[PATCH 0/6 v5] NFSD: Pin to vfsmount for nfsd exports cache

[PATCH 0/6 v5] NFSD: Pin to vfsmount for nfsd exports cache

[Kinglong Mee]

If there are some mount points(not exported for nfs) under pseudo root,
after client's operation of those entry under the root, anyone *can't*
unmount those mount points until export cache expired.

# cat /etc/exports
/nfs/xfs        *(rw,insecure,no_subtree_check,no_root_squash)
/nfs/pnfs       *(rw,insecure,no_subtree_check,no_root_squash)
# ll /nfs/
total 0
drwxr-xr-x. 3 root root 84 Apr 21 22:27 pnfs
drwxr-xr-x. 3 root root 84 Apr 21 22:27 test
drwxr-xr-x. 2 root root  6 Apr 20 22:01 xfs
# mount /dev/sde /nfs/test
# df
Filesystem                      1K-blocks    Used Available Use% Mounted on
......
/dev/sdd                          1038336   32944   1005392   4% /nfs/pnfs
/dev/sdc                         10475520   32928  10442592   1% /nfs/xfs
/dev/sde                           999320    1284    929224   1% /nfs/test
# mount -t nfs 127.0.0.1:/nfs/ /mnt
# ll /mnt/*/
/mnt/pnfs/:
total 0
-rw-r--r--. 1 root root 0 Apr 21 22:23 attr
drwxr-xr-x. 2 root root 6 Apr 21 22:19 tmp

/mnt/xfs/:
total 0
# umount /nfs/test/
umount: /nfs/test/: target is busy
        (In some cases useful info about processes that
         use the device is found by lsof(8) or fuser(1).)

It's caused by exports cache of nfsd holds the reference of
the path (here is /nfs/test/), so, it can't be umounted.

I don't think that's user expect, they want umount /nfs/test/.
Bruce think user can also umount /nfs/pnfs/ and /nfs/xfs.

This patch site lets nfsd exports pinning to vfsmount, 
not using mntget, so user can umount any exports mountpoint now.

v3, 
1. New helpers path_get_pin/path_put_unpin for path pin.
2. Use kzalloc for allocating memory.

v4, Thanks for Al Viro's commets for the logic of fs_pin.
1. add a completion for pin_kill waiting the reference is decreased to zero.
2. add a work_struct for pin_kill decreases the reference indirectly.
3. free svc_export/svc_expkey in pin_kill, not svc_export_put/svc_expkey_put.
4. svc_export_put/svc_expkey_put go though pin_kill logic.

v5, 
let killing fs_pin under a reference of vfsmnt.

Kinglong Mee (6):
  fs_pin: Initialize value for fs_pin explicitly
  fs_pin: Export functions for specific filesystem
  fs_pin: Kill fs_pin under a reference of vfsmnt
  path: New helpers path_get_pin/path_put_unpin for path pin
  sunrpc: New helper cache_force_expire for cache cleanup
  nfsd: Allows user un-mounting filesystem where nfsd exports base on

 fs/fs_pin.c                  |  4 ++
 fs/namei.c                   | 26 ++++++++++++
 fs/namespace.c               | 10 ++++-
 fs/nfsd/export.c             | 96 +++++++++++++++++++++++++++++++++++---------
 fs/nfsd/export.h             | 18 ++++++++-
 include/linux/fs_pin.h       |  6 +++
 include/linux/path.h         |  4 ++
 include/linux/sunrpc/cache.h | 11 +++++
 8 files changed, 154 insertions(+), 21 deletions(-)

-- 2.4.3

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[PATCH 1/6 v5] fs_pin: Initialize value for fs_pin explicitly

[Kinglong Mee]

Without initialized, done in fs_pin at stack space may
contains strange value.

v3, v4, v5,
Adds macro for header file

Signed-off-by: Kinglong Mee <kinglongmee-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
---
 include/linux/fs_pin.h | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/include/linux/fs_pin.h b/include/linux/fs_pin.h
index 3886b3b..0dde7b7 100644
--- a/include/linux/fs_pin.h
+++ b/include/linux/fs_pin.h
@@ -1,3 +1,6 @@
+#ifndef _LINUX_FS_PIN_H
+#define _LINUX_FS_PIN_H
+
 #include <linux/wait.h>
 
 struct fs_pin {
@@ -16,9 +19,12 @@ static inline void init_fs_pin(struct fs_pin *p, void (*kill)(struct fs_pin *))
 	INIT_HLIST_NODE(&p->s_list);
 	INIT_HLIST_NODE(&p->m_list);
 	p->kill = kill;
+	p->done = 0;
 }
 
 void pin_remove(struct fs_pin *);
 void pin_insert_group(struct fs_pin *, struct vfsmount *, struct hlist_head *);
 void pin_insert(struct fs_pin *, struct vfsmount *);
 void pin_kill(struct fs_pin *);
+
+#endif
-- 
2.4.3

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[PATCH 2/6 v5] fs_pin: Export functions for specific filesystem

[Kinglong Mee]

Exports functions for others who want pin to vfsmount,
eg, nfsd's export cache.

v4, v5,
add exporting of pin_kill.

