mm/ksm: remove redundant code in ksm_fork

Since commit 3c6f33b7 ("mm/ksm: support fork/exec for prctl"), when a
child process is forked, the MMF_VM_MERGE_ANY flag will be inherited in
mm_init(). So, it's unnecessary to set the flag in ksm_fork().

Link: https://lkml.kernel.org/r/20240402024934.1093361-1-tujinjiang@huawei.comSigned-off-by: Jinjiang Tu <tujinjiang@huawei.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
Cc: Nanyong Sun <sunnanyong@huawei.com>
Cc: Rik van Riel <riel@surriel.com>
Cc: Stefan Roesch <shr@devkernel.io>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

include/linux/ksm.h

@@ -45,16 +45,8 @@ static inline void ksm_might_unmap_zero_page(struct mm_struct *mm, pte_t pte)
 
 static inline int ksm_fork(struct mm_struct *mm, struct mm_struct *oldmm)
 {
-	int ret;
-
-	if (test_bit(MMF_VM_MERGEABLE, &oldmm->flags)) {
-		ret = __ksm_enter(mm);
-		if (ret)
-			return ret;
-	}
-
-	if (test_bit(MMF_VM_MERGE_ANY, &oldmm->flags))
-		set_bit(MMF_VM_MERGE_ANY, &mm->flags);
+	if (test_bit(MMF_VM_MERGEABLE, &oldmm->flags))
+		return __ksm_enter(mm);
 
 	return 0;
 }