linux-kernel - [PATCH 4/6] netfs: Fix the loop that unmarks folios after writing to the cache

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Message-ID: <20240109112029.1572463-5-dhowells@redhat.com>
Date: Tue,  9 Jan 2024 11:20:21 +0000
From: David Howells <dhowells@...hat.com>
To: Christian Brauner <christian@...uner.io>,
	Jeff Layton <jlayton@...nel.org>,
	Gao Xiang <hsiangkao@...ux.alibaba.com>,
	Dominique Martinet <asmadeus@...ewreck.org>
Cc: David Howells <dhowells@...hat.com>,
	Steve French <smfrench@...il.com>,
	Matthew Wilcox <willy@...radead.org>,
	Marc Dionne <marc.dionne@...istor.com>,
	Paulo Alcantara <pc@...guebit.com>,
	Shyam Prasad N <sprasad@...rosoft.com>,
	Tom Talpey <tom@...pey.com>,
	Eric Van Hensbergen <ericvh@...nel.org>,
	Ilya Dryomov <idryomov@...il.com>,
	linux-cachefs@...hat.com,
	linux-afs@...ts.infradead.org,
	linux-cifs@...r.kernel.org,
	linux-nfs@...r.kernel.org,
	ceph-devel@...r.kernel.org,
	v9fs@...ts.linux.dev,
	linux-erofs@...ts.ozlabs.org,
	linux-fsdevel@...r.kernel.org,
	linux-mm@...ck.org,
	netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH 4/6] netfs: Fix the loop that unmarks folios after writing to the cache

In the loop in netfs_rreq_unmark_after_write() that removes the PG_fscache
from folios after they've been written to the cache, as soon as we remove
the mark from a multipage folio, it can get split - and then we might see a
fragment of folio again.

Guard against this by advancing the 'unlocked' tracker to the index of the
last page in the folio to avoid a double removal of the PG_fscache mark.

Reported-by: Marc Dionne <marc.dionne@...istor.com>
Signed-off-by: David Howells <dhowells@...hat.com>
cc: Matthew Wilcox <willy@...radead.org>
cc: linux-afs@...ts.infradead.org
cc: linux-cachefs@...hat.com
cc: linux-fsdevel@...r.kernel.org
cc: linux-mm@...ck.org
---
 fs/netfs/buffered_write.c | 1 +
 fs/netfs/io.c             | 2 +-
 2 files changed, 2 insertions(+), 1 deletion(-)

diff --git a/fs/netfs/buffered_write.c b/fs/netfs/buffered_write.c
index 6cd8f7422e9a..0b2b7a60dabc 100644
--- a/fs/netfs/buffered_write.c
+++ b/fs/netfs/buffered_write.c
@@ -698,6 +698,7 @@ static void netfs_pages_written_back(struct netfs_io_request *wreq)
 	end_wb:
 		if (folio_test_fscache(folio))
 			folio_end_fscache(folio);
+		xas_advance(&xas, folio_next_index(folio) - 1);
 		folio_end_writeback(folio);
 	}
 
diff --git a/fs/netfs/io.c b/fs/netfs/io.c
index 5b5af96cd4b9..4309edf33862 100644
--- a/fs/netfs/io.c
+++ b/fs/netfs/io.c
@@ -126,7 +126,7 @@ static void netfs_rreq_unmark_after_write(struct netfs_io_request *rreq,
 			 */
 			if (have_unlocked && folio_index(folio) <= unlocked)
 				continue;
-			unlocked = folio_index(folio);
+			unlocked = folio_next_index(folio) - 1;
 			trace_netfs_folio(folio, netfs_folio_trace_end_copy);
 			folio_end_fscache(folio);
 			have_unlocked = true;