[PATCH 16/21] xfs: improve detection of lost xfile contents

[Christoph Hellwig <hch@lst.de>]

From: "Darrick J. Wong" <djwong@kernel.org>

shmem files are weird animals with respect to figuring out if we've lost
any data.  The memory failure code can set HWPoison on a page, but it
also sets writeback errors on the file mapping.  Replace the twisty
multi-line if logic with a single helper that looks in all the places
that I know of where memory errors can show up.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 fs/xfs/scrub/xfile.c | 33 +++++++++++++++++++++++++++------
 1 file changed, 27 insertions(+), 6 deletions(-)

diff --git a/fs/xfs/scrub/xfile.c b/fs/xfs/scrub/xfile.c
index 077f9ce6e81409..2d802c20a8ddfe 100644
--- a/fs/xfs/scrub/xfile.c
+++ b/fs/xfs/scrub/xfile.c
@@ -99,6 +99,31 @@ xfile_destroy(
 	kfree(xf);
 }
 
+/* Has this file lost any of the data stored in it? */
+static inline bool
+xfile_has_lost_data(
+	struct inode		*inode,
+	struct folio		*folio)
+{
+	struct address_space	*mapping = inode->i_mapping;
+
+	/* This folio itself has been poisoned. */
+	if (folio_test_hwpoison(folio))
+		return true;
+
+	/* A base page under this large folio has been poisoned. */
+	if (folio_test_large(folio) && folio_test_has_hwpoisoned(folio))
+		return true;
+
+	/* Data loss has occurred anywhere in this shmem file. */
+	if (test_bit(AS_EIO, &mapping->flags))
+		return true;
+	if (filemap_check_wb_err(mapping, 0))
+		return true;
+
+	return false;
+}
+
 /*
  * Load an object.  Since we're treating this file as "memory", any error or
  * short IO is treated as a failure to allocate memory.
@@ -138,9 +163,7 @@ xfile_load(
 				PAGE_SIZE - offset_in_page(pos));
 			memset(buf, 0, len);
 		} else {
-			if (folio_test_hwpoison(folio) ||
-			    (folio_test_large(folio) &&
-			     folio_test_has_hwpoisoned(folio))) {
+			if (xfile_has_lost_data(inode, folio)) {
 				folio_unlock(folio);
 				folio_put(folio);
 				break;
@@ -201,9 +224,7 @@ xfile_store(
 		if (shmem_get_folio(inode, pos >> PAGE_SHIFT, &folio,
 				SGP_CACHE) < 0)
 			break;
-		if (folio_test_hwpoison(folio) ||
-		    (folio_test_large(folio) &&
-		     folio_test_has_hwpoisoned(folio))) {
+		if (xfile_has_lost_data(inode, folio)) {
 			folio_unlock(folio);
 			folio_put(folio);
 			break;
-- 
2.39.2