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SubjectRe: [PATCH] mm: cleancache: fix potential race in cleancache apis
On Wed, Jun 30, 2021 at 12:26:57PM +0100, Matthew Wilcox wrote:
> On Wed, Jun 30, 2021 at 10:13:28AM +0200, gregkh@linuxfoundation.org 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@samsung.com>
> >
> > 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@infradead.org>

That's even better!

But if so, how is the above reported problem even a problem if no one is
using cleancache?

thanks,

greg k-h

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