[PATCH v2 4/6] mm: Switch dump_page to get_kernel_nofault

["Matthew Wilcox (Oracle)" <willy@xxxxxxxxxxxxx>]

This is simpler to use than copy_from_kernel_nofault().  Also
make some of the related error messages less verbose.

Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
---
 mm/debug.c | 36 ++++++++++++++++--------------------
 1 file changed, 16 insertions(+), 20 deletions(-)

diff --git a/mm/debug.c b/mm/debug.c
index d2ffc926d8f5..fb64ff7454b6 100644
--- a/mm/debug.c
+++ b/mm/debug.c
@@ -109,54 +109,50 @@ void __dump_page(struct page *page, const char *reason)
 	else if (PageAnon(page))
 		type = "anon ";
 	else if (mapping) {
-		const struct inode *host;
+		struct inode *host;
 		const struct address_space_operations *a_ops;
-		const struct hlist_node *dentry_first;
-		const struct dentry *dentry_ptr;
+		struct hlist_node *dentry_first;
+		struct dentry *dentry_ptr;
 		struct dentry dentry;
 
 		/*
 		 * mapping can be invalid pointer and we don't want to crash
 		 * accessing it, so probe everything depending on it carefully
 		 */
-		if (copy_from_kernel_nofault(&host, &mapping->host,
-					sizeof(struct inode *)) ||
-		    copy_from_kernel_nofault(&a_ops, &mapping->a_ops,
-				sizeof(struct address_space_operations *))) {
-			pr_warn("failed to read mapping->host or a_ops, mapping not a valid kernel address?\n");
+		if (get_kernel_nofault(host, &mapping->host) ||
+		    get_kernel_nofault(a_ops, &mapping->a_ops)) {
+			pr_warn("failed to read mapping contents, not a valid kernel address?\n");
 			goto out_mapping;
 		}
 
 		if (!host) {
-			pr_warn("mapping->a_ops:%ps\n", a_ops);
+			pr_warn("aops:%ps\n", a_ops);
 			goto out_mapping;
 		}
 
-		if (copy_from_kernel_nofault(&dentry_first,
-			&host->i_dentry.first, sizeof(struct hlist_node *))) {
-			pr_warn("mapping->a_ops:%ps with invalid mapping->host inode address %px\n",
-				a_ops, host);
+		if (get_kernel_nofault(dentry_first, &host->i_dentry.first)) {
+			pr_warn("aops:%ps with invalid host inode %px\n",
+					a_ops, host);
 			goto out_mapping;
 		}
 
 		if (!dentry_first) {
-			pr_warn("mapping->a_ops:%ps\n", a_ops);
+			pr_warn("aops:%ps\n", a_ops);
 			goto out_mapping;
 		}
 
 		dentry_ptr = container_of(dentry_first, struct dentry, d_u.d_alias);
-		if (copy_from_kernel_nofault(&dentry, dentry_ptr,
-							sizeof(struct dentry))) {
-			pr_warn("mapping->aops:%ps with invalid mapping->host->i_dentry.first %px\n",
-				a_ops, dentry_ptr);
+		if (get_kernel_nofault(dentry, dentry_ptr)) {
+			pr_warn("aops:%ps with invalid dentry %px\n", a_ops,
+					dentry_ptr);
 		} else {
 			/*
 			 * if dentry is corrupted, the %pd handler may still
 			 * crash, but it's unlikely that we reach here with a
 			 * corrupted struct page
 			 */
-			pr_warn("mapping->aops:%ps dentry name:\"%pd\"\n",
-								a_ops, &dentry);
+			pr_warn("aops:%ps dentry name:\"%pd\"\n", a_ops,
+					&dentry);
 		}
 	}
 out_mapping:
-- 
2.27.0