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

@@ -1404,26 +1404,22 @@ 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);
+	if (PageHuge(hpage) && !PageAnon(hpage)) {
+		/*
+		 * For hugetlb pages in shared mappings, try_to_unmap
+		 * could potentially call huge_pmd_unshare.  Because of
+		 * this, take semaphore in write mode here and set
+		 * TTU_RMAP_LOCKED to indicate we have taken the lock
+		 * at this higher level.
+		 */
+		mapping = hugetlb_page_mapping_lock_write(hpage);
+		if (mapping) {
+			try_to_unmap(hpage, ttu|TTU_RMAP_LOCKED);
+			i_mmap_unlock_write(mapping);
+		} else
+			pr_info("Memory failure: %#lx: could not lock mapping for mapped huge page\n", pfn);
 	} else {
-		if (!PageAnon(hpage)) {
-			/*
-			 * For hugetlb pages in shared mappings, try_to_unmap
-			 * could potentially call huge_pmd_unshare.  Because of
-			 * this, take semaphore in write mode here and set
-			 * TTU_RMAP_LOCKED to indicate we have taken the lock
-			 * at this higher level.
-			 */
-			mapping = hugetlb_page_mapping_lock_write(hpage);
-			if (mapping) {
-				try_to_unmap(hpage, ttu|TTU_RMAP_LOCKED);
-				i_mmap_unlock_write(mapping);
-			} else
-				pr_info("Memory failure: %#lx: could not lock mapping for mapped huge page\n", pfn);
-		} else {
-			try_to_unmap(hpage, ttu);
-		}
+		try_to_unmap(hpage, ttu);
 	}
 
 	unmap_success = !page_mapped(hpage);