[PATCH] afs: Fix mmap

[David Howells]

Hi Linus,

Could you apply this patch please?  Note the odd email address in the
Reported-by and Tested-by fields.  That's an attempt to note Auristor's
internal testcase ID for their tracking purposes.  Is this a reasonable way
to do it?  It's kind of modelled on what syzbot does.  Would it be
preferable to use some other field or a comment after the Reported-by
instead?

David
---
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: kafs-testing+fedora34_64checkkafs-build-300 at auristor.com
Suggested-by: Marc Dionne <marc.dionne at auristor.com>
Signed-off-by: David Howells <dhowells at redhat.com>
Tested-by: kafs-testing+fedora34_64checkkafs-build-300 at auristor.com
cc: linux-afs at lists.infradead.org
Link: https://lore.kernel.org/r/686465.1639435380@warthog.procyon.org.uk/ # v1
---
 fs/afs/file.c  |    5 +++--
 fs/afs/super.c |    1 +
 2 files changed, 4 insertions(+), 2 deletions(-)


diff --git a/fs/afs/file.c b/fs/afs/file.c
index cb6ad61eec3b..afe4b803f84b 100644
--- a/fs/afs/file.c
+++ b/fs/afs/file.c
@@ -514,8 +514,9 @@ 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);
 	}
diff --git a/fs/afs/super.c b/fs/afs/super.c
index d110def8aa8e..34c68724c98b 100644
--- a/fs/afs/super.c
+++ b/fs/afs/super.c
@@ -667,6 +667,7 @@ static void afs_i_init_once(void *_vnode)
 	INIT_LIST_HEAD(&vnode->pending_locks);
 	INIT_LIST_HEAD(&vnode->granted_locks);
 	INIT_DELAYED_WORK(&vnode->lock_work, afs_lock_work);
+	INIT_LIST_HEAD(&vnode->cb_mmap_link);
 	seqlock_init(&vnode->cb_lock);
 }