CVE-2021-46937

In the Linux kernel, the following vulnerability has been resolved:
mm/damon/dbgfs: fix ‘struct pid’ leaks in ‘dbgfs_target_ids_write()’ DAMON
debugfs interface increases the reference counts of 'struct pid’s for
targets from the ‘target_ids’ file write callback
(‘dbgfs_target_ids_write()’), but decreases the counts only in DAMON
monitoring termination callback (‘dbgfs_before_terminate()’). Therefore,
when ‘target_ids’ file is repeatedly written without DAMON monitoring
start/termination, the reference count is not decreased and therefore
memory for the ‘struct pid’ cannot be freed. This commit fixes this issue
by decreasing the reference counts when ‘target_ids’ is written.