[PATCH v6 2/5] nfs: track number of pinned pages in nfs_page

[Pranjal Shrivastava <praan@google.com>]

Track the number of pinned pages in nfs_page to handle unpinning
correctly, ensuring that only primary requests perform the final
unpinning operation, preventing subrequests from incorrectly
performing unpinning on behalf of their parent requests.

Add wb_nr_pinned to struct nfs_page to store the count of pinned pages
owned by the request. Update request creation and cleanup helpers to
initialize and use wb_nr_pinned for primary requests. Use the
nfs_page_array_len() helper to calculate the number of pages spanned
by a request's offset and length.

Signed-off-by: Pranjal Shrivastava <praan@google.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
---
 fs/nfs/pagelist.c        | 13 +++++++++----
 include/linux/nfs_page.h |  1 +
 2 files changed, 10 insertions(+), 4 deletions(-)

diff --git a/fs/nfs/pagelist.c b/fs/nfs/pagelist.c
index a562cfe2a126..b9ccf2a87e3c 100644
--- a/fs/nfs/pagelist.c
+++ b/fs/nfs/pagelist.c
@@ -457,6 +457,8 @@ struct nfs_page *nfs_page_create_from_page(struct nfs_open_context *ctx,
 			      offset_in_page(offset), count);
 	if (!IS_ERR(ret)) {
 		nfs_page_assign_page(ret, page, pinned);
+		if (pinned)
+			ret->wb_nr_pinned = 1;
 		nfs_page_group_init(ret, NULL);
 	}
 	nfs_put_lock_context(l_ctx);
@@ -489,6 +491,9 @@ struct nfs_page *nfs_page_create_from_folio(struct nfs_open_context *ctx,
 	ret = nfs_page_create(l_ctx, offset, folio->index, offset, count);
 	if (!IS_ERR(ret)) {
 		nfs_page_assign_folio(ret, folio, pinned);
+		if (pinned)
+			ret->wb_nr_pinned = nfs_page_array_len(offset_in_page(offset),
+							      count);
 		nfs_page_group_init(ret, NULL);
 	}
 	nfs_put_lock_context(l_ctx);
@@ -567,8 +572,8 @@ static void nfs_clear_request(struct nfs_page *req)
 
 	if (folio != NULL) {
 		if (test_and_clear_bit(PG_PINNED, &req->wb_flags)) {
-			if (req == req->wb_head)
-				unpin_user_folio(folio, 1);
+			if (req->wb_nr_pinned > 0)
+				unpin_user_folio(folio, req->wb_nr_pinned);
 		} else {
 			folio_put(folio);
 		}
@@ -576,8 +581,8 @@ static void nfs_clear_request(struct nfs_page *req)
 		clear_bit(PG_FOLIO, &req->wb_flags);
 	} else if (page != NULL) {
 		if (test_and_clear_bit(PG_PINNED, &req->wb_flags)) {
-			if (req == req->wb_head)
-				unpin_user_page(page);
+			if (req->wb_nr_pinned > 0)
+				unpin_user_pages(&page, req->wb_nr_pinned);
 		} else {
 			put_page(page);
 		}
diff --git a/include/linux/nfs_page.h b/include/linux/nfs_page.h
index fd7aafe7cb54..080fa3e23580 100644
--- a/include/linux/nfs_page.h
+++ b/include/linux/nfs_page.h
@@ -59,6 +59,7 @@ struct nfs_page {
 	struct nfs_page		*wb_this_page;  /* list of reqs for this page */
 	struct nfs_page		*wb_head;       /* head pointer for req list */
 	unsigned short		wb_nio;		/* Number of I/O attempts */
+	unsigned int		wb_nr_pinned;	/* Number of pinned pages */
 };
 
 struct nfs_pgio_mirror;
-- 
2.55.0.691.gc56d675ccc-goog