Hi The bug is real, but the patch is wrong. As Sashiko noted, kobject_init_and_add would see an uninitialized kboject if it were called the second time.
I created this patch for this bug. Mikulas dm-sysfs: fix misbehavior if kobject_init_and_add fails If kobject_init_and_add, we must call kobject_put (see the comment at kobject_init_and_add). Before calling kobject_init_and_add, we must zero the kobject (see https://lwn.net/Articles/52085/). If the first call to dm_sysfs_init failed, it may be called again, and that second call would see an uninitialized kobject. Cc: [email protected] Fixes: 784aae735d9b ("dm: add name and uuid to sysfs") Signed-off-by: Mikulas Patocka <[email protected]> --- drivers/md/dm-sysfs.c | 17 ++++++++++++++--- 1 file changed, 14 insertions(+), 3 deletions(-) Index: linux-2.6/drivers/md/dm-sysfs.c =================================================================== --- linux-2.6.orig/drivers/md/dm-sysfs.c +++ linux-2.6/drivers/md/dm-sysfs.c @@ -128,9 +128,20 @@ static const struct kobj_type dm_ktype = */ int dm_sysfs_init(struct mapped_device *md) { - return kobject_init_and_add(dm_kobject(md), &dm_ktype, - &disk_to_dev(dm_disk(md))->kobj, - "%s", "dm"); + struct kobject *kobj = dm_kobject(md); + int r; + + /* The kobject must be zeroed before calling kobject_init */ + memset(kobj, 0, sizeof(struct kobject)); + r = kobject_init_and_add(kobj, &dm_ktype, + &disk_to_dev(dm_disk(md))->kobj, + "%s", "dm"); + if (unlikely(r)) { + /* Weird semantics - we must call kobject_put on failure */ + dm_sysfs_exit(md); + return r; + } + return 0; } /* On Tue, 3 Nov 2026, Wentao Liang wrote: > dm_sysfs_init() uses kobject_init_and_add(), which requires a matching > put even when adding the object fails. dm_setup_md_queue() currently > unwinds the disk and holder links without releasing this object. Since > md->type is still DM_TYPE_NONE, cleanup_mapped_device() also skips the > sysfs cleanup, leaving the initialized kobject behind. > > Call dm_sysfs_exit() before unwinding a failed sysfs initialization. This > both puts the kobject and waits for its release callback, including when > CONFIG_DEBUG_KOBJECT_RELEASE delays that callback, before the mapped > device can be freed or its queue setup retried. > > Fixes: 784aae735d9b ("dm: add name and uuid to sysfs") > Cc: [email protected] > Assisted-by: DeepSeek-V4.1-Flash and OpenAI Codex > Signed-off-by: Wentao Liang <[email protected]> > --- > drivers/md/dm.c | 4 +++- > 1 file changed, 3 insertions(+), 1 deletion(-) > > diff --git a/drivers/md/dm.c b/drivers/md/dm.c > index 1881d86111fb..08b87fd6f955 100644 > --- a/drivers/md/dm.c > +++ b/drivers/md/dm.c > @@ -2647,8 +2647,10 @@ int dm_setup_md_queue(struct mapped_device *md, struct > dm_table *t) > mutex_unlock(&md->table_devices_lock); > > r = dm_sysfs_init(md); > - if (r) > + if (r) { > + dm_sysfs_exit(md); > goto lock_out_undo_holders; > + } > > md->type = type; > > -- > 2.34.1 >
