linux-kernel - Re: [PATCH 2/2] ocfs2: fix deadlocks when taking inode lock at vfs entry points

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Message-ID: <d0585955-51fa-653d-94f3-51ca59e29453@oracle.com>
Date:   Mon, 16 Jan 2017 11:13:19 +0800
From:   Junxiao Bi <junxiao.bi@...cle.com>
To:     Eric Ren <zren@...e.com>, ocfs2-devel@....oracle.com
Cc:     akpm@...ux-foundation.org, mfasheh@...sity.com, jlbec@...lplan.org,
        ghe@...e.com, jiangqi903@...il.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] ocfs2: fix deadlocks when taking inode lock at vfs
 entry points

On 01/16/2017 11:06 AM, Eric Ren wrote:
> Hi Junxiao,
> 
> On 01/16/2017 10:46 AM, Junxiao Bi wrote:
>>>> If had_lock==true, it is a bug? I think we should BUG_ON for it, that
>>>> can help us catch bug at the first time.
>>> Good idea! But I'm not sure if "ocfs2_setattr" is always the first one
>>> who takes the cluster lock.
>>> It's harder for me to name all the possible paths;-/
>> The BUG_ON() can help catch the path where ocfs2_setattr is not the
>> first one.
> Yes, I understand. But, the problem is that the vfs entries calling
> order is out of our control.
> I don't want to place an assertion where I'm not 100% sure it's
> absolutely right;-)
If it is not the first one, is it another recursive locking bug? In this
case, if you don't like BUG_ON(), you can dump the call trace and print
some warning message.

Thanks,
Junxiao.
> 
> Thanks,
> Eric
> 
>>
>> Thanks,
>> Junxiao.
>>
>>>>
>>>>> +    if (had_lock)
>>>>> +        arg_flags = OCFS2_META_LOCK_GETBH;
>>>>> +    status = ocfs2_inode_lock_full(inode, &bh, 1, arg_flags);
>>>>>        if (status < 0) {
>>>>>            if (status != -ENOENT)
>>>>>                mlog_errno(status);
>>>>>            goto bail_unlock_rw;
>>>>>        }
>>>>> -    inode_locked = 1;
>>>>> +    if (!had_lock) {
>>>>> +        ocfs2_add_holder(lockres, &oh);
>>>>> +        inode_locked = 1;
>>>>> +    }
>>>>>          if (size_change) {
>>>>>            status = inode_newsize_ok(inode, attr->ia_size);
>>>>> @@ -1260,7 +1270,8 @@ int ocfs2_setattr(struct dentry *dentry, struct
>>>>> iattr *attr)
>>>>>    bail_commit:
>>>>>        ocfs2_commit_trans(osb, handle);
>>>>>    bail_unlock:
>>>>> -    if (status) {
>>>>> +    if (status && inode_locked) {
>>>>> +        ocfs2_remove_holder(lockres, &oh);
>>>>>            ocfs2_inode_unlock(inode, 1);
>>>>>            inode_locked = 0;
>>>>>        }
>>>>> @@ -1278,8 +1289,10 @@ int ocfs2_setattr(struct dentry *dentry,
>>>>> struct iattr *attr)
>>>>>            if (status < 0)
>>>>>                mlog_errno(status);
>>>>>        }
>>>>> -    if (inode_locked)
>>>>> +    if (inode_locked) {
>>>>> +        ocfs2_remove_holder(lockres, &oh);
>>>>>            ocfs2_inode_unlock(inode, 1);
>>>>> +    }
>>>>>          brelse(bh);
>>>>>        return status;
>>>>> @@ -1321,20 +1334,31 @@ int ocfs2_getattr(struct vfsmount *mnt,
>>>>>    int ocfs2_permission(struct inode *inode, int mask)
>>>>>    {
>>>>>        int ret;
>>>>> +    int has_locked;
>>>>> +    struct ocfs2_holder oh;
>>>>> +    struct ocfs2_lock_res *lockres;
>>>>>          if (mask & MAY_NOT_BLOCK)
>>>>>            return -ECHILD;
>>>>>    -    ret = ocfs2_inode_lock(inode, NULL, 0);
>>>>> -    if (ret) {
>>>>> -        if (ret != -ENOENT)
>>>>> -            mlog_errno(ret);
>>>>> -        goto out;
>>>>> +    lockres = &OCFS2_I(inode)->ip_inode_lockres;
>>>>> +    has_locked = (ocfs2_is_locked_by_me(lockres) != NULL);
>>>> The same thing as ocfs2_setattr.
>>> OK. I will think over your suggestions!
>>>
>>> Thanks,
>>> Eric
>>>
>>>> Thanks,
>>>> Junxiao.
>>>>> +    if (!has_locked) {
>>>>> +        ret = ocfs2_inode_lock(inode, NULL, 0);
>>>>> +        if (ret) {
>>>>> +            if (ret != -ENOENT)
>>>>> +                mlog_errno(ret);
>>>>> +            goto out;
>>>>> +        }
>>>>> +        ocfs2_add_holder(lockres, &oh);
>>>>>        }
>>>>>          ret = generic_permission(inode, mask);
>>>>>    -    ocfs2_inode_unlock(inode, 0);
>>>>> +    if (!has_locked) {
>>>>> +        ocfs2_remove_holder(lockres, &oh);
>>>>> +        ocfs2_inode_unlock(inode, 0);
>>>>> +    }
>>>>>    out:
>>>>>        return ret;
>>>>>    }
>>>>>
>>
>