[PATCH] mm: mark mm_struct.hiwater_rss as data racy

[Ignacio Encinas]

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

Given that this just provides accounting information and that the extra
accuracy isn't worth the potential slowdown, let's annotate is
__data_racy to make KCSAN happy.

Reported-by: syzbot+419c4b42acc36c420ad3@xxxxxxxxxxxxxxxxxxxxxxxxx
Suggested-by: Lorenzo Stoakes <lorenzo.stoakes@xxxxxxxxxx>
Signed-off-by: Ignacio Encinas <ignacio@xxxxxxxxxxxx>
---
Similar issues have been solved in the past [1]. An actual analysis of 
the data race can be found in [2] and [3].

Lorenzo, I added the Suggested-by as your proposal seems roughly
equivalent to what I propose.

[1] https://lore.kernel.org/all/20210913105550.1569419-1-liupeng256@xxxxxxxxxx/T/#u
[2] https://lore.kernel.org/all/900c5035-865d-40b7-8d55-0cbbbc059294@lucifer.local/
[3] https://lore.kernel.org/linux-mm/iwtvhos74gwrk5v5szlosnkusxqp6ubqy6ytkclkucbjwdw4zr@bwxyrwcnybbz/
---
 include/linux/mm_types.h | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 0234f14f2aa6bea42a8a62ccb915c94f556cd3cc..84c86951a978aad07ab4ecefbfff77e7418d8402 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -19,6 +19,7 @@
 #include <linux/workqueue.h>
 #include <linux/seqlock.h>
 #include <linux/percpu_counter.h>
+#include <linux/compiler_types.h>
 
 #include <asm/mmu.h>
 
@@ -939,7 +940,7 @@ struct mm_struct {
 #endif
 
 
-		unsigned long hiwater_rss; /* High-watermark of RSS usage */
+		unsigned long __data_racy hiwater_rss; /* High-watermark of RSS usage */
 		unsigned long hiwater_vm;  /* High-water virtual memory usage */
 
 		unsigned long total_vm;	   /* Total pages mapped */

---
base-commit: 3571e8b091f4270d869dda7a6cc43616c6ad6897
change-id: 20250315-mm-maxrss-data-race-6ce86b0deb14

Best regards,
-- 
Ignacio Encinas <ignacio@xxxxxxxxxxxx>