mm/memory-failure.c: rework the try_to_unmap logic in hwpoison_user_mappings()

Only for hugetlb pages in shared mappings, try_to_unmap should take
semaphore in write mode here.  Rework the code to make it clear.

Link: https://lkml.kernel.org/r/20220218090118.1105-7-linmiaohe@huawei.comSigned-off-by: NMiaohe Lin <linmiaohe@huawei.com>
Acked-by: NNaoya Horiguchi <naoya.horiguchi@nec.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

mm/memory-failure.c

@@ -1404,10 +1404,7 @@ static bool hwpoison_user_mappings(struct page *p, unsigned long pfn,
 	if (kill)
 		collect_procs(hpage, &tokill, flags & MF_ACTION_REQUIRED);
 
-	if (!PageHuge(hpage)) {
-		try_to_unmap(hpage, ttu);
-	} else {
-		if (!PageAnon(hpage)) {
+	if (PageHuge(hpage) && !PageAnon(hpage)) {
 		/*
 		 * For hugetlb pages in shared mappings, try_to_unmap
 		 * could potentially call huge_pmd_unshare.  Because of
@@ -1424,7 +1421,6 @@ static bool hwpoison_user_mappings(struct page *p, unsigned long pfn,
 	} else {
 		try_to_unmap(hpage, ttu);
 	}
-	}
 
 	unmap_success = !page_mapped(hpage);
 	if (!unmap_success)