Signed-off-by: Kinglong Mee <kinglongmee-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
---
 fs/fs_pin.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/fs/fs_pin.c b/fs/fs_pin.c
index 611b540..a1a4eb2 100644
--- a/fs/fs_pin.c
+++ b/fs/fs_pin.c
@@ -17,6 +17,7 @@ void pin_remove(struct fs_pin *pin)
 	wake_up_locked(&pin->wait);
 	spin_unlock_irq(&pin->wait.lock);
 }
+EXPORT_SYMBOL(pin_remove);
 
 void pin_insert_group(struct fs_pin *pin, struct vfsmount *m, struct hlist_head *p)
 {
@@ -26,11 +27,13 @@ void pin_insert_group(struct fs_pin *pin, struct vfsmount *m, struct hlist_head
 	hlist_add_head(&pin->m_list, &real_mount(m)->mnt_pins);
 	spin_unlock(&pin_lock);
 }
+EXPORT_SYMBOL(pin_insert_group);
 
 void pin_insert(struct fs_pin *pin, struct vfsmount *m)
 {
 	pin_insert_group(pin, m, &m->mnt_sb->s_pins);
 }
+EXPORT_SYMBOL(pin_insert);
 
 void pin_kill(struct fs_pin *p)
 {
@@ -72,6 +75,7 @@ void pin_kill(struct fs_pin *p)
 	}
 	rcu_read_unlock();
 }
+EXPORT_SYMBOL(pin_kill);
 
 void mnt_pin_kill(struct mount *m)
 {
-- 
2.4.3

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[PATCH 3/6 v5] fs_pin: Kill fs_pin under a reference of vfsmnt

[Kinglong Mee]

v5, new patch

Signed-off-by: Kinglong Mee <kinglongmee-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
---
 fs/namespace.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/fs/namespace.c b/fs/namespace.c
index 1b9e111..3f08a48 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -1049,8 +1049,6 @@ static void cleanup_mnt(struct mount *mnt)
 	 * so mnt_get_writers() below is safe.
 	 */
 	WARN_ON(mnt_get_writers(mnt));
-	if (unlikely(mnt->mnt_pins.first))
-		mnt_pin_kill(mnt);
 	fsnotify_vfsmount_delete(&mnt->mnt);
 	dput(mnt->mnt.mnt_root);
 	deactivate_super(mnt->mnt.mnt_sb);
@@ -1078,6 +1076,7 @@ static DECLARE_DELAYED_WORK(delayed_mntput_work, delayed_mntput);
 
 static void mntput_no_expire(struct mount *mnt)
 {
+put_again:
 	rcu_read_lock();
 	mnt_add_count(mnt, -1);
 	if (likely(mnt->mnt_ns)) { /* shouldn't be the last one */
@@ -1090,6 +1089,13 @@ static void mntput_no_expire(struct mount *mnt)
 		unlock_mount_hash();
 		return;
 	}
+	if (unlikely(mnt->mnt_pins.first)) {
+		mnt_add_count(mnt, 1);
+		rcu_read_unlock();
+		unlock_mount_hash();
+		mnt_pin_kill(mnt);
+		goto put_again;
+	}
 	if (unlikely(mnt->mnt.mnt_flags & MNT_DOOMED)) {
 		rcu_read_unlock();
 		unlock_mount_hash();
-- 
2.4.3

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Re: [PATCH 3/6 v5] fs_pin: Kill fs_pin under a reference of vfsmnt

[J. Bruce Fields]

On Wed, Jun 17, 2015 at 03:51:22PM +0800, Kinglong Mee wrote:
> v5, new patch

I don't know this code at all.  I'll try to give it a proper review.
But could you help me by explaining in some detail what this is doing
and why you're sure it's correct?

--b.

