Revert "mm: remove PG_error"

This reverts commit 09022bc196.
This is commit needs to be reinstated as PG_error is still used by
incfs.

Bug: 367265496
Change-Id: Iaaf98f9d0c3e9d919ba87862fcf249d685b91a91
Signed-off-by: Matthias Maennich <maennich@google.com>

fs/proc/page.c

@@ -182,6 +182,7 @@ u64 stable_page_flags(const struct page *page)
 #endif
 
 	u |= kpf_copy_bit(k, KPF_LOCKED,	PG_locked);
+	u |= kpf_copy_bit(k, KPF_ERROR,		PG_error);
 	u |= kpf_copy_bit(k, KPF_DIRTY,		PG_dirty);
 	u |= kpf_copy_bit(k, KPF_UPTODATE,	PG_uptodate);
 	u |= kpf_copy_bit(k, KPF_WRITEBACK,	PG_writeback);

include/linux/page-flags.h

@@ -66,6 +66,8 @@
  * PG_referenced, PG_reclaim are used for page reclaim for anonymous and
  * file-backed pagecache (see mm/vmscan.c).
  *
+ * PG_error is set to indicate that an I/O error occurred on this page.
+ *
  * PG_arch_1 is an architecture specific page state bit.  The generic code
  * guarantees that this bit is cleared for a page when it first is entered into
  * the page cache.
@@ -101,6 +103,7 @@ enum pageflags {
 	PG_waiters,		/* Page has waiters, check its waitqueue. Must be bit #7 and in the same byte as "PG_locked" */
 	PG_active,
 	PG_workingset,
+	PG_error,
 	PG_owner_priv_1,	/* Owner use. If pagecache, fs may use */
 	PG_owner_2,		/* Owner use. If pagecache, fs may use */
 	PG_arch_1,
@@ -184,7 +187,7 @@ enum pageflags {
 	 */
 
 	/* At least one page in this folio has the hwpoison flag set */
-	PG_has_hwpoisoned = PG_active,
+	PG_has_hwpoisoned = PG_error,
 	PG_large_rmappable = PG_workingset, /* anon or file-backed */
 	PG_partially_mapped = PG_reclaim, /* was identified to be partially mapped */
 };
@@ -508,6 +511,7 @@ static inline int TestClearPage##uname(struct page *page) { return 0; }
 
 __PAGEFLAG(Locked, locked, PF_NO_TAIL)
 FOLIO_FLAG(waiters, FOLIO_HEAD_PAGE)
+PAGEFLAG(Error, error, PF_NO_TAIL) TESTCLEARFLAG(Error, error, PF_NO_TAIL)
 FOLIO_FLAG(referenced, FOLIO_HEAD_PAGE)
 	FOLIO_TEST_CLEAR_FLAG(referenced, FOLIO_HEAD_PAGE)
 	__FOLIO_SET_FLAG(referenced, FOLIO_HEAD_PAGE)

include/trace/events/mmflags.h

@@ -100,6 +100,7 @@
 #define __def_pageflag_names						\
 	DEF_PAGEFLAG_NAME(locked),					\
 	DEF_PAGEFLAG_NAME(waiters),					\
+	DEF_PAGEFLAG_NAME(error),					\
 	DEF_PAGEFLAG_NAME(referenced),					\
 	DEF_PAGEFLAG_NAME(uptodate),					\
 	DEF_PAGEFLAG_NAME(dirty),					\

include/uapi/linux/kernel-page-flags.h

@@ -7,7 +7,7 @@
  */
 
 #define KPF_LOCKED		0
-#define KPF_ERROR		1	/* Now unused */
+#define KPF_ERROR		1
 #define KPF_REFERENCED		2
 #define KPF_UPTODATE		3
 #define KPF_DIRTY		4