[PATCH 15/15] mm: replace remaining &folio->page uses with folio_page() and helpers

[Nilay Vaish <nilayvaish@google.com>]

As part of the memdescs effort, struct folio will be allocated
separately from struct page and will no longer overlay the head page.

Convert the remaining &folio->page uses in mm/memory-failure.c,
mm/hwpoison-inject.c, mm/filemap.c, mm/gup_test.c, mm/memory_hotplug.c,
and mm/memremap.c to folio_page(folio, 0) (and folio_set_hwpoison() in
mf_generic_kill_procs()), and use ERR_CAST(folio) when returning an
error pointer as struct page * in do_read_cache_page() and
shmem_read_mapping_page_gfp().

In free_zone_device_folio() (mm/memremap.c), passing folio_page(folio, 0)
to wake_up_var() ensures the wake-up key continues to match the struct
page address that fs/dax.c waits on via ___wait_var_event(page, ...)
once struct folio is separated from struct page.

No functional change intended while struct folio overlays struct page.

Assisted-by: LLM
Signed-off-by: Nilay Vaish <nilayvaish@google.com>
---
 mm/filemap.c         | 6 +++---
 mm/gup_test.c        | 6 ++++--
 mm/hwpoison-inject.c | 2 +-
 mm/memory-failure.c  | 8 ++++----
 mm/memory_hotplug.c  | 2 +-
 mm/memremap.c        | 2 +-
 mm/shmem.c           | 2 +-
 7 files changed, 15 insertions(+), 13 deletions(-)

diff --git a/mm/filemap.c b/mm/filemap.c
index b74bc1e5015c..02e0c2af594c 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -156,7 +156,7 @@ static void filemap_unaccount_folio(struct address_space *mapping,
 	if (!IS_ENABLED(CONFIG_DEBUG_VM) && unlikely(folio_mapped(folio))) {
 		pr_alert("BUG: Bad page cache in process %s  pfn:%05lx\n",
 			 current->comm, folio_pfn(folio));
-		dump_page(&folio->page, "still mapped when deleted");
+		dump_page(folio_page(folio, 0), "still mapped when deleted");
 		dump_stack();
 		add_taint(TAINT_BAD_PAGE, LOCKDEP_NOW_UNRELIABLE);
 
@@ -3888,7 +3888,7 @@ static vm_fault_t filemap_map_order0_folio(struct vm_fault *vmf,
 		unsigned long *rss)
 {
 	vm_fault_t ret = 0;
-	struct page *page = &folio->page;
+	struct page *page = folio_page(folio, 0);
 
 	if (PageHWPoison(page))
 		goto out;
@@ -4239,7 +4239,7 @@ static struct page *do_read_cache_page(struct address_space *mapping,
 
 	folio = do_read_cache_folio(mapping, index, filler, file, gfp);
 	if (IS_ERR(folio))
-		return &folio->page;
+		return ERR_CAST(folio);
 	return folio_file_page(folio, index);
 }
 
diff --git a/mm/gup_test.c b/mm/gup_test.c
index ba74bf3f4104..337b58221c79 100644
--- a/mm/gup_test.c
+++ b/mm/gup_test.c
@@ -59,13 +59,15 @@ static void verify_dma_pinned(unsigned int cmd, struct page **pages,
 			if (WARN(!folio_maybe_dma_pinned(folio),
 				 "pages[%lu] is NOT dma-pinned\n", i)) {
 
