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

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Message-ID: <1d56b79c-1c2b-b988-7861-6b80df1d0a20@suse.com>
Date:   Mon, 16 Jan 2017 11:06:13 +0800
From:   Eric Ren <zren@...e.com>
To:     Junxiao Bi <junxiao.bi@...cle.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

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;-)

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;
>>>>    }
>>>>
>