> 
> Signed-off-by: Kinglong Mee <kinglongmee-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
> ---
>  fs/namespace.c | 10 ++++++++--
>  1 file changed, 8 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/namespace.c b/fs/namespace.c
> index 1b9e111..3f08a48 100644
> --- a/fs/namespace.c
> +++ b/fs/namespace.c
> @@ -1049,8 +1049,6 @@ static void cleanup_mnt(struct mount *mnt)
>  	 * so mnt_get_writers() below is safe.
>  	 */
>  	WARN_ON(mnt_get_writers(mnt));
> -	if (unlikely(mnt->mnt_pins.first))
> -		mnt_pin_kill(mnt);
>  	fsnotify_vfsmount_delete(&mnt->mnt);
>  	dput(mnt->mnt.mnt_root);
>  	deactivate_super(mnt->mnt.mnt_sb);
> @@ -1078,6 +1076,7 @@ static DECLARE_DELAYED_WORK(delayed_mntput_work, delayed_mntput);
>  
>  static void mntput_no_expire(struct mount *mnt)
>  {
> +put_again:
>  	rcu_read_lock();
>  	mnt_add_count(mnt, -1);
>  	if (likely(mnt->mnt_ns)) { /* shouldn't be the last one */
> @@ -1090,6 +1089,13 @@ static void mntput_no_expire(struct mount *mnt)
>  		unlock_mount_hash();
>  		return;
>  	}
> +	if (unlikely(mnt->mnt_pins.first)) {
> +		mnt_add_count(mnt, 1);
> +		rcu_read_unlock();
> +		unlock_mount_hash();
> +		mnt_pin_kill(mnt);
> +		goto put_again;
> +	}
>  	if (unlikely(mnt->mnt.mnt_flags & MNT_DOOMED)) {
>  		rcu_read_unlock();
>  		unlock_mount_hash();
> -- 
> 2.4.3
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Re: [PATCH 3/6 v5] fs_pin: Kill fs_pin under a reference of vfsmnt

[Kinglong Mee]

On 6/20/2015 4:29 AM, J. Bruce Fields wrote:
> On Wed, Jun 17, 2015 at 03:51:22PM +0800, Kinglong Mee wrote:
>> v5, new patch
> 
> I don't know this code at all.  I'll try to give it a proper review.
> But could you help me by explaining in some detail what this is doing
> and why you're sure it's correct?

Sorry for my misunderstand of your means in version 4.
I have make a new version as, 

When reference of cahce_head increase(>1), grab a reference of mnt once.
and  reference decrease to 1 (==1), drop the reference of mnt.

So after that,
When ref > 1, user cannot umount the filesystem with -EBUSY.
when ref ==1, means cache only reference by nfsd cache,
no other reference. So user can try umount, 
1. before set MNT_UMOUNT (protected by mount_lock), nfsd cache is
   referenced (ref > 1, legitimize_mntget), umount will fail with -EBUSY.
2. after set MNT_UMOUNT, nfsd cache is referenced (ref == 2),
   legitimize_mntget will fail, and set cache to CACHE_NEGATIVE,
   and the reference will be dropped, re-back to 1.
   So, pin_kill can delete the cache and umount success.
3. when umountting, no reference to nfsd cache, 
   pin_kill can delete the cache and umount success.

thanks,
Kinglong Mee

> 
> --b.
> 
>>
>> Signed-off-by: Kinglong Mee <kinglongmee@gmail.com>
>> ---
>>  fs/namespace.c | 10 ++++++++--
>>  1 file changed, 8 insertions(+), 2 deletions(-)
>>
>> diff --git a/fs/namespace.c b/fs/namespace.c
>> index 1b9e111..3f08a48 100644
>> --- a/fs/namespace.c
>> +++ b/fs/namespace.c
>> @@ -1049,8 +1049,6 @@ static void cleanup_mnt(struct mount *mnt)
>>  	 * so mnt_get_writers() below is safe.
>>  	 */
>>  	WARN_ON(mnt_get_writers(mnt));
>> -	if (unlikely(mnt->mnt_pins.first))
>> -		mnt_pin_kill(mnt);
>>  	fsnotify_vfsmount_delete(&mnt->mnt);
>>  	dput(mnt->mnt.mnt_root);
>>  	deactivate_super(mnt->mnt.mnt_sb);
>> @@ -1078,6 +1076,7 @@ static DECLARE_DELAYED_WORK(delayed_mntput_work, delayed_mntput);
>>  
>>  static void mntput_no_expire(struct mount *mnt)
>>  {
>> +put_again:
>>  	rcu_read_lock();
>>  	mnt_add_count(mnt, -1);
>>  	if (likely(mnt->mnt_ns)) { /* shouldn't be the last one */
>> @@ -1090,6 +1089,13 @@ static void mntput_no_expire(struct mount *mnt)
>>  		unlock_mount_hash();
>>  		return;
>>  	}
>> +	if (unlikely(mnt->mnt_pins.first)) {
>> +		mnt_add_count(mnt, 1);
>> +		rcu_read_unlock();
>> +		unlock_mount_hash();
>> +		mnt_pin_kill(mnt);
>> +		goto put_again;
>> +	}
>>  	if (unlikely(mnt->mnt.mnt_flags & MNT_DOOMED)) {
>>  		rcu_read_unlock();
>>  		unlock_mount_hash();
>> -- 
>> 2.4.3
> .
> 

