Re: [Ocfs2-devel] [PATCH 2/2] ocfs2: fix deadlocks when taking inode lock at vfs entry points

[Joseph Qi]

On 17/1/12 19:24, Eric Ren wrote:
> Hi Joseph,
>
> On 01/09/2017 10:13 AM, Eric Ren wrote:
> > > > > So you are trying to fix it by making phase3 finish without really 
> > > > > doing
> > > > Phase3 can go ahead because this node is already under protection 
> > > > of cluster lock.
> > > You said it was blocked...
> > Oh, sorry, I meant phase3 can go ahead if this patch set is applied;-)
> >
> > > "Another hand, the recursive cluster lock (the second one) will be 
> > > blocked in
> > > __ocfs2_cluster_lock() because of OCFS2_LOCK_BLOCKED."
> > > > > __ocfs2_cluster_lock, then Process B can continue either.
> > > > > Let us bear in mind that phase1 and phase3 are in the same context 
> > > > > and
> > > > > executed in order. That's why I think there is no need to check if 
> > > > > locked
> > > > > by myself in phase1.
> > Sorry, I still cannot see it. Without keeping track of the first 
> > cluster lock, how can we
> > know if
> > we are under a context that has already been in the protecting of 
> > cluster lock? How can we
> > handle
> > the recursive locking (the second cluster lock) if we don't have this 
> > information?
> > > > > If phase1 finds it is already locked by myself, that means the holder
> > > > > is left by last operation without dec holder. That's why I think 
> > > > > it is a bug
> > > > > instead of a recursive lock case.
> > I think I got your point here. Do you mean that we should just add 
> > the lock holder at the
> > first locking position
> > without checking before that? Unfortunately, it's tricky here to know 
> > exactly which ocfs2
> > routine will be the first vfs
> > entry point, such as ocfs2_get_acl() which can be both the first vfs 
> > entry point and the
> > second vfs entry point after
> > ocfs2_permission(), right?
> >
> > It will be a coding bug if the problem you concern about happens. I 
> > think we don't need to
> > worry about this much because
> > the code logic here is quite simple;-)
> Ping...
>
> Did I clear your doubts by the last email? I really want to get your 
> point, if not.
>
> If there's any problem, I will fix them in the next version;-)
Yes, but I still worry about the code bug case will be hidden behind 
recursive lock...
Anyway, It depends on others...

Thanks,
Joseph
> Thanks,
> Eric
>
> > Thanks for your patience!
> > Eric
> >
> > > > D