This is a note to let you know that I've just added the patch titled btrfs: fix put of uninitialized kobject after seed device delete to the 5.8-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: btrfs-fix-put-of-uninitialized-kobject-after-seed-device-delete.patch and it can be found in the queue-5.8 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From b5ddcffa37778244d5e786fe32f778edf2bfc93e Mon Sep 17 00:00:00 2001 From: Anand Jain <anand.jain@xxxxxxxxxx> Date: Sat, 5 Sep 2020 01:34:21 +0800 Subject: btrfs: fix put of uninitialized kobject after seed device delete From: Anand Jain <anand.jain@xxxxxxxxxx> commit b5ddcffa37778244d5e786fe32f778edf2bfc93e upstream. The following test case leads to NULL kobject free error: mount seed /mnt add sprout to /mnt umount /mnt mount sprout to /mnt delete seed kobject: '(null)' (00000000dd2b87e4): is not initialized, yet kobject_put() is being called. WARNING: CPU: 1 PID: 15784 at lib/kobject.c:736 kobject_put+0x80/0x350 RIP: 0010:kobject_put+0x80/0x350 :: Call Trace: btrfs_sysfs_remove_devices_dir+0x6e/0x160 [btrfs] btrfs_rm_device.cold+0xa8/0x298 [btrfs] btrfs_ioctl+0x206c/0x22a0 [btrfs] ksys_ioctl+0xe2/0x140 __x64_sys_ioctl+0x1e/0x29 do_syscall_64+0x96/0x150 entry_SYSCALL_64_after_hwframe+0x44/0xa9 RIP: 0033:0x7f4047c6288b :: This is because, at the end of the seed device-delete, we try to remove the seed's devid sysfs entry. But for the seed devices under the sprout fs, we don't initialize the devid kobject yet. So add a kobject state check, which takes care of the bug. Fixes: 668e48af7a94 ("btrfs: sysfs, add devid/dev_state kobject and device attributes") CC: stable@xxxxxxxxxxxxxxx # 5.6+ Signed-off-by: Anand Jain <anand.jain@xxxxxxxxxx> Reviewed-by: David Sterba <dsterba@xxxxxxxx> Signed-off-by: David Sterba <dsterba@xxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- fs/btrfs/sysfs.c | 16 ++++++++++------ 1 file changed, 10 insertions(+), 6 deletions(-) --- a/fs/btrfs/sysfs.c +++ b/fs/btrfs/sysfs.c @@ -1165,10 +1165,12 @@ int btrfs_sysfs_remove_devices_dir(struc disk_kobj->name); } - kobject_del(&one_device->devid_kobj); - kobject_put(&one_device->devid_kobj); + if (one_device->devid_kobj.state_initialized) { + kobject_del(&one_device->devid_kobj); + kobject_put(&one_device->devid_kobj); - wait_for_completion(&one_device->kobj_unregister); + wait_for_completion(&one_device->kobj_unregister); + } return 0; } @@ -1181,10 +1183,12 @@ int btrfs_sysfs_remove_devices_dir(struc sysfs_remove_link(fs_devices->devices_kobj, disk_kobj->name); } - kobject_del(&one_device->devid_kobj); - kobject_put(&one_device->devid_kobj); + if (one_device->devid_kobj.state_initialized) { + kobject_del(&one_device->devid_kobj); + kobject_put(&one_device->devid_kobj); - wait_for_completion(&one_device->kobj_unregister); + wait_for_completion(&one_device->kobj_unregister); + } } return 0; Patches currently in stable-queue which might be from anand.jain@xxxxxxxxxx are queue-5.8/btrfs-fix-put-of-uninitialized-kobject-after-seed-device-delete.patch