Hi,
在 2025/8/7 19:47, Nilay Shroff 写道:
On 8/7/25 12:50 PM, Zheng Qixing wrote:
From: Zheng Qixing <zhengqixing@xxxxxxxxxx>
Device-mapper can call add_disk() multiple times for the same gendisk
due to its two-phase creation process (dm create + dm load). This leads
to kobject double initialization errors when the underlying iSCSI devices
become temporarily unavailable and then reappear.
However, if the first add_disk() call fails and is retried, the queue_kobj
gets initialized twice, causing:
kobject: kobject (ffff88810c27bb90): tried to init an initialized object,
something is seriously wrong.
Call Trace:
<TASK>
dump_stack_lvl+0x5b/0x80
kobject_init.cold+0x43/0x51
blk_register_queue+0x46/0x280
add_disk_fwnode+0xb5/0x280
dm_setup_md_queue+0x194/0x1c0
table_load+0x297/0x2d0
ctl_ioctl+0x2a2/0x480
dm_ctl_ioctl+0xe/0x20
__x64_sys_ioctl+0xc7/0x110
do_syscall_64+0x72/0x390
entry_SYSCALL_64_after_hwframe+0x76/0x7e
Fix this by separating kobject initialization from sysfs registration:
- Initialize queue_kobj early during gendisk allocation
- add_disk() only adds the already-initialized kobject to sysfs
- del_gendisk() removes from sysfs but doesn't destroy the kobject
- Final cleanup happens when the disk is released
Fixes: 2bd85221a625 ("block: untangle request_queue refcounting from sysfs")
Reported-by: Li Lingfeng <lilingfeng3@xxxxxxxxxx>
Closes: https://lore.kernel.org/all/83591d0b-2467-433c-bce0-5581298eb161@xxxxxxxxxx/
Signed-off-by: Zheng Qixing <zhengqixing@xxxxxxxxxx>
---
block/blk-sysfs.c | 4 +---
block/blk.h | 1 +
block/genhd.c | 2 ++
3 files changed, 4 insertions(+), 3 deletions(-)
diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
index 396cded255ea..37d8654faff9 100644
--- a/block/blk-sysfs.c
+++ b/block/blk-sysfs.c
@@ -847,7 +847,7 @@ static void blk_queue_release(struct kobject *kobj)
/* nothing to do here, all data is associated with the parent gendisk */
}
-static const struct kobj_type blk_queue_ktype = {
+const struct kobj_type blk_queue_ktype = {
.default_groups = blk_queue_attr_groups,
.sysfs_ops = &queue_sysfs_ops,
.release = blk_queue_release,
@@ -875,7 +875,6 @@ int blk_register_queue(struct gendisk *disk)
struct request_queue *q = disk->queue;
int ret;
- kobject_init(&disk->queue_kobj, &blk_queue_ktype);
ret = kobject_add(&disk->queue_kobj, &disk_to_dev(disk)->kobj, "queue");
if (ret < 0)
goto out_put_queue_kobj;
If the kobject_add() fails here, then we jump to the label out_put_queue_kobj,
where we release/put disk->queue_kobj. That would decrement the kref of
disk->queue_kobj and possibly bring it to zero.
Since we remove the kobject_init() into alloc disk, when the
kobject_add() fails here,
it should return without kobject_del/put().
If kobject_add() succeeds but later steps fail, we should call
kobject_del() to rollback.
The current error handling with kobject_put() in blk_register_queue() is
indeed problematic.
Next time, when we call add_disk() again without invoking kobject_init()
(because the initialization is now moved outside add_disk()), the refcount
of disk->queue_kobj — which was previously released — would now go for a
toss. Wouldn't that lead to use-after-free or inconsistent state?
@@ -986,5 +985,4 @@ void blk_unregister_queue(struct gendisk *disk)
elevator_set_none(q);
blk_debugfs_remove(disk);
- kobject_put(&disk->queue_kobj);
}
I'm thinking a case where add_disk() fails after the queue is registered.
In that case, we call blk_unregister_queue() — which would ideally put()
the disk->queue_kobj.
But if we skip that put() in blk_unregister_queue() (and that's what we do
above), and then later retry add_disk(), wouldn’t kobject_add() from
blk_register_queue() complain loudly — since we’re trying to add a kobject
that was already added previously?
blk_unregister_queue() calls kobject_del(), then the sysfs state is
properly cleaned up
and retry should work fine.
Thanks,
--Nilay
Thanks,
Qixing
