dm: wait until embedded kobject is released before destroying a device
commit be35f486108227e10fe5d96fd42fb2b344c59983 upstream.
There may be other parts of the kernel holding a reference on the dm
kobject. We must wait until all references are dropped before
deallocating the mapped_device structure.
The dm_kobject_release method signals that all references are dropped
via completion. But dm_kobject_release doesn't free the kobject (which
is embedded in the mapped_device structure).
This is the sequence of operations:
* when destroying a DM device, call kobject_put from dm_sysfs_exit
* wait until all users stop using the kobject, when it happens the
release method is called
* the release method signals the completion and should return without
delay
* the dm device removal code that waits on the completion continues
* the dm device removal code drops the dm_mod reference the device had
* the dm device removal code frees the mapped_device structure that
contains the kobject
Using kobject this way should avoid the module unload race that was
mentioned at the beginning of this thread:
https://lkml.org/lkml/2014/1/4/83
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
diff --git a/drivers/md/dm-sysfs.c b/drivers/md/dm-sysfs.c
index 84d2b91..e0cc5d6 100644
--- a/drivers/md/dm-sysfs.c
+++ b/drivers/md/dm-sysfs.c
@@ -79,6 +79,11 @@
.show = dm_attr_show,
};
+static void dm_kobject_release(struct kobject *kobj)
+{
+ complete(dm_get_completion_from_kobject(kobj));
+}
+
/*
* dm kobject is embedded in mapped_device structure
* no need to define release function here
@@ -86,6 +91,7 @@
static struct kobj_type dm_ktype = {
.sysfs_ops = &dm_sysfs_ops,
.default_attrs = dm_attrs,
+ .release = dm_kobject_release,
};
/*
@@ -104,5 +110,7 @@
*/
void dm_sysfs_exit(struct mapped_device *md)
{
- kobject_put(dm_kobject(md));
+ struct kobject *kobj = dm_kobject(md);
+ kobject_put(kobj);
+ wait_for_completion(dm_get_completion_from_kobject(kobj));
}