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

[Eric Ren]

On 01/16/2017 11:13 AM, Junxiao Bi wrote:
> 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.

Yes! I like this idea, will add it in next version, thanks!

Eric

> 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;
> > > > > >     }