• Benjamin Coddington's avatar
    NFSv4: Wait for stateid updates after CLOSE/OPEN_DOWNGRADE · b4868b44
    Benjamin Coddington authored
    Since commit 0e0cb35b ("NFSv4: Handle NFS4ERR_OLD_STATEID in
    CLOSE/OPEN_DOWNGRADE") the following livelock may occur if a CLOSE races
    with the update of the nfs_state:
    
    Process 1           Process 2           Server
    =========           =========           ========
     OPEN file
                        OPEN file
                                            Reply OPEN (1)
                                            Reply OPEN (2)
     Update state (1)
     CLOSE file (1)
                                            Reply OLD_STATEID (1)
     CLOSE file (2)
                                            Reply CLOSE (-1)
                        Update state (2)
                        wait for state change
     OPEN file
                        wake
     CLOSE file
     OPEN file
                        wake
     CLOSE file
     ...
                        ...
    
    We can avoid this situation by not issuing an immediate retry with a bumped
    seqid when CLOSE/OPEN_DOWNGRADE receives NFS4ERR_OLD_STATEID.  Instead,
    take the same approach used by OPEN and wait at least 5 seconds for
    outstanding stateid updates to complete if we can detect that we're out of
    sequence.
    
    Note that after this change it is still possible (though unlikely) that
    CLOSE waits a full 5 seconds, bumps the seqid, and retries -- and that
    attempt races with another OPEN at the same time.  In order to avoid this
    race (which would result in the livelock), update
    nfs_need_update_open_stateid() to handle the case where:
     - the state is NFS_OPEN_STATE, and
     - the stateid doesn't match the current open stateid
    
    Finally, nfs_need_update_open_stateid() is modified to be idempotent and
    renamed to better suit the purpose of signaling that the stateid passed
    is the next stateid in sequence.
    
    Fixes: 0e0cb35b ("NFSv4: Handle NFS4ERR_OLD_STATEID in CLOSE/OPEN_DOWNGRADE")
    Cc: stable@vger.kernel.org # v5.4+
    Signed-off-by: default avatarBenjamin Coddington <bcodding@redhat.com>
    Signed-off-by: default avatarAnna Schumaker <Anna.Schumaker@Netapp.com>
    b4868b44
nfs4trace.h 64.8 KB