[PATCH v2] netfs: Fix missing xas_retry() calls in xarray iteration

[Anthony Brennan <a2brenna@hatguy.io>]

To be applied to linux-5.15.y.

commit 59d0d52c30d4991ac4b329f049cc37118e00f5b0 upstream

Stops kernel from crashing when encountering an XAS retry entry. Patch
modified from upstream to work with pages instead of folios. Also omits
fixes to "dodgy maths" as unrelated to fixing the crash.

Signed-off-by: Anthony Brennan <a2brenna@hatguy.io>
---
 fs/netfs/read_helper.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/fs/netfs/read_helper.c b/fs/netfs/read_helper.c
index 242f8bcb34a4..4de15555bceb 100644
--- a/fs/netfs/read_helper.c
+++ b/fs/netfs/read_helper.c
@@ -248,6 +248,9 @@ static void netfs_rreq_unmark_after_write(struct netfs_read_request *rreq,
 		XA_STATE(xas, &rreq->mapping->i_pages, subreq->start / PAGE_SIZE);
 
 		xas_for_each(&xas, page, (subreq->start + subreq->len - 1) / PAGE_SIZE) {
+			if(xas_retry(&xas, page))
+				continue;
+
 			/* We might have multiple writes from the same huge
 			 * page, but we mustn't unlock a page more than once.
 			 */
@@ -403,6 +406,9 @@ static void netfs_rreq_unlock(struct netfs_read_request *rreq)
 		unsigned int pgend = pgpos + thp_size(page);
 		bool pg_failed = false;
 
+		if(xas_retry(&xas, page))
+			continue;
+
 		for (;;) {
 			if (!subreq) {
 				pg_failed = true;
-- 
2.30.2