This is a note to let you know that I've just added the patch titled
dm: wait until embedded kobject is released before destroying a device
to the 3.10-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
dm-wait-until-embedded-kobject-is-released-before-destroying-a-device.patch
and it can be found in the queue-3.10 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From be35f486108227e10fe5d96fd42fb2b344c59983 Mon Sep 17 00:00:00 2001
From: Mikulas Patocka <mpatocka@xxxxxxxxxx>
Date: Mon, 6 Jan 2014 23:01:22 -0500
Subject: dm: wait until embedded kobject is released before destroying a device
From: Mikulas Patocka <mpatocka@xxxxxxxxxx>
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@xxxxxxxxxx>
Signed-off-by: Mike Snitzer <snitzer@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
drivers/md/dm-sysfs.c | 10 +++++++++-
drivers/md/dm.c | 11 +++++++++++
drivers/md/dm.h | 2 ++
3 files changed, 22 insertions(+), 1 deletion(-)
--- a/drivers/md/dm-sysfs.c
+++ b/drivers/md/dm-sysfs.c
@@ -79,6 +79,11 @@ static const struct sysfs_ops dm_sysfs_o
.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_o
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 *
*/
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));
}
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -187,6 +187,9 @@ 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;
};
@@ -1904,6 +1907,7 @@ static struct mapped_device *alloc_dev(i
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;
@@ -2758,6 +2762,13 @@ struct mapped_device *dm_get_from_kobjec
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);
--- a/drivers/md/dm.h
+++ b/drivers/md/dm.h
@@ -15,6 +15,7 @@
#include <linux/list.h>
#include <linux/blkdev.h>
#include <linux/hdreg.h>
+#include <linux/completion.h>
/*
* Suspend feature flags
@@ -129,6 +130,7 @@ int dm_sysfs_init(struct mapped_device *
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
Patches currently in stable-queue which might be from mpatocka@xxxxxxxxxx are
queue-3.10/dm-wait-until-embedded-kobject-is-released-before-destroying-a-device.patch
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