locks use-after-free stable request

[Mark Salyzyn]

Referencing upstream fixes commit 
dcf23ac3e846ca0cf626c155a0e3fcbbcf4fae8a ("locks: reinstate 
locks_delete_block optimization") and commit 
6d390e4b5d48ec03bb87e63cf0a2bff5f4e116da ("locks: fix a potential 
use-after-free problem when wakeup a waiter") and possibly address 
CVE-2019-19769.

Please apply to all relevant stable trees including 5.4, 4.19 and below. 
Confirmed they apply cleanly to 5.4 and 4.19.


Signed-off-by: Mark Salyzyn <salyzyn@xxxxxxxxxxx>

Cc: stable@xxxxxxxxxxxxxxx

Cc: linux-kernel@xxxxxxxxxxxxxxx

Cc: kernel-team@xxxxxxxxxxx