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@xxxxxxxxx>
>> ---
>> 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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