kasan: prevent cpu_quarantine corruption when CPU offline and cache shrink occur at same time

kasan_quarantine_remove_cache() is called in kmem_cache_shrink()/
destroy().  The kasan_quarantine_remove_cache() call is protected by
cpuslock in kmem_cache_destroy() to ensure serialization with
kasan_cpu_offline().

However the kasan_quarantine_remove_cache() call is not protected by
cpuslock in kmem_cache_shrink().  When a CPU is going offline and cache
shrink occurs at same time, the cpu_quarantine may be corrupted by
interrupt (per_cpu_remove_cache operation).

So add a cpu_quarantine offline flags check in per_cpu_remove_cache().

[[email protected]: add comment, per Zqiang]

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Zqiang <[email protected]>
Reviewed-by: Dmitry Vyukov <[email protected]>
Cc: Andrey Ryabinin <[email protected]>
Cc: Alexander Potapenko <[email protected]>
Cc: Andrey Konovalov <[email protected]>
Cc: <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

Author: qiangzh3

mm/kasan/quarantine.c

@@ -315,6 +315,13 @@ static void per_cpu_remove_cache(void *arg)
 	struct qlist_head *q;
 
 	q = this_cpu_ptr(&cpu_quarantine);
+	/*
+	 * Ensure the ordering between the writing to q->offline and
+	 * per_cpu_remove_cache.  Prevent cpu_quarantine from being corrupted
+	 * by interrupt.
+	 */
+	if (READ_ONCE(q->offline))
+		return;
 	qlist_move_cache(q, &to_free, cache);
 	qlist_free_all(&to_free, cache);
 }