From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754561AbcKUNsK (ORCPT ); Mon, 21 Nov 2016 08:48:10 -0500 Received: from mx2.suse.de ([195.135.220.15]:60200 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753261AbcKUNsI (ORCPT ); Mon, 21 Nov 2016 08:48:08 -0500 Date: Mon, 21 Nov 2016 14:48:06 +0100 Message-ID: From: Takashi Iwai To: Minchan Kim , Nitin Gupta Cc: Sergey Senozhatsky , David Disseldorp , linux-kernel@vger.kernel.org Subject: Re: [PATCH] zram: Fix unbalanced idr management at hot removal In-Reply-To: <20161121132140.12683-1-tiwai@suse.de> References: <20161121132140.12683-1-tiwai@suse.de> User-Agent: Wanderlust/2.15.9 (Almost Unreal) SEMI/1.14.6 (Maruoka) FLIM/1.14.9 (=?UTF-8?B?R29qxY0=?=) APEL/10.8 Emacs/24.5 (x86_64-suse-linux-gnu) MULE/6.0 (HANACHIRUSATO) MIME-Version: 1.0 (generated by SEMI 1.14.6 - "Maruoka") Content-Type: text/plain; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 21 Nov 2016 14:21:40 +0100, Takashi Iwai wrote: > > The zram hot removal code calls idr_remove() even when zram_remove() > returns an error (typically -EBUSY). This results in a leftover at > the device release, eventually leading to a crash when the module is > reloaded. > > As described in the bug report below, the following procedure would > cause an Oops with zram: > > - provision three zram devices via modprobe zram num_devices=3 > - configure a size for each device > + echo "1G" > /sys/block/$zram_name/disksize > - mkfs and mount zram0 only > - attempt to hot remove all three devices > + echo 2 > /sys/class/zram-control/hot_remove > + echo 1 > /sys/class/zram-control/hot_remove > + echo 0 > /sys/class/zram-control/hot_remove > - zram0 removal fails with EBUSY, as expected > - unmount zram0 > - try zram0 hot remove again > + echo 0 > /sys/class/zram-control/hot_remove > - fails with ENODEV (unexpected) > - unload zram kernel module > + completes successfully > - zram0 device node still exists > - attempt to mount /dev/zram0 > + mount command is killed > + following BUG is encountered > > BUG: unable to handle kernel paging request at ffffffffa0002ba0 > IP: [] get_disk+0x16/0x50 > Oops: 0000 [#1] SMP > CPU: 0 PID: 252 Comm: mount Not tainted 4.9.0-rc6 #176 > task: ffff88001a9f2800 task.stack: ffffc90000300000 > RIP: 0010:[] [] get_disk+0x16/0x50 > Call Trace: > [] exact_lock+0xc/0x20 > [] kobj_lookup+0xdc/0x160 > [] ? disk_map_sector_rcu+0x70/0x70 > [] ? blkdev_get_by_dev+0x50/0x50 > [] get_gendisk+0x2f/0x110 > [] ? blkdev_get_by_dev+0x50/0x50 > [] __blkdev_get+0x10c/0x3c0 > [] ? blkdev_get_by_dev+0x50/0x50 > [] blkdev_get+0x19d/0x2e0 > [] ? blkdev_get_by_dev+0x50/0x50 > [] blkdev_open+0x56/0x70 > [] do_dentry_open.isra.19+0x1ff/0x310 > [] vfs_open+0x43/0x60 > [] path_openat+0x2c9/0xf30 > [] ? __save_stack_trace+0x40/0xd0 > [] do_filp_open+0x79/0xd0 > [] ? kmemleak_alloc+0x49/0xa0 > [] do_sys_open+0x114/0x1e0 > [] SyS_open+0x19/0x20 > [] entry_SYSCALL_64_fastpath+0x13/0x94 > > This patch adds the proper error check in hot_remove_store() not to > call idr_remove() unconditionally. > > Bugzilla: https://bugzilla.opensuse.org/show_bug.cgi?id=1010970 > Reported-and-tested-by: David Disseldorp > Reviewed-by: David Disseldorp > Cc: > Signed-off-by: Takashi Iwai Forgot to add Fixes tag: Fixes: 17ec4cd98578 ("zram: don't call idr_remove() from zram_remove()") Takashi > --- > drivers/block/zram/zram_drv.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c > index 04365b17ee67..5163c8f918cb 100644 > --- a/drivers/block/zram/zram_drv.c > +++ b/drivers/block/zram/zram_drv.c > @@ -1403,7 +1403,8 @@ static ssize_t hot_remove_store(struct class *class, > zram = idr_find(&zram_index_idr, dev_id); > if (zram) { > ret = zram_remove(zram); > - idr_remove(&zram_index_idr, dev_id); > + if (!ret) > + idr_remove(&zram_index_idr, dev_id); > } else { > ret = -ENODEV; > } > -- > 2.10.2 >