David Wysochanski [off-list ref] wrote:

quoted

 (4) fscache_enable/disable_cookie() have been removed.

     Call fscache_use_cookie() and fscache_unuse_cookie() when a file is
     opened or closed to prevent a cache file from being culled and to keep
     resources to hand that are needed to do I/O.

     Unuse the cookie when a file is opened for writing.  This is gated by
     the NFS_INO_FSCACHE flag on the nfs_inode.

     A better way might be to invalidate it with FSCACHE_INVAL_DIO_WRITE
     which will keep it unused until all open files are closed.

It looks like the comment doesn't match what was actually done inside
nfs_fscache_open_file().  Is the code right and the comment just out of date?

The comment is out of date.  NFS_INO_FSCACHE isn't used now.

I'm getting that kasan UAF firing periodically in this code path, and so it
looks related to this change,though I don't have great info on it so far and
it's hard to reproduce.

Can you copy the kasan UAF text into a reply?

David