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
Call Trace:
exact_lock+0xc/0x20
kobj_lookup+0xdc/0x160
get_gendisk+0x2f/0x110
__blkdev_get+0x10c/0x3c0
blkdev_get+0x19d/0x2e0
blkdev_open+0x56/0x70
do_dentry_open.isra.19+0x1ff/0x310
vfs_open+0x43/0x60
path_openat+0x2c9/0xf30
do_filp_open+0x79/0xd0
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.
Fixes: 17ec4cd985 ("zram: don't call idr_remove() from zram_remove()")
Bugzilla: https://bugzilla.opensuse.org/show_bug.cgi?id=1010970
Link: http://lkml.kernel.org/r/20161121132140.12683-1-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Reviewed-by: David Disseldorp <ddiss@suse.de>
Reported-by: David Disseldorp <ddiss@suse.de>
Tested-by: David Disseldorp <ddiss@suse.de>
Acked-by: Minchan Kim <minchan@kernel.org>
Acked-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: <stable@vger.kernel.org> [4.4+]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
529e71e164