[PATCH 13/33] netfs: Hold a ref on a page when PG_private_2 is set

[David Howells <dhowells@redhat.com>]

Take a reference on a page when PG_private_2 is set and drop it once the
bit is unlocked.

Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: David Howells <dhowells@redhat.com>
cc: Matthew Wilcox <willy@infradead.org>
cc: Linus Torvalds <torvalds@linux-foundation.org>
cc: linux-mm@kvack.org
cc: linux-cachefs@redhat.com
cc: linux-afs@lists.infradead.org
cc: linux-nfs@vger.kernel.org
cc: linux-cifs@vger.kernel.org
cc: ceph-devel@vger.kernel.org
cc: v9fs-developer@lists.sourceforge.net
cc: linux-fsdevel@vger.kernel.org
Link: https://lore.kernel.org/linux-fsdevel/1331025.1612974993@warthog.procyon.org.uk/
---

 fs/netfs/read_helper.c |   10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/fs/netfs/read_helper.c b/fs/netfs/read_helper.c
index 156941e0de61..9191a3617d91 100644
--- a/fs/netfs/read_helper.c
+++ b/fs/netfs/read_helper.c
@@ -10,6 +10,7 @@
 #include <linux/fs.h>
 #include <linux/mm.h>
 #include <linux/pagemap.h>
+#include <linux/pagevec.h>
 #include <linux/slab.h>
 #include <linux/uio.h>
 #include <linux/sched/mm.h>
@@ -230,10 +231,13 @@ static void netfs_rreq_completed(struct netfs_read_request *rreq)
 static void netfs_rreq_unmark_after_write(struct netfs_read_request *rreq)
 {
 	struct netfs_read_subrequest *subreq;
+	struct pagevec pvec;
 	struct page *page;
 	pgoff_t unlocked = 0;
 	bool have_unlocked = false;
 
+	pagevec_init(&pvec);
+
 	rcu_read_lock();
 
 	list_for_each_entry(subreq, &rreq->subrequests, rreq_link) {
@@ -247,6 +251,8 @@ static void netfs_rreq_unmark_after_write(struct netfs_read_request *rreq)
 				continue;
 			unlocked = page->index;
 			unlock_page_fscache(page);
+			if (pagevec_add(&pvec, page) == 0)
+				pagevec_release(&pvec);
 			have_unlocked = true;
 		}
 	}
@@ -403,8 +409,10 @@ static void netfs_rreq_unlock(struct netfs_read_request *rreq)
 				pg_failed = true;
 				break;
 			}
-			if (test_bit(NETFS_SREQ_WRITE_TO_CACHE, &subreq->flags))
+			if (test_bit(NETFS_SREQ_WRITE_TO_CACHE, &subreq->flags)) {
+				get_page(page);
 				SetPageFsCache(page);
+			}
 			pg_failed |= subreq_failed;
 			if (pgend < iopos + subreq->len)
 				break;