linux-kernel - [PATCH v4 13/28] netfs: Hold a ref on a page when PG_private

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Message-ID: <161539544426.286939.4484560053278261236.stgit@warthog.procyon.org.uk>
Date:   Wed, 10 Mar 2021 16:57:24 +0000
From:   David Howells <dhowells@...hat.com>
To:     Trond Myklebust <trondmy@...merspace.com>,
        Anna Schumaker <anna.schumaker@...app.com>,
        Steve French <sfrench@...ba.org>,
        Dominique Martinet <asmadeus@...ewreck.org>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Matthew Wilcox <willy@...radead.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-mm@...ck.org, linux-cachefs@...hat.com,
        linux-afs@...ts.infradead.org, linux-nfs@...r.kernel.org,
        linux-cifs@...r.kernel.org, ceph-devel@...r.kernel.org,
        v9fs-developer@...ts.sourceforge.net,
        linux-fsdevel@...r.kernel.org, dhowells@...hat.com,
        Jeff Layton <jlayton@...hat.com>,
        David Wysochanski <dwysocha@...hat.com>,
        "Matthew Wilcox (Oracle)" <willy@...radead.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        linux-cachefs@...hat.com, linux-afs@...ts.infradead.org,
        linux-nfs@...r.kernel.org, linux-cifs@...r.kernel.org,
        ceph-devel@...r.kernel.org, v9fs-developer@...ts.sourceforge.net,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH v4 13/28] netfs: Hold a ref on a page when PG_private_2 is set

Take a reference on a page when PG_private_2 is set and drop it once the
bit is unlocked[1].

Reported-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: David Howells <dhowells@...hat.com>
cc: Matthew Wilcox <willy@...radead.org>
cc: Linus Torvalds <torvalds@...ux-foundation.org>
cc: linux-mm@...ck.org
cc: linux-cachefs@...hat.com
cc: linux-afs@...ts.infradead.org
cc: linux-nfs@...r.kernel.org
cc: linux-cifs@...r.kernel.org
cc: ceph-devel@...r.kernel.org
cc: v9fs-developer@...ts.sourceforge.net
cc: linux-fsdevel@...r.kernel.org
Link: https://lore.kernel.org/r/CAHk-=wh+2gbF7XEjYc=HV9w_2uVzVf7vs60BPz0gFA=+pUm3ww@mail.gmail.com/ [1]
Link: https://lore.kernel.org/r/1331025.1612974993@warthog.procyon.org.uk/
Link: https://lore.kernel.org/r/161340400833.1303470.8070750156044982282.stgit@warthog.procyon.org.uk/ # v3
---

 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 0a7b76c11c98..ce11ca4c32e4 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>
@@ -238,10 +239,13 @@ static void netfs_rreq_unmark_after_write(struct netfs_read_request *rreq,
 					  bool was_async)
 {
 	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) {
@@ -255,6 +259,8 @@ 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;
 		}
 	}
@@ -413,8 +419,10 @@ 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;