Re: [PATCH 3/6 v5] fs_pin: Kill fs_pin under a reference of vfsmnt

[Al Viro]

On Wed, Jun 17, 2015 at 03:51:22PM +0800, Kinglong Mee wrote:
> +++ b/fs/namespace.c
> @@ -1049,8 +1049,6 @@ static void cleanup_mnt(struct mount *mnt)
>  	 * so mnt_get_writers() below is safe.
>  	 */
>  	WARN_ON(mnt_get_writers(mnt));
> -	if (unlikely(mnt->mnt_pins.first))
> -		mnt_pin_kill(mnt);
>  	fsnotify_vfsmount_delete(&mnt->mnt);
>  	dput(mnt->mnt.mnt_root);
>  	deactivate_super(mnt->mnt.mnt_sb);
> @@ -1078,6 +1076,7 @@ static DECLARE_DELAYED_WORK(delayed_mntput_work, delayed_mntput);
>  
>  static void mntput_no_expire(struct mount *mnt)
>  {
> +put_again:
>  	rcu_read_lock();
>  	mnt_add_count(mnt, -1);
>  	if (likely(mnt->mnt_ns)) { /* shouldn't be the last one */
> @@ -1090,6 +1089,13 @@ static void mntput_no_expire(struct mount *mnt)
>  		unlock_mount_hash();
>  		return;
>  	}
> +	if (unlikely(mnt->mnt_pins.first)) {
> +		mnt_add_count(mnt, 1);
> +		rcu_read_unlock();
> +		unlock_mount_hash();
> +		mnt_pin_kill(mnt);
> +		goto put_again;
> +	}
>  	if (unlikely(mnt->mnt.mnt_flags & MNT_DOOMED)) {
>  		rcu_read_unlock();
>  		unlock_mount_hash();

This is absolutely wrong.  For one thing, you are running those suckers on
fairly deep stack now, which is a bloody bad idea for a lot reasons -
final mntput() can come with a lot of stack space consumed.  For another,
I'm really not convinced that what you are doing won't bugger the ordering
to hell and back - not without a detailed analysis I don't see in these
patches.

If you want to be able to grab references by those suckers, this is a very
wrong way to go.  Look at legitimize_mnt() for better approach, and yes,
you need to be able to cope with "too late, it's already doomed".  Or you'll
trade those -EBUSY for race with umount(2) returning before the fs shutdown
is complete.
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[PATCH 4/6 v5] path: New helpers path_get_pin/path_put_unpin for path pin

[Kinglong Mee]

Two helpers for filesystem pining to vfsmnt, not mntget.

v4, v5, same as v2.

Signed-off-by: Kinglong Mee <kinglongmee-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
---
 fs/namei.c           | 26 ++++++++++++++++++++++++++
 include/linux/path.h |  4 ++++
 2 files changed, 30 insertions(+)

diff --git a/fs/namei.c b/fs/namei.c
index fe30d3b..8f94e7c 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -492,6 +492,32 @@ void path_put(const struct path *path)
 }
 EXPORT_SYMBOL(path_put);
 
+/**
+ * path_get_pin - get a reference to a path's dentry
+ *                and pin to path's vfsmnt
+ * @path: path to get the reference to
+ * @p: the fs_pin pin to vfsmnt
+ */
+void path_get_pin(struct path *path, struct fs_pin *p)
+{
+	dget(path->dentry);
+	pin_insert_group(p, path->mnt, NULL);
+}
+EXPORT_SYMBOL(path_get_pin);
+
+/**
+ * path_put_unpin - put a reference to a path's dentry
+ *                  and remove pin to path's vfsmnt
+ * @path: path to put the reference to
+ * @p: the fs_pin removed from vfsmnt
+ */
+void path_put_unpin(struct path *path, struct fs_pin *p)
+{
+	dput(path->dentry);
+	pin_remove(p);
+}
+EXPORT_SYMBOL(path_put_unpin);
+
 struct nameidata {
 	struct path	path;
 	struct qstr	last;
diff --git a/include/linux/path.h b/include/linux/path.h
index d137218..34599fb 100644
--- a/include/linux/path.h
+++ b/include/linux/path.h
@@ -3,6 +3,7 @@
 
 struct dentry;
 struct vfsmount;
+struct fs_pin;
 
 struct path {
 	struct vfsmount *mnt;
@@ -12,6 +13,9 @@ struct path {
 extern void path_get(const struct path *);
 extern void path_put(const struct path *);
 
+extern void path_get_pin(struct path *, struct fs_pin *);
+extern void path_put_unpin(struct path *, struct fs_pin *);
+
 static inline int path_equal(const struct path *path1, const struct path *path2)
 {
 	return path1->mnt == path2->mnt && path1->dentry == path2->dentry;
-- 
2.4.3

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[PATCH 5/6 v5] sunrpc: New helper cache_force_expire for cache cleanup

[Kinglong Mee]

Using expiry_time force cleanup a cache.

v5, same v1.

