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[67.188.94.199]) by smtp.gmail.com with ESMTPSA id s10sm3915048pjn.35.2020.11.25.17.11.08 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 25 Nov 2020 17:11:10 -0800 (PST) Date: Wed, 25 Nov 2020 17:11:07 -0800 From: Minchan Kim To: Christoph Hellwig Message-ID: <20201126011107.GA57352@google.com> References: <20201116145809.410558-1-hch@lst.de> <20201116145809.410558-61-hch@lst.de> MIME-Version: 1.0 In-Reply-To: <20201116145809.410558-61-hch@lst.de> X-Mimecast-Impersonation-Protect: Policy=CLT - Impersonation Protection Definition; Similar Internal Domain=false; Similar Monitored External Domain=false; Custom External Domain=false; Mimecast External Domain=false; Newly Observed Domain=false; Internal User Name=false; Custom Display Name List=false; Reply-to Address Mismatch=false; Targeted Threat Dictionary=false; Mimecast Threat Dictionary=false; Custom Threat Dictionary=false X-Mimecast-Bulk-Signature: yes X-Mimecast-Spam-Signature: bulk X-Scanned-By: MIMEDefang 2.79 on 10.11.54.5 X-loop: dm-devel@redhat.com X-Mailman-Approved-At: Thu, 26 Nov 2020 03:35:50 -0500 Cc: Justin Sanders , Mike Snitzer , "Michael S. Tsirkin" , Jason Wang , linux-nvme@lists.infradead.org, Song Liu , dm-devel@redhat.com, linux-scsi@vger.kernel.org, xen-devel@lists.xenproject.org, Ilya Dryomov , Jack Wang , Konrad Rzeszutek Wilk , Josef Bacik , nbd@other.debian.org, linux-raid@vger.kernel.org, Stefan Hajnoczi , drbd-dev@tron.linbit.com, ceph-devel@vger.kernel.org, Jens Axboe , linux-block@vger.kernel.org, "Martin K. Petersen" , Sergey Senozhatsky , linux-fsdevel@vger.kernel.org, Paolo Bonzini , Roger Pau =?iso-8859-1?Q?Monn=E9?= Subject: Re: [dm-devel] [PATCH 60/78] zram: remove the claim mechanism X-BeenThere: dm-devel@redhat.com X-Mailman-Version: 2.1.12 Precedence: junk List-Id: device-mapper development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: dm-devel-bounces@redhat.com Errors-To: dm-devel-bounces@redhat.com X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=dm-devel-bounces@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Disposition: inline Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit On Mon, Nov 16, 2020 at 03:57:51PM +0100, Christoph Hellwig wrote: > The zram claim mechanism was added to ensure no new opens come in > during teardown. But the proper way to archive that is to call > del_gendisk first, which takes care of all that. Once del_gendisk > is called in the right place, the reset side can also be simplified > as no I/O can be outstanding on a block device that is not open. It would be great if it makes the mess simple. Let me have a question Please see below. > > Signed-off-by: Christoph Hellwig > --- > drivers/block/zram/zram_drv.c | 76 ++++++++++------------------------- > 1 file changed, 21 insertions(+), 55 deletions(-) > > diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c > index 6d15d51cee2b7e..3641434a9b154d 100644 > --- a/drivers/block/zram/zram_drv.c > +++ b/drivers/block/zram/zram_drv.c > @@ -1756,64 +1756,33 @@ static ssize_t disksize_store(struct device *dev, > static ssize_t reset_store(struct device *dev, > struct device_attribute *attr, const char *buf, size_t len) > { > - int ret; > - unsigned short do_reset; > - struct zram *zram; > + struct zram *zram = dev_to_zram(dev); > struct block_device *bdev; > + unsigned short do_reset; > + int ret = 0; > > ret = kstrtou16(buf, 10, &do_reset); > if (ret) > return ret; > - > if (!do_reset) > return -EINVAL; > > - zram = dev_to_zram(dev); > bdev = bdget_disk(zram->disk, 0); > if (!bdev) > return -ENOMEM; > > mutex_lock(&bdev->bd_mutex); > - /* Do not reset an active device or claimed device */ > - if (bdev->bd_openers || zram->claim) { > - mutex_unlock(&bdev->bd_mutex); > - bdput(bdev); > - return -EBUSY; > - } > - > - /* From now on, anyone can't open /dev/zram[0-9] */ > - zram->claim = true; > + if (bdev->bd_openers) > + ret = -EBUSY; > + else > + zram_reset_device(zram); > mutex_unlock(&bdev->bd_mutex); > - > - /* Make sure all the pending I/O are finished */ > - fsync_bdev(bdev); > - zram_reset_device(zram); > bdput(bdev); > > - mutex_lock(&bdev->bd_mutex); > - zram->claim = false; > - mutex_unlock(&bdev->bd_mutex); > - > - return len; > -} > - > -static int zram_open(struct block_device *bdev, fmode_t mode) > -{ > - int ret = 0; > - struct zram *zram; > - > - WARN_ON(!mutex_is_locked(&bdev->bd_mutex)); > - > - zram = bdev->bd_disk->private_data; > - /* zram was claimed to reset so open request fails */ > - if (zram->claim) > - ret = -EBUSY; > - > - return ret; > + return ret ? ret : len; > } > > static const struct block_device_operations zram_devops = { > - .open = zram_open, > .submit_bio = zram_submit_bio, > .swap_slot_free_notify = zram_slot_free_notify, > .rw_page = zram_rw_page, > @@ -1821,7 +1790,6 @@ static const struct block_device_operations zram_devops = { > }; > > static const struct block_device_operations zram_wb_devops = { > - .open = zram_open, > .submit_bio = zram_submit_bio, > .swap_slot_free_notify = zram_slot_free_notify, > .owner = THIS_MODULE > @@ -1972,34 +1940,32 @@ static int zram_add(void) > return ret; > } > > -static int zram_remove(struct zram *zram) > +static bool zram_busy(struct zram *zram) > { > struct block_device *bdev; > + bool busy = false; > > bdev = bdget_disk(zram->disk, 0); > - if (!bdev) > - return -ENOMEM; > - > - mutex_lock(&bdev->bd_mutex); > - if (bdev->bd_openers || zram->claim) { > - mutex_unlock(&bdev->bd_mutex); > + if (bdev) { > + if (bdev->bd_openers) > + busy = true; > bdput(bdev); > - return -EBUSY; > } > > - zram->claim = true; > - mutex_unlock(&bdev->bd_mutex); > + return busy; > +} > > - zram_debugfs_unregister(zram); > +static int zram_remove(struct zram *zram) > +{ > + if (zram_busy(zram)) > + return -EBUSY; > > - /* Make sure all the pending I/O are finished */ > - fsync_bdev(bdev); > + del_gendisk(zram->disk); > + zram_debugfs_unregister(zram); > zram_reset_device(zram); > - bdput(bdev); > > pr_info("Removed device: %s\n", zram->disk->disk_name); > > - del_gendisk(zram->disk); > blk_cleanup_queue(zram->disk->queue); > put_disk(zram->disk); > kfree(zram); > -- > 2.29.2 > With this patch, how deal with the race? CPU 1 CPU 2 hot_remove_store zram_remove zram_busy return -EBUSY open /dev/zram0 del_gendisk zram_reset and destroy -- dm-devel mailing list dm-devel@redhat.com https://www.redhat.com/mailman/listinfo/dm-devel