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dm: wait until embedded kobject is released before destroying a device

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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>
Cc: stable@vger.kernel.org
This commit is contained in:
Mikulas Patocka 2014-01-06 23:01:22 -05:00 committed by Mike Snitzer
parent 1ddd641ddc
commit be35f48610
3 changed files with 22 additions and 1 deletions
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10
drivers/md/dm-sysfs.c
View File

@ -79,6 +79,11 @@ static const struct sysfs_ops dm_sysfs_ops = {
.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 const struct sysfs_ops dm_sysfs_ops = {
static struct kobj_type dm_ktype = {
.sysfs_ops = &dm_sysfs_ops,
.default_attrs = dm_attrs,
.release = dm_kobject_release,
};
/*
@ -104,5 +110,7 @@ int dm_sysfs_init(struct mapped_device *md)
*/
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));
}

11
drivers/md/dm.c
View File

@ -203,6 +203,9 @@ struct mapped_device {
/* sysfs handle */
struct kobject kobj;
/* wait until the kobject is released */
struct completion kobj_completion;
/* zero-length flush that will be cloned and submitted to targets */
struct bio flush_bio;
@ -2041,6 +2044,7 @@ static struct mapped_device *alloc_dev(int minor)
init_waitqueue_head(&md->wait);
INIT_WORK(&md->work, dm_wq_work);
init_waitqueue_head(&md->eventq);
init_completion(&md->kobj_completion);
md->disk->major = _major;
md->disk->first_minor = minor;
@ -2919,6 +2923,13 @@ struct mapped_device *dm_get_from_kobject(struct kobject *kobj)
return md;
}
struct completion *dm_get_completion_from_kobject(struct kobject *kobj)
{
struct mapped_device *md = container_of(kobj, struct mapped_device, kobj);
return &md->kobj_completion;
}
int dm_suspended_md(struct mapped_device *md)
{
return test_bit(DMF_SUSPENDED, &md->flags);

2
drivers/md/dm.h
View File

@ -15,6 +15,7 @@
#include <linux/list.h>
#include <linux/blkdev.h>
#include <linux/hdreg.h>
#include <linux/completion.h>
#include "dm-stats.h"
@ -152,6 +153,7 @@ int dm_sysfs_init(struct mapped_device *md);
void dm_sysfs_exit(struct mapped_device *md);
struct kobject *dm_kobject(struct mapped_device *md);
struct mapped_device *dm_get_from_kobject(struct kobject *kobj);
struct completion *dm_get_completion_from_kobject(struct kobject *kobj);
/*
* Targets for linear and striped mappings