Signed-off-by: Kinglong Mee <kinglongmee-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
---
 include/linux/sunrpc/cache.h | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/include/linux/sunrpc/cache.h b/include/linux/sunrpc/cache.h
index 437ddb6..ce75e9c 100644
--- a/include/linux/sunrpc/cache.h
+++ b/include/linux/sunrpc/cache.h
@@ -210,6 +210,17 @@ extern int cache_check(struct cache_detail *detail,
 		       struct cache_head *h, struct cache_req *rqstp);
 extern void cache_flush(void);
 extern void cache_purge(struct cache_detail *detail);
+
+static inline void cache_force_expire(struct cache_detail *detail, struct cache_head *h)
+{
+	write_lock(&detail->hash_lock);
+	h->expiry_time = seconds_since_boot() - 1;
+	detail->nextcheck = seconds_since_boot();
+	write_unlock(&detail->hash_lock);
+
+	cache_flush();
+}
+
 #define NEVER (0x7FFFFFFF)
 extern void __init cache_initialize(void);
 extern int cache_register_net(struct cache_detail *cd, struct net *net);
-- 
2.4.3

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[PATCH 6/6 v5] nfsd: Allows user un-mounting filesystem where nfsd exports base on

[Kinglong Mee]

If there are some mount points(not exported for nfs) under pseudo root,
after client's operation of those entry under the root, anyone *can't*
unmount those mount points until export cache expired.

/nfs/xfs        *(rw,insecure,no_subtree_check,no_root_squash)
/nfs/pnfs       *(rw,insecure,no_subtree_check,no_root_squash)
total 0
drwxr-xr-x. 3 root root 84 Apr 21 22:27 pnfs
drwxr-xr-x. 3 root root 84 Apr 21 22:27 test
drwxr-xr-x. 2 root root  6 Apr 20 22:01 xfs
Filesystem                      1K-blocks    Used Available Use% Mounted on
......
/dev/sdd                          1038336   32944   1005392   4% /nfs/pnfs
/dev/sdc                         10475520   32928  10442592   1% /nfs/xfs
/dev/sde                           999320    1284    929224   1% /nfs/test
/mnt/pnfs/:
total 0
-rw-r--r--. 1 root root 0 Apr 21 22:23 attr
drwxr-xr-x. 2 root root 6 Apr 21 22:19 tmp

/mnt/xfs/:
total 0
umount: /nfs/test/: target is busy
        (In some cases useful info about processes that
	use the device is found by lsof(8) or fuser(1).)

It's caused by exports cache of nfsd holds the reference of
the path (here is /nfs/test/), so, it can't be umounted.

I don't think that's user expect, they want umount /nfs/test/.
Bruce think user can also umount /nfs/pnfs/ and /nfs/xfs.

Also, using kzalloc for all memory allocating without kmalloc.
Thanks for Al Viro's commets for the logic of fs_pin.

v3,
1. using path_get_pin/path_put_unpin for path pin
2. using kzalloc for memory allocating

v4,
1. add a completion for pin_kill waiting the reference is decreased to zero.
2. add a work_struct for pin_kill decreases the reference indirectly.
3. free svc_export/svc_expkey in pin_kill, not svc_export_put/svc_expkey_put.
4. svc_export_put/svc_expkey_put go though pin_kill logic.

v5, same as v4.

Signed-off-by: Kinglong Mee <kinglongmee-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
---
 fs/nfsd/export.c | 96 +++++++++++++++++++++++++++++++++++++++++++++-----------
 fs/nfsd/export.h | 18 ++++++++++-
 2 files changed, 95 insertions(+), 19 deletions(-)

diff --git a/fs/nfsd/export.c b/fs/nfsd/export.c
index f79521a..d3e59bc 100644
--- a/fs/nfsd/export.c
+++ b/fs/nfsd/export.c
@@ -37,15 +37,23 @@
 #define	EXPKEY_HASHMAX		(1 << EXPKEY_HASHBITS)
 #define	EXPKEY_HASHMASK		(EXPKEY_HASHMAX -1)
 
