mm: annotate data race in update_hiwater_rss

mm_struct.hiwater_rss can be accessed concurrently without proper
synchronization as reported by KCSAN.

This data race is benign as it only affects accounting information.
Annotate it with data_race() to make KCSAN happy.

Link: https://lkml.kernel.org/r/20250331-mm-maxrss-data-race-v2-1-cf958e6205bf@iencinas.com


Signed-off-by: Ignacio Encinas <ignacio@iencinas.com>
Reported-by:  <syzbot+419c4b42acc36c420ad3@syzkaller.appspotmail.com>
Closes: https://lore.kernel.org/all/67e3390c.050a0220.1ec46.0001.GAE@google.com/


Suggested-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Acked-by: Pedro Falcato <pfalcato@suse.de>
Cc: Liam Howlett <liam.howlett@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>