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>

diff --git a/include/linux/mm.h b/include/linux/mm.h
index dcdb798..1690f21 100644 (file)
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -12,6 +12,7 @@
 #include <linux/rbtree.h>
 #include <linux/atomic.h>
 #include <linux/debug_locks.h>
+#include <linux/compiler.h>
 #include <linux/mm_types.h>
 #include <linux/mmap_lock.h>
 #include <linux/range.h>
@@ -2796,7 +2797,7 @@ static inline void update_hiwater_rss(struct mm_struct *mm)
 {
        unsigned long _rss = get_mm_rss(mm);
 
-       if ((mm)->hiwater_rss < _rss)
+       if (data_race(mm->hiwater_rss) < _rss)
                (mm)->hiwater_rss = _rss;
 }