+static void expkey_destroy(struct svc_expkey *key)
+{
+	auth_domain_put(key->ek_client);
+	kfree_rcu(key, rcu_head);
+}
+
 static void expkey_put(struct kref *ref)
 {
 	struct svc_expkey *key = container_of(ref, struct svc_expkey, h.ref);
 
 	if (test_bit(CACHE_VALID, &key->h.flags) &&
-	    !test_bit(CACHE_NEGATIVE, &key->h.flags))
-		path_put(&key->ek_path);
-	auth_domain_put(key->ek_client);
-	kfree(key);
+	    !test_bit(CACHE_NEGATIVE, &key->h.flags)) {
+		rcu_read_lock();
+		complete(&key->ek_done);
+		pin_kill(&key->ek_pin);
+	} else
+		expkey_destroy(key);
 }
 
 static void expkey_request(struct cache_detail *cd,
@@ -83,7 +91,7 @@ static int expkey_parse(struct cache_detail *cd, char *mesg, int mlen)
 		return -EINVAL;
 	mesg[mlen-1] = 0;
 
-	buf = kmalloc(PAGE_SIZE, GFP_KERNEL);
+	buf = kzalloc(PAGE_SIZE, GFP_KERNEL);
 	err = -ENOMEM;
 	if (!buf)
 		goto out;
@@ -120,6 +128,7 @@ static int expkey_parse(struct cache_detail *cd, char *mesg, int mlen)
 		goto out;
 
 	key.ek_client = dom;	
+	key.cd = cd;
 	key.ek_fsidtype = fsidtype;
 	memcpy(key.ek_fsid, buf, len);
 
@@ -210,6 +219,25 @@ static inline void expkey_init(struct cache_head *cnew,
 	new->ek_fsidtype = item->ek_fsidtype;
 
 	memcpy(new->ek_fsid, item->ek_fsid, sizeof(new->ek_fsid));
+	new->cd = item->cd;
+}
+
+static void expkey_pin_kill(struct fs_pin *pin)
+{
+	struct svc_expkey *key = container_of(pin, struct svc_expkey, ek_pin);
+
+	if (!completion_done(&key->ek_done)) {
+		schedule_work(&key->ek_work);
+		wait_for_completion(&key->ek_done);
+	}
+	path_put_unpin(&key->ek_path, &key->ek_pin);
+	expkey_destroy(key);
+}
+
+static void expkey_close_work(struct work_struct *work)
+{
+	struct svc_expkey *key = container_of(work, struct svc_expkey, ek_work);
+	cache_force_expire(key->cd, &key->h);
 }
 
 static inline void expkey_update(struct cache_head *cnew,
@@ -218,16 +246,19 @@ static inline void expkey_update(struct cache_head *cnew,
 	struct svc_expkey *new = container_of(cnew, struct svc_expkey, h);
 	struct svc_expkey *item = container_of(citem, struct svc_expkey, h);
 
+	init_fs_pin(&new->ek_pin, expkey_pin_kill);
 	new->ek_path = item->ek_path;
-	path_get(&item->ek_path);
+	path_get_pin(&new->ek_path, &new->ek_pin);
 }
 
 static struct cache_head *expkey_alloc(void)
 {
-	struct svc_expkey *i = kmalloc(sizeof(*i), GFP_KERNEL);
-	if (i)
+	struct svc_expkey *i = kzalloc(sizeof(*i), GFP_KERNEL);
+	if (i) {
+		INIT_WORK(&i->ek_work, expkey_close_work);
+		init_completion(&i->ek_done);
 		return &i->h;
-	else
+	} else
 		return NULL;
 }
 
@@ -306,14 +337,21 @@ static void nfsd4_fslocs_free(struct nfsd4_fs_locations *fsloc)
 	fsloc->locations = NULL;
 }
 
-static void svc_export_put(struct kref *ref)
+static void svc_export_destroy(struct svc_export *exp)
 {
-	struct svc_export *exp = container_of(ref, struct svc_export, h.ref);
-	path_put(&exp->ex_path);
 	auth_domain_put(exp->ex_client);
 	nfsd4_fslocs_free(&exp->ex_fslocs);
 	kfree(exp->ex_uuid);
-	kfree(exp);
+	kfree_rcu(exp, rcu_head);
+}
+
+static void svc_export_put(struct kref *ref)
+{
+	struct svc_export *exp = container_of(ref, struct svc_export, h.ref);
+
+	rcu_read_lock();
+	complete(&exp->ex_done);
+	pin_kill(&exp->ex_pin);
 }
 
 static void svc_export_request(struct cache_detail *cd,
@@ -520,7 +558,7 @@ static int svc_export_parse(struct cache_detail *cd, char *mesg, int mlen)
 		return -EINVAL;
 	mesg[mlen-1] = 0;
 
-	buf = kmalloc(PAGE_SIZE, GFP_KERNEL);
+	buf = kzalloc(PAGE_SIZE, GFP_KERNEL);
 	if (!buf)
 		return -ENOMEM;
 
@@ -694,15 +732,34 @@ static int svc_export_match(struct cache_head *a, struct cache_head *b)
 		path_equal(&orig->ex_path, &new->ex_path);
 }
 
