Re: [PATCH] mm: cleancache: fix potential race in cleancache apis

[Matthew Wilcox]

On Wed, Jun 30, 2021 at 10:13:28AM +0200, gregkh@xxxxxxxxxxxxxxxxxxx wrote:
> On Wed, Jun 30, 2021 at 04:33:10PM +0900, 권오훈 wrote:
> > Current cleancache api implementation has potential race as follows,
> > which might lead to corruption in filesystems using cleancache.
> > 
> > thread 0                thread 1                        thread 2
> > 
> >                         in put_page
> >                         get pool_id K for fs1
> > invalidate_fs on fs1
> > frees pool_id K
> >                                                         init_fs for fs2
> >                                                         allocates pool_id K
> >                         put_page puts page
> >                         which belongs to fs1
> >                         into cleancache pool for fs2
> > 
> > At this point, a file cache which originally belongs to fs1 might be
> > copied back to cleancache pool of fs2, which might be later used as if
> > it were normal cleancache of fs2, and could eventually corrupt fs2 when
> > flushed back.
> > 
> > Add rwlock in order to synchronize invalidate_fs with other cleancache
> > operations.
> > 
> > In normal situations where filesystems are not frequently mounted or
> > unmounted, there will be little performance impact since
> > read_lock/read_unlock apis are used.
> > 
> > Signed-off-by: Ohhoon Kwon <ohoono.kwon@xxxxxxxxxxx>
> 
> What commit does this fix?  Should it go to stable kernels?

I have a commit I haven't submitted yet with this changelog:

    Remove cleancache

    The last cleancache backend was deleted in v5.3 ("xen: remove tmem
    driver"), so it has been unused since.  Remove all its filesystem hooks.

    Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>