha Levin , ngupta@vflare.org, LKML , Sergey Senozhatsky Subject: Re: zram: lockdep spew for zram->init_lock Message-Id: <20140228163206.f772a6f4ceb876f2f9a58031@linux-foundation.org> In-Reply-To: <20140227235629.GF31407@bbox> References: <530F5045.1010604@oracle.com> <20140227235629.GF31407@bbox> X-Mailer: Sylpheed 3.2.0beta5 (GTK+ 2.24.10; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 28 Feb 2014 08:56:29 +0900 Minchan Kim wrote: > Sasha reported following below lockdep spew of zram. > > It was introduced by [1] in recent linux-next but it's false positive > because zram_meta_alloc with down_write(init_lock) couldn't be called > during zram is working as swap device so we could annotate the lock. > > But I don't think it's worthy because it would make greate lockdep > less effective. Instead, move zram_meta_alloc out of the lock as good > old day so we could do unnecessary allocation/free of zram_meta for > initialied device as Sergey claimed in [1] but it wouldn't be common > and be harmful if someone might do it. Rather than, I'd like to respect > lockdep which is great tool to prevent upcoming subtle bugs. > > [1] zram: delete zram_init_device > > ... > > --- a/drivers/block/zram/zram_drv.c > +++ b/drivers/block/zram/zram_drv.c > @@ -537,26 +537,27 @@ static ssize_t disksize_store(struct device *dev, > struct device_attribute *attr, const char *buf, size_t len) > { > u64 disksize; > + struct zram_meta *meta; > struct zram *zram = dev_to_zram(dev); > > disksize = memparse(buf, NULL); > if (!disksize) > return -EINVAL; > > + disksize = PAGE_ALIGN(disksize); > + meta = zram_meta_alloc(disksize); > + if (!meta) > + return -ENOMEM; > + > down_write(&zram->init_lock); > if (init_done(zram)) { > + zram_meta_free(meta); > up_write(&zram->init_lock); > pr_info("Cannot change disksize for initialized device\n"); > return -EBUSY; > } > > - disksize = PAGE_ALIGN(disksize); > - zram->meta = zram_meta_alloc(disksize); > - if (!zram->meta) { > - up_write(&zram->init_lock); > - return -ENOMEM; > - } > - > + zram->meta = meta; > zram->disksize = disksize; > set_capacity(zram->disk, zram->disksize >> SECTOR_SHIFT); > up_write(&zram->init_lock); When applying zram-use-zcomp-compressing-backends.patch on top of this we get a bit of a mess, and simple conflict resolution results in a leak. disksize_store() was one of those nasty functions which does multiple "return" statements after performing locking and resource allocation. As usual, this led to a resource leak. Remember folks, "return" is a goto in disguise. Here's what I ended up with. Please review. static ssize_t disksize_store(struct device *dev, struct device_attribute *attr, const char *buf, size_t len) { u64 disksize; struct zram_meta *meta; struct zram *zram = dev_to_zram(dev); int err; disksize = memparse(buf, NULL); if (!disksize) return -EINVAL; disksize = PAGE_ALIGN(disksize); meta = zram_meta_alloc(disksize); if (!meta) return -ENOMEM; down_write(&zram->init_lock); if (init_done(zram)) { pr_info("Cannot change disksize for initialized device\n"); err = -EBUSY; goto out_free_meta; } zram->comp = zcomp_create(default_compressor); if (!zram->comp) { pr_info("Cannot initialise %s compressing backend\n", default_compressor); err = -EINVAL; goto out_free_meta; } zram->meta = meta; zram->disksize = disksize; set_capacity(zram->disk, zram->disksize >> SECTOR_SHIFT); up_write(&zram->init_lock); return len; out_free_meta: up_write(&zram->init_lock); zram_meta_free(meta); return err; }