+static void export_pin_kill(struct fs_pin *pin)
+{
+	struct svc_export *exp = container_of(pin, struct svc_export, ex_pin);
+
+	if (!completion_done(&exp->ex_done)) {
+		schedule_work(&exp->ex_work);
+		wait_for_completion(&exp->ex_done);
+	}
+	path_put_unpin(&exp->ex_path, &exp->ex_pin);
+	svc_export_destroy(exp);
+}
+
+static void export_close_work(struct work_struct *work)
+{
+	struct svc_export *exp = container_of(work, struct svc_export, ex_work);
+	cache_force_expire(exp->cd, &exp->h);
+}
+
 static void svc_export_init(struct cache_head *cnew, struct cache_head *citem)
 {
 	struct svc_export *new = container_of(cnew, struct svc_export, h);
 	struct svc_export *item = container_of(citem, struct svc_export, h);
 
+	init_fs_pin(&new->ex_pin, export_pin_kill);
 	kref_get(&item->ex_client->ref);
 	new->ex_client = item->ex_client;
 	new->ex_path = item->ex_path;
-	path_get(&item->ex_path);
+	path_get_pin(&new->ex_path, &new->ex_pin);
 	new->ex_fslocs.locations = NULL;
 	new->ex_fslocs.locations_count = 0;
 	new->ex_fslocs.migrated = 0;
@@ -740,10 +797,12 @@ static void export_update(struct cache_head *cnew, struct cache_head *citem)
 
 static struct cache_head *svc_export_alloc(void)
 {
-	struct svc_export *i = kmalloc(sizeof(*i), GFP_KERNEL);
-	if (i)
+	struct svc_export *i = kzalloc(sizeof(*i), GFP_KERNEL);
+	if (i) {
+		INIT_WORK(&i->ex_work, export_close_work);
+		init_completion(&i->ex_done);
 		return &i->h;
-	else
+	} else
 		return NULL;
 }
 
@@ -811,6 +870,7 @@ exp_find_key(struct cache_detail *cd, struct auth_domain *clp, int fsid_type,
 
 	key.ek_client = clp;
 	key.ek_fsidtype = fsid_type;
+	key.cd = cd;
 	memcpy(key.ek_fsid, fsidv, key_len(fsid_type));
 
 	ek = svc_expkey_lookup(cd, &key);
diff --git a/fs/nfsd/export.h b/fs/nfsd/export.h
index 1f52bfc..ff8905d 100644
--- a/fs/nfsd/export.h
+++ b/fs/nfsd/export.h
@@ -4,6 +4,7 @@
 #ifndef NFSD_EXPORT_H
 #define NFSD_EXPORT_H
 
+#include <linux/fs_pin.h>
 #include <linux/sunrpc/cache.h>
 #include <uapi/linux/nfsd/export.h>
 
@@ -46,6 +47,8 @@ struct exp_flavor_info {
 
 struct svc_export {
 	struct cache_head	h;
+	struct cache_detail	*cd;
+
 	struct auth_domain *	ex_client;
 	int			ex_flags;
 	struct path		ex_path;
@@ -58,7 +61,13 @@ struct svc_export {
 	struct exp_flavor_info	ex_flavors[MAX_SECINFO_LIST];
 	enum pnfs_layouttype	ex_layout_type;
 	struct nfsd4_deviceid_map *ex_devid_map;
-	struct cache_detail	*cd;
+
+	struct fs_pin		ex_pin;
+	struct rcu_head		rcu_head;
+
+	/* For cache_put and fs umounting window */
+	struct completion	ex_done;
+	struct work_struct	ex_work;
 };
 
 /* an "export key" (expkey) maps a filehandlefragement to an
@@ -67,12 +76,19 @@ struct svc_export {
  */
 struct svc_expkey {
 	struct cache_head	h;
+	struct cache_detail	*cd;
 
 	struct auth_domain *	ek_client;
 	int			ek_fsidtype;
 	u32			ek_fsid[6];
 
 	struct path		ek_path;
+	struct fs_pin		ek_pin;
+	struct rcu_head		rcu_head;
+
+	/* For cache_put and fs umounting window */
+	struct completion	ek_done;
+	struct work_struct	ek_work;
 };
 
 #define EX_ISSYNC(exp)		(!((exp)->ex_flags & NFSEXP_ASYNC))
-- 
2.4.3

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Re: [PATCH 6/6 v5] nfsd: Allows user un-mounting filesystem where nfsd exports base on

[Al Viro]

