On Thu, Jul 01, 2021 at 02:06:44PM +0900, 권오훈 wrote:

On Thu, Jul 1, 2021 at 02:06:45PM +0900, 권오훈 wrote:

quoted

On Wed, Jun 30, 2021 at 12:26:57PM +0100, Matthew Wilcox wrote:

quoted

On Wed, Jun 30, 2021 at 10:13:28AM +0200, gregkh@linuxfoundation.org wrote:

quoted

On Wed, Jun 30, 2021 at 04:33:10PM +0900, 권오훈 wrote:

quoted

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 <redacted>

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) [off-list ref]

 
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

Dear all.

We are using Cleancache APIs for our proprietary feature in Samsung.
As Wilcox mentioned, however, there is no cleancache backend in current kernel
mainline.
So if the race patch shall be accepted, then it seems unnecessary to patch 
previous stable kernels.

Meanwhile, I personally think cleancache API still has potential to be a good
material when used with new arising technologies such as pmem or NVMe.

So I suggest to postpone removing cleancache for a while.

If there are no in-kernel users, it needs to be removed.  If you rely on
this, wonderful, please submit your code as soon as possible.

thanks,

greg k-h