-				dump_page(&folio->page, "gup_test failure");
+				dump_page(folio_page(folio, 0),
+					  "gup_test failure");
 				break;
 			} else if (cmd == PIN_LONGTERM_BENCHMARK &&
 				WARN(!folio_is_longterm_pinnable(folio),
 				     "pages[%lu] is NOT pinnable but pinned\n",
 				     i)) {
-				dump_page(&folio->page, "gup_test failure");
+				dump_page(folio_page(folio, 0),
+					  "gup_test failure");
 				break;
 			}
 		}
diff --git a/mm/hwpoison-inject.c b/mm/hwpoison-inject.c
index a11222572f97..127e5d75aa0d 100644
--- a/mm/hwpoison-inject.c
+++ b/mm/hwpoison-inject.c
@@ -131,7 +131,7 @@ static int hwpoison_inject(void *data, u64 val)
 	 * the targeted owner (or on a free page).
 	 * memory_failure() will redo the check reliably inside page lock.
 	 */
-	err = hwpoison_filter(&folio->page);
+	err = hwpoison_filter(folio_page(folio, 0));
 	if (err)
 		return 0;
 
diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index 0c96eb511997..771a75eb5505 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -1400,7 +1400,7 @@ static int __get_hwpoison_page(struct page *page, unsigned long flags)
 	 * unsupported type of folio in order to reduce the risk of unexpected
 	 * races caused by taking a folio refcount.
 	 */
-	if (!HWPoisonHandlable(&folio->page, flags))
+	if (!HWPoisonHandlable(folio_page(folio, 0), flags))
 		return -EBUSY;
 
 	if (folio_try_get(folio)) {
@@ -1777,7 +1777,7 @@ static int mf_generic_kill_procs(unsigned long long pfn, int flags,
 	if (!cookie)
 		return -EBUSY;
 
-	if (hwpoison_filter(&folio->page)) {
+	if (hwpoison_filter(folio_page(folio, 0))) {
 		rc = -EOPNOTSUPP;
 		goto unlock;
 	}
@@ -1799,7 +1799,7 @@ static int mf_generic_kill_procs(unsigned long long pfn, int flags,
 	 * Use this flag as an indication that the dax page has been
 	 * remapped UC to prevent speculative consumption of poison.
 	 */
-	SetPageHWPoison(&folio->page);
+	folio_set_hwpoison(folio);
 
 	/*
 	 * Unlike System-RAM there is no possibility to swap in a
@@ -1808,7 +1808,7 @@ static int mf_generic_kill_procs(unsigned long long pfn, int flags,
 	 * SIGBUS (i.e. MF_MUST_KILL)
 	 */
 	flags |= MF_ACTION_REQUIRED | MF_MUST_KILL;
-	collect_procs(folio, &folio->page, &to_kill, true);
+	collect_procs(folio, folio_page(folio, 0), &to_kill, true);
 
 	unmap_and_kill(&to_kill, pfn, folio->mapping, folio->index, flags);
 unlock:
diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 796af1028ee2..47bf3b5d3ff2 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -1952,7 +1952,7 @@ static void do_migrate_range(unsigned long start_pfn, unsigned long end_pfn)
 				if (__ratelimit(&migrate_rs)) {
 					pr_warn("migrating pfn %lx failed ret:%d\n",
 						folio_pfn(folio), ret);
-					dump_page(&folio->page,
+					dump_page(folio_page(folio, 0),
 						  "migration failure");
 				}
 			}
diff --git a/mm/memremap.c b/mm/memremap.c
index accba23aef28..70cfd3f05a25 100644
--- a/mm/memremap.c
+++ b/mm/memremap.c
@@ -467,7 +467,7 @@ void free_zone_device_folio(struct folio *folio)
 		break;
 
 	case MEMORY_DEVICE_FS_DAX:
-		wake_up_var(&folio->page);
+		wake_up_var(folio_page(folio, 0));
 		break;
 
 	case MEMORY_DEVICE_PCI_P2PDMA:
diff --git a/mm/shmem.c b/mm/shmem.c
index 07b2855dfb7b..1dca70978ac9 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -6195,7 +6195,7 @@ struct page *shmem_read_mapping_page_gfp(struct address_space *mapping,
 	struct page *page;
 
 	if (IS_ERR(folio))
-		return &folio->page;
+		return ERR_CAST(folio);
 
 	page = folio_file_page(folio, index);
 	if (PageHWPoison(page)) {
-- 
2.56.0.rc1.315.gc6ed9934b7-goog