This was fixed in Ubuntu-5.4.0-80.90 by:
Author: Anna Schumaker <email address hidden> Date: Wed May 19 12:54:51 2021 -0400 NFSv4: Fix a NULL pointer dereference in pnfs_mark_matching_lsegs_return()
For 5.11 this is pending release as Ubuntu-5.11.0-26.28 (currently in -proposed).
This was fixed in Ubuntu-5.4.0-80.90 by:
Author: Anna Schumaker <email address hidden> matching_ lsegs_return( )
Date: Wed May 19 12:54:51 2021 -0400
NFSv4: Fix a NULL pointer dereference in pnfs_mark_
For 5.11 this is pending release as Ubuntu-5.11.0-26.28 (currently in -proposed).