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

[Junxiao Bi]

> 在 2022年6月4日，下午6:48，Heming Zhao <heming.zhao at suse.com> 写道：
> 
> 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.
Your patch invoked user_dlm_destroy_lock, that will execute also the if and spin lock. Plus function call, that’s not higher cost?

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