[Ocfs2-devel] [PATCH] ocfs2: kill EBUSY from dlmfs_evict_inode

[Heming Zhao]

sorry for my last reply. thunderbird messed up format. I resend my reply
with neomutt, please check it.
(no new change between the last messed-up mail and this mail.)

On Sun, Jun 05, 2022 at 12:48:18AM +0000, Junxiao Bi wrote:
> 
> 
> > 在 2022年6月4日，下午4:17，heming.zhao at suse.com 写道：
> > 
> > On 6/5/22 06:27, Junxiao Bi wrote:
> >>> On 6/4/22 3:10 AM, heming.zhao at suse.com wrote:
> >>> Hello Junxiao,
> >>> 
> >>> On 6/4/22 06:31, Junxiao Bi via Ocfs2-devel wrote:
> >>>> When unlink a dlmfs, first it will invoke dlmfs_unlink(), and then invoke
> >>>> dlmfs_evict_inode(), user_dlm_destroy_lock() is invoked in both places,
> >>>> the second one from dlmfs_evict_inode() will get EBUSY error because
> >>>> USER_LOCK_IN_TEARDOWN is already set in lockres. This doesn't affect
> >>>> any function, just the error log is anonying.
> >>>> 
> >>>> Signed-off-by: Junxiao Bi <junxiao.bi at oracle.com>
> >>>> ---
> >>>>   fs/ocfs2/dlmfs/dlmfs.c | 14 +++++++++++---
> >>>>   1 file changed, 11 insertions(+), 3 deletions(-)
> >>>> 
> >>>> diff --git a/fs/ocfs2/dlmfs/dlmfs.c b/fs/ocfs2/dlmfs/dlmfs.c
> >>>> index e360543ad7e7..a120610dff7e 100644
> >>>> --- a/fs/ocfs2/dlmfs/dlmfs.c
> >>>> +++ b/fs/ocfs2/dlmfs/dlmfs.c
> >>>> @@ -296,17 +296,25 @@ static void dlmfs_evict_inode(struct inode *inode)
> >>>>   {
> >>>>       int status;
> >>>>       struct dlmfs_inode_private *ip;
> >>>> +    struct user_lock_res *lockres;
> >>>> +    int destroyed;
> >>>>         clear_inode(inode);
> >>>>         mlog(0, "inode %lu\n", inode->i_ino);
> >>>>         ip = DLMFS_I(inode);
> >>>> +    lockres = &ip->ip_lockres;
> >>>>         if (S_ISREG(inode->i_mode)) {
> >>>> -        status = user_dlm_destroy_lock(&ip->ip_lockres);
> >>>> -        if (status < 0)
> >>>> -            mlog_errno(status);
> >>>> +        spin_lock(&lockres->l_lock);
> >>>> +        destroyed = !!(lockres->l_flags & USER_LOCK_IN_TEARDOWN);
> >>>> +        spin_unlock(&lockres->l_lock);
> >>> 
> >>> This area code does the same work in user_dlm_destroy_lock(). Why not to give another
> >>> errno (e.g -EAGAIN) for user_dlm_destroy_lock when l_flags contains USER_LOCK_IN_TEARDOWN.
> >>> then change 'if (status < 0)' to 'if (status < 0 && status != -EAGAIN)'
> >> I don't think we should do that. It's reasonable for user_dlm_destroy_lock() to return EBUSY in that case. EAGAIN is for the case, you invoke it second time you may succeed. That's not the case here.
> > 
> > I agree the EAGAIN is not good, but do you think the errno idea is reasonable?
> > user_dlm_destroy_lock only has two callers: dlmfs_evict_inode & dlmfs_unlink.
> > the code logic is clear, we can choose another errno, or even create a new one.
> > it costs too much to use spin_lock to avoid print an error log.
> Regarding cost, the suggested way has even higher cost, the spin lock can’t be avoided unless you don’t access the lockres and an extra function call was also added.
> Actually that function shouldn’t be invoked because it was already invoked once in this flow. I don’t think we should change return value of that function, EBUSY looks most reasonable return value for me.

I can't see why my idea cost more. 
The patch ('NEW_ERRNO' should be changed) with my idea:

diff --git a/fs/ocfs2/dlmfs/dlmfs.c b/fs/ocfs2/dlmfs/dlmfs.c
index e360543ad7e7..dd47556b07fa 100644
--- a/fs/ocfs2/dlmfs/dlmfs.c
+++ b/fs/ocfs2/dlmfs/dlmfs.c
@@ -305,7 +305,7 @@ static void dlmfs_evict_inode(struct inode *inode)

     if (S_ISREG(inode->i_mode)) {
         status = user_dlm_destroy_lock(&ip->ip_lockres);
-        if (status < 0)
+        if (status < 0 && status != -NEW_ERRNO)
             mlog_errno(status);
         iput(ip->ip_parent);
         goto clear_fields;
diff --git a/fs/ocfs2/dlmfs/userdlm.c b/fs/ocfs2/dlmfs/userdlm.c
index 617c92e7b925..93b8d7bad96e 100644
--- a/fs/ocfs2/dlmfs/userdlm.c
+++ b/fs/ocfs2/dlmfs/userdlm.c
@@ -600,6 +600,7 @@ int user_dlm_destroy_lock(struct user_lock_res
*lockres)
     spin_lock(&lockres->l_lock);
     if (lockres->l_flags & USER_LOCK_IN_TEARDOWN) {
         spin_unlock(&lockres->l_lock);
+        status = -NEW_ERRNO;
         goto bail;
     } 

your patch added many codes and add another 'if' branch.
- the many codes: cpu will spend more time to complete the same work.
- the new added 'if' branch will breaks cpu pipeline.

my patch only changes 2 lines, maybe add 2 lines cpu instruct without adding
new breaking cpu pipeline case.

/Heming

> >>> 
> >>>> +        if (!destroyed) {
> >>>> +            status = user_dlm_destroy_lock(lockres);
> >>>> +            if (status < 0)
> >>>> +                mlog_errno(status);
> >>>> +        }
> >>>>           iput(ip->ip_parent);
> >>>>           goto clear_fields;
> >>>>       }
> >>> 
> >