From: Dan Williams <dan.j.williams@xxxxxxxxx> 3.12-stable review patch. If anyone has any objections, please let me know. =============== commit ac34f15e0c6d2fd58480052b6985f6991fb53bcc upstream. When tearing down a block device early in its lifetime, userspace may still be performing discovery actions like blkdev_ioctl() to re-read partitions. The nvdimm_revalidate_disk() implementation depends on disk->driverfs_dev to be valid at entry. However, it is set to NULL in del_gendisk() and fatally this is happening *before* the disk device is deleted from userspace view. There's no reason for del_gendisk() to clear ->driverfs_dev. That device is the parent of the disk. It is guaranteed to not be freed until the disk, as a child, drops its ->parent reference. We could also fix this issue locally in nvdimm_revalidate_disk() by using disk_to_dev(disk)->parent, but lets fix it globally since ->driverfs_dev follows the lifetime of the parent. Longer term we should probably just add a @parent parameter to add_disk(), and stop carrying this pointer in the gendisk. BUG: unable to handle kernel NULL pointer dereference at (null) IP: [<ffffffffa00340a8>] nvdimm_revalidate_disk+0x18/0x90 [libnvdimm] CPU: 2 PID: 538 Comm: systemd-udevd Tainted: G O 4.4.0-rc5 #2257 [..] Call Trace: [<ffffffff8143e5c7>] rescan_partitions+0x87/0x2c0 [<ffffffff810f37f9>] ? __lock_is_held+0x49/0x70 [<ffffffff81438c62>] __blkdev_reread_part+0x72/0xb0 [<ffffffff81438cc5>] blkdev_reread_part+0x25/0x40 [<ffffffff8143982d>] blkdev_ioctl+0x4fd/0x9c0 [<ffffffff811246c9>] ? current_kernel_time64+0x69/0xd0 [<ffffffff812916dd>] block_ioctl+0x3d/0x50 [<ffffffff81264c38>] do_vfs_ioctl+0x308/0x560 [<ffffffff8115dbd1>] ? __audit_syscall_entry+0xb1/0x100 [<ffffffff810031d6>] ? do_audit_syscall_entry+0x66/0x70 [<ffffffff81264f09>] SyS_ioctl+0x79/0x90 [<ffffffff81902672>] entry_SYSCALL_64_fastpath+0x12/0x76 Cc: Jan Kara <jack@xxxxxxx> Cc: Jens Axboe <axboe@xxxxxx> Reported-by: Robert Hu <robert.hu@xxxxxxxxx> Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx> Signed-off-by: Jiri Slaby <jslaby@xxxxxxx> --- block/genhd.c | 1 - 1 file changed, 1 deletion(-) diff --git a/block/genhd.c b/block/genhd.c index 38d4ba122a43..037cf3e8f1bd 100644 --- a/block/genhd.c +++ b/block/genhd.c @@ -662,7 +662,6 @@ void del_gendisk(struct gendisk *disk) kobject_put(disk->part0.holder_dir); kobject_put(disk->slave_dir); - disk->driverfs_dev = NULL; if (!sysfs_deprecated) sysfs_remove_link(block_depr, dev_name(disk_to_dev(disk))); pm_runtime_set_memalloc_noio(disk_to_dev(disk), false); -- 2.12.2