Return-Path: Received: from mail-pd0-f178.google.com ([209.85.192.178]:36531 "EHLO mail-pd0-f178.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750993AbbFYOO5 (ORCPT ); Thu, 25 Jun 2015 10:14:57 -0400 Message-ID: <558C0CD2.609@gmail.com> Date: Thu, 25 Jun 2015 22:14:42 +0800 From: Kinglong Mee MIME-Version: 1.0 To: "J. Bruce Fields" CC: Al Viro , "linux-nfs@vger.kernel.org" , linux-fsdevel@vger.kernel.org, NeilBrown , Trond Myklebust , kinglongmee@gmail.com Subject: Re: [PATCH 3/6 v5] fs_pin: Kill fs_pin under a reference of vfsmnt References: <5581266C.9080404@gmail.com> <558126FA.8050608@gmail.com> <20150619202916.GE21903@fieldses.org> In-Reply-To: <20150619202916.GE21903@fieldses.org> Content-Type: text/plain; charset=windows-1252 Sender: linux-nfs-owner@vger.kernel.org List-ID: 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 >> --- >> 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 > . >