linux-kernel - [PATCH] afs: Fix mmap

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Message-ID: <163941464554.620822.14509008966840730864.stgit@warthog.procyon.org.uk>
Date:   Mon, 13 Dec 2021 16:57:25 +0000
From:   David Howells <dhowells@...hat.com>
To:     marc.dionne@...istor.com
Cc:     dhowells@...hat.com, linux-afs@...ts.infradead.org,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] afs: Fix mmap

Fix afs_add_open_map() to check that the vnode isn't already on the list
when it adds it.  It's possible that afs_drop_open_mmap() decremented the
cb_nr_mmap counter, but hadn't yet got into the locked section to remove
it.

Also vnode->cb_mmap_link should be initialised, so fix that too.

Fixes: 6e0e99d58a65 ("afs: Fix mmap coherency vs 3rd-party changes")
Reported-by: Marc Dionne <marc.dionne@...istor.com>
Signed-off-by: David Howells <dhowells@...hat.com>
cc: linux-afs@...ts.infradead.org
---

 fs/afs/file.c |    5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/fs/afs/file.c b/fs/afs/file.c
index 572063dad0b3..bcda99dcfdec 100644
--- a/fs/afs/file.c
+++ b/fs/afs/file.c
@@ -539,8 +539,9 @@ static void afs_add_open_mmap(struct afs_vnode *vnode)
 	if (atomic_inc_return(&vnode->cb_nr_mmap) == 1) {
 		down_write(&vnode->volume->cell->fs_open_mmaps_lock);
 
-		list_add_tail(&vnode->cb_mmap_link,
-			      &vnode->volume->cell->fs_open_mmaps);
+		if (list_empty(&vnode->cb_mmap_link))
+			list_add_tail(&vnode->cb_mmap_link,
+				      &vnode->volume->cell->fs_open_mmaps);
 
 		up_write(&vnode->volume->cell->fs_open_mmaps_lock);
 	}