Commit be35f486 authored by Mikulas Patocka's avatar Mikulas Patocka Committed by Mike Snitzer
Browse files

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

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: default avatarMikulas Patocka <mpatocka@redhat.com>
Signed-off-by: default avatarMike Snitzer <snitzer@redhat.com>
Cc: stable@vger.kernel.org
parent 1ddd641d

drivers/md/dm-sysfs.c

+9 −1
Original line number Diff line number Diff line
@@ -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));

}

drivers/md/dm.c

+11 −0
Original line number Diff line number Diff line
@@ -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);

drivers/md/dm.h

+2 −0
Original line number Diff line number Diff line
@@ -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

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