[merged mm-stable] kasan-fix-quarantine_size-accounting-during-cache-removal.patch removed from -mm tree

[merged mm-stable] kasan-fix-quarantine_size-accounting-during-cache-removal.patch removed from -mm tree

[Andrew Morton]

The quilt patch titled
     Subject: kasan: fix quarantine_size accounting during cache removal
has been removed from the -mm tree.  Its filename was
     kasan-fix-quarantine_size-accounting-during-cache-removal.patch

This patch was dropped because it was merged into the mm-stable branch
of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

------------------------------------------------------
From: Hui Su <sh_def@163.com>
Subject: kasan: fix quarantine_size accounting during cache removal
Date: Tue, 11 Aug 2026 15:33:32 +0800

quarantine_size tracks the total number of bytes stored in
global_quarantine[].  It is incremented when per-CPU quarantine objects
are moved into the global quarantine and decremented when a global batch
is evicted by kasan_quarantine_reduce().

kasan_quarantine_remove_cache() also removes objects from the global
quarantine.  qlist_move_cache() rebuilds the source batch and updates its
.bytes field, but quarantine_size is not adjusted accordingly.

As a result, quarantine_size remains over-counted by the size of the
removed objects.  The stale accounting accumulates across cache removals. 
Once the inflated value exceeds quarantine_max_size,
kasan_quarantine_reduce() can evict a batch even though the actual number
of bytes in global_quarantine[] is still below quarantine_max_size,
shortening the quarantine window.

Fix the accounting by recording each batch's size before
qlist_move_cache() and subtracting the number of bytes actually removed
from quarantine_size while holding quarantine_lock.

A KUnit reproducer used during testing observed the over-count grow by
4698864 bytes after one kasan_quarantine_remove_cache() call with the fix
reverted.  With this change applied, the over-count did not grow.

Link: https://lore.kernel.org/20260811073332.1351893-1-sh_def@163.com
Fixes: 64abdcb24351 ("kasan: eliminate long stalls during quarantine reduction")
Signed-off-by: Hui Su <sh_def@163.com>
Reported-by: Sashiko <sashiko-bot@kernel.org>
Closes: https://sashiko.dev/#/patchset/20260808031459.3032812-1-sh_def%40163.com
Reviewed-by: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Konovalov <andreyknvl@gmail.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Vincenzo Frascino <vincenzo.frascino@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/kasan/quarantine.c |    5 +++++
 1 file changed, 5 insertions(+)

--- a/mm/kasan/quarantine.c~kasan-fix-quarantine_size-accounting-during-cache-removal
+++ a/mm/kasan/quarantine.c
@@ -370,9 +370,14 @@ void kasan_quarantine_remove_cache(struc
 
 	raw_spin_lock_irqsave(&quarantine_lock, flags);
 	for (i = 0; i < QUARANTINE_BATCHES; i++) {
+		size_t old_bytes;
+
 		if (qlist_empty(&global_quarantine[i]))
 			continue;
+		old_bytes = global_quarantine[i].bytes;
 		qlist_move_cache(&global_quarantine[i], &to_free, cache);
+		WRITE_ONCE(quarantine_size, quarantine_size -
+			   (old_bytes - global_quarantine[i].bytes));
 		/* Scanning whole quarantine can take a while. */
 		raw_spin_unlock_irqrestore(&quarantine_lock, flags);
 		cond_resched();
_

Patches currently in -mm which might be from sh_def@163.com are

mm-migrate_device-avoid-out-of-bounds-writes-for-compound-folios.patch