On Wed, Jun 17, 2015 at 03:53:12PM +0800, Kinglong Mee wrote:
>  static void expkey_put(struct kref *ref)
>  {
>  	struct svc_expkey *key = container_of(ref, struct svc_expkey, h.ref);
>  
>  	if (test_bit(CACHE_VALID, &key->h.flags) &&
> -	    !test_bit(CACHE_NEGATIVE, &key->h.flags))
> -		path_put(&key->ek_path);
> -	auth_domain_put(key->ek_client);
> -	kfree(key);
> +	    !test_bit(CACHE_NEGATIVE, &key->h.flags)) {
> +		rcu_read_lock();
> +		complete(&key->ek_done);
> +		pin_kill(&key->ek_pin);
> +	} else
> +		expkey_destroy(key);
>  }

> +static void expkey_pin_kill(struct fs_pin *pin)
> +{
> +	struct svc_expkey *key = container_of(pin, struct svc_expkey, ek_pin);
> +
> +	if (!completion_done(&key->ek_done)) {
> +		schedule_work(&key->ek_work);
> +		wait_for_completion(&key->ek_done);
> +	}
> +	path_put_unpin(&key->ek_path, &key->ek_pin);
> +	expkey_destroy(key);
> +}

So basically you want umount(2) to hang until all references are gone.
How long can they stick around and, more to the point, what happens
if some sucker does path_get(&key->ek_path) while umount(2) had been
waiting?  You'll drop the reference to svc_export you'd copied ->ek_path
from and get through the whole dance, letting umount(2) go.

Now what?  Sure, with your previous patch vfsmount will survive - no oopsen
there.  However, you have had umount run to completion, with filesystem
still not shut down.  This is badly broken.

You can't do "I can grab reference at any time until the call of
expkey_pin_kill()" - it's not going to work.  You _must_ grab it
carefully, being ready to cope with "umount has already decided it's
not busy, so it's a goner and we must fail" kind of situations.

You need to
	grab mount_lock with read_seqlock_excl()
	check that vfsmount isn't marked MNT_SYNC_UMOUNT or MNT_DOOMED
and bump refcount in such case; give up on attempt otherwise.
	drop mount_lock
for those attempts to grab the first reference.  And be ready to cope with
failures.
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Re: [PATCH 6/6 v5] nfsd: Allows user un-mounting filesystem where nfsd exports base on

[Kinglong Mee]

On 6/20/2015 5:09 AM, Al Viro wrote:
> On Wed, Jun 17, 2015 at 03:53:12PM +0800, Kinglong Mee wrote:
>>  static void expkey_put(struct kref *ref)
>>  {
>>  	struct svc_expkey *key = container_of(ref, struct svc_expkey, h.ref);
>>  
>>  	if (test_bit(CACHE_VALID, &key->h.flags) &&
>> -	    !test_bit(CACHE_NEGATIVE, &key->h.flags))
>> -		path_put(&key->ek_path);
>> -	auth_domain_put(key->ek_client);
>> -	kfree(key);
>> +	    !test_bit(CACHE_NEGATIVE, &key->h.flags)) {
>> +		rcu_read_lock();
>> +		complete(&key->ek_done);
>> +		pin_kill(&key->ek_pin);
>> +	} else
>> +		expkey_destroy(key);
>>  }
> 
>> +static void expkey_pin_kill(struct fs_pin *pin)
>> +{
>> +	struct svc_expkey *key = container_of(pin, struct svc_expkey, ek_pin);
>> +
>> +	if (!completion_done(&key->ek_done)) {
>> +		schedule_work(&key->ek_work);
>> +		wait_for_completion(&key->ek_done);
>> +	}
>> +	path_put_unpin(&key->ek_path, &key->ek_pin);
>> +	expkey_destroy(key);
>> +}
> 
> So basically you want umount(2) to hang until all references are gone.
> How long can they stick around and, more to the point, what happens
> if some sucker does path_get(&key->ek_path) while umount(2) had been
> waiting?  You'll drop the reference to svc_export you'd copied ->ek_path
> from and get through the whole dance, letting umount(2) go.
> 
> Now what?  Sure, with your previous patch vfsmount will survive - no oopsen
> there.  However, you have had umount run to completion, with filesystem
> still not shut down.  This is badly broken.
> 
> You can't do "I can grab reference at any time until the call of
> expkey_pin_kill()" - it's not going to work.  You _must_ grab it
> carefully, being ready to cope with "umount has already decided it's
> not busy, so it's a goner and we must fail" kind of situations.
> 
> You need to
> 	grab mount_lock with read_seqlock_excl()
> 	check that vfsmount isn't marked MNT_SYNC_UMOUNT or MNT_DOOMED
> and bump refcount in such case; give up on attempt otherwise.
> 	drop mount_lock
> for those attempts to grab the first reference.  And be ready to cope with
> failures.
>

Thanks for your comments,

I have do the work in the new version of 6, also I think I have solve the race
between umount and reference to cache again.

thanks
